US and UK tax returns, prepared together by one firm

You file a US federal return if you are a US citizen or green card holder with gross income above the filing threshold, wherever you live. You file a UK Self Assessment return if you are UK resident and have income HMRC cannot collect through PAYE, which includes almost any foreign income.

The US side: citizenship, not residence

The United States taxes on citizenship. A US citizen who has lived in London for twenty years, earns only a UK salary and has never held a US bank account still has the same filing duty as someone in Ohio. The IRS states the rule plainly in its guidance on filing requirements for US citizens and resident aliens abroad: your worldwide income is subject to US income tax regardless of where you live.

A US person, for these purposes, is any of the following:

• A US citizen, including someone born in the US who left as a baby and someone born abroad to a US parent who passed on citizenship. These are often called accidental Americans.
• A green card holder, until the card is formally given up or a treaty position is taken. An expired card does not end US tax residence on its own.
• Someone who meets the substantial presence test by spending enough days in the United States.

The duty to file starts when your gross income from all sources worldwide reaches the threshold for your filing status. Gross income means income before any exclusion, so a salary that will later be fully excluded or covered by credits still counts.

The first three rows follow the standard deduction, which the 2025 budget legislation raised and which the IRS confirmed in its inflation adjustments for tax year 2026. People aged 65 or over have slightly higher thresholds. The fourth row is the one that catches Americans in the UK. If you are married to someone who is not a US person and you do not file jointly, your status is normally married filing separately, and the threshold is five dollars. In practice every American married to a British spouse has to file.

Separate from the income tax return, you file a Report of Foreign Bank and Financial Accounts (FBAR) if your non-US accounts together held more than $10,000 at any point in the year. That has nothing to do with income. See our FBAR and FATCA guide.

The UK side: residence, then the type of income

The UK taxes on residence. Residence is decided each tax year by the Statutory Residence Test, which HMRC explains in its RDR3 guidance on the Statutory Residence Test. Spend 183 days or more in the UK in a tax year and you are resident. Below that, the answer depends on your home, your work and your ties to the UK. If you are resident, the UK taxes your worldwide income and gains.

Being UK resident does not by itself mean you file a return. Most UK employees never do, because Pay As You Earn (PAYE) collects the right tax from their salary. You must file when you have income or gains that PAYE does not deal with. HMRC's list of who must send a tax return includes anyone who:

• was self-employed as a sole trader and earned more than £1,000, or was a partner in a partnership;
• had Capital Gains Tax to pay;
• has to pay the High Income Child Benefit Charge and does not pay it through PAYE;
• has untaxed income such as rent, savings interest, dividends or foreign income.

The last item is why nearly every American in the UK is in Self Assessment. Interest on a US savings account, dividends in a US brokerage account, rent from a house you kept in the States, a distribution from an Individual Retirement Account: all of it is foreign income to HMRC. If you are not sure, HMRC has a tool to check if you need to send a Self Assessment tax return.

UK residents with US obligations who are not American

Some people on the UK side of this are not US citizens at all. A British citizen who holds a green card and has moved home is still a US person. A UK resident who owns US rental property, or who receives US-source income as a non-resident, files Form 1040-NR on that income. A British spouse who elects to file jointly with an American spouse becomes a US filer on worldwide income. Each of these needs both returns to agree, for the same reasons.

If you have not been filing

Many people learn about the US requirement years after it began. If you have never filed, or stopped when you moved, the IRS has a route designed for you. The Streamlined Foreign Offshore Procedures ask for three years of returns and six years of FBARs, with penalties waived where the failure was not wilful. Read our guide to IRS streamlined filing before you file anything, because sending in late returns one at a time can close that route.

The US tax year is the calendar year, 1 January to 31 December. The UK tax year runs from 6 April to the following 5 April. Each US return therefore takes about three months from one UK tax year and nine months from the next, and every figure has to be rebuilt from dated records.

This is the most practical problem in dual filing, and the one that documents do not solve for you. A UK employer gives you a P60 after 5 April showing pay and tax for the UK year. A UK bank gives you an interest certificate for the UK year. A US broker gives you a Form 1099 for the calendar year. None of them matches the other country's period.

How employment income is re-cut

For the US return you need pay received between 1 January and 31 December. That is the last three months of one UK tax year and the first nine of the next. The reliable way to get it is from payslips: take the cumulative year-to-date pay on your December payslip, then add the pay for January, February, March and the days to 5 April from the earlier year. The P60 on its own gives the wrong answer.

Take an example. Suppose Hannah, a US citizen in London, earns a salary of £120,000 paid evenly through the year, and receives a £30,000 bonus in March 2026. Her P60 for the UK year 2025-26 shows £150,000. Her US return for 2025 should show £120,000, because the bonus was paid in 2026. A preparer who types the P60 figure into the 2025 Form 1040 overstates her income by £30,000. At the IRS yearly average rate for 2025 of 0.759 pounds to the dollar, that is about $39,500 of income reported a year early. The same bonus then has to appear on the 2026 return, or be left off it by mistake.

The UK tax moves with the pay. PAYE deducted from the March 2026 bonus is tax on 2026 income for US purposes. If it is claimed as a credit on the 2025 return, the 2025 credit is too high and the 2026 credit is too low.

How investment income is re-cut

Interest and dividends are taxed in both countries when they are paid, so each payment is placed by date. A dividend paid on 20 February 2026 is 2026 income for the IRS and 2025-26 income for HMRC. A dividend paid on 20 April 2026 is 2026 income for the IRS and 2026-27 income for HMRC. You need a dated transaction list from every account, not just the annual summary.

Capital gains follow the date of disposal. A sale on 10 March 2026 is in the US year 2026 and the UK year 2025-26. The UK tax on it is due by 31 January 2027. The US tax on it is due by 15 April 2027. A sale on 10 May 2025 is in the US year 2025, with US tax due by 15 April 2026, and in the UK year 2025-26, with UK tax due by 31 January 2027. In that second case the US tax falls due nine months before the UK tax. That gap is the source of one of the most expensive errors in dual filing, covered in the section on what goes wrong.

Self-employment and rental income

If you are self-employed, UK profits are now taxed on a tax-year basis, so your UK accounts effectively run to 5 April or 31 March. The US return needs calendar-year profit. That means two sets of figures drawn from the same bookkeeping: income and expenses from January to December for Schedule C, and from April to April for the UK self-employment pages. The same applies to rental property, with one further difference. The US requires depreciation on a rental building. The UK does not allow it. The rental profit will differ between the two returns even for the same twelve months.

When UK tax counts for US credit: paid or accrued

The US gives a foreign tax credit for UK tax either in the year you paid it or in the year it accrued. You choose the method, and it applies to all your foreign taxes. IRS Publication 514 on the foreign tax credit for individuals explains both.

• Paid basis. You credit UK tax in the US year the money left your hands. PAYE deducted from January to December 2025 is credited in 2025. A balancing payment made to HMRC on 31 January 2026 is credited in 2026, even though it relates to UK income from 2024-25.
• Accrued basis. You credit UK tax in the US year in which the UK tax year ends. All UK tax for 2025-26 accrues on 5 April 2026 and is credited on the 2026 US return, including the part deducted through PAYE in 2025.

Neither is right for everyone. Employees with steady pay often do well on the paid basis. People with large one-off gains or self-employment income often need the accrued basis, because their UK tax is paid long after the income arose. Once you choose accrual you must keep using it in later years. The choice should be made deliberately, with both returns in view, and it is one of the first things we settle on a new file.

The year you arrive or leave

In the year you move to or from the UK, HMRC can split the tax year into a resident part and a non-resident part. This is called split-year treatment. It means the UK taxes your foreign income only for the part of the year after you arrive or before you leave. The US has no equivalent for citizens: your whole calendar year is taxable. So an arrival year has four periods to keep apart, and the UK tax on the resident part is all the credit you have against a full year of US tax.

The US return is in dollars and the UK return is in pounds, and each country sets its own conversion rules. Regular income is normally converted at an average rate for the year. Single large transactions are converted at the rate on the day, and FBAR balances at a fixed year-end rate.

Converting pounds to dollars for the IRS

The IRS says it has no official exchange rate and generally accepts any posted rate that you use consistently. It publishes its own table of yearly average currency exchange rates, and most preparers use it for income received evenly through the year, such as salary, pension payments, rent and regular interest. For 2025 the IRS average for the UK pound is 0.759 pounds to one dollar. For 2024 it was 0.783.

The average rate is not right for everything. The rules that matter are:

• One-off receipts such as a bonus, a property sale or a large dividend should be converted at the spot rate on the day of the transaction.
• Capital gains need two conversions. The purchase price is converted at the rate on the day you bought, and the sale proceeds at the rate on the day you sold. You cannot work out the gain in pounds and convert the answer.
• UK tax claimed as a credit is converted at the rate on the day you paid it if you use the paid basis, and generally at the average rate for the year it relates to if you use the accrued basis.
• FBAR balances must be converted at the Treasury's year-end rate, published in the Treasury Reporting Rates of Exchange. This is a different figure from the IRS average.

Why the capital gains rule matters so much

Because each side of a sale is converted on its own date, the dollar gain can be very different from the sterling gain. Suppose you bought a flat in London for £500,000 when the pound was worth $1.25, and sold it years later for the same £500,000 when the pound was worth $1.32. In sterling you made nothing. In dollars you bought for $625,000 and sold for $660,000, a gain of $35,000 that goes on the US return. If the flat was your main home, the US exclusion of up to $250,000 of gain will normally cover it. If it was a rental, it is taxable with no UK tax to credit against it, because the UK saw no gain.

The same arithmetic applies to a sterling mortgage. If the pound has fallen against the dollar between the day you borrowed and the day you repaid, you repaid fewer dollars than you borrowed, and the US treats the difference as taxable income. It is one of the least expected lines on an American's return in the year they sell or remortgage a UK home. Our property gains service deals with both calculations.

Converting dollars to pounds for HMRC

HMRC also accepts either the rate on the date the income arose or an average rate for the period, as long as you are consistent. It publishes monthly, yearly average and spot rates, now hosted on the trade tariff service as HMRC average exchange rates. For UK Capital Gains Tax the rule is the same as the US rule in mirror image: convert the dollar cost at the rate on the purchase date and the dollar proceeds at the rate on the sale date. A US share that has not moved in dollar terms can show a sterling gain.

Why the two returns never show the same number

It follows that the same income will not be the same figure on both returns, even after allowing for the exchange rate. The periods differ, the rates differ, and the method for gains differs. That is normal. What must be true is that both figures can be traced back to the same underlying transactions. If HMRC or the IRS asks how a number was reached, the answer should be a list of dated payments and the rate applied to each, not a second preparer's estimate of the first preparer's work.

On our files the transaction list is kept once, in the original currency, with the date. The dollar and sterling figures are both calculated from it. Nothing is converted twice, and nothing is copied from one return to the other by hand.

US tax for a calendar year is due on 15 April, and Americans living abroad get an automatic extension to file until 15 June, then 15 October on request. UK tax for a tax year is due on 31 January, when the online return is also due. The FBAR is due on 15 April with an automatic extension to 15 October.

The table sets out one full cycle: US tax year 2025 and UK tax year 2025-26, with the dates either side that fall in the same twelve months. Dates that land on a weekend or holiday move to the next working day for US purposes.

The US dates in detail

If you live outside the United States on 15 April, you get two extra months to file without asking. You attach a statement to the return saying you qualify. The IRS describes this in Publication 54, the tax guide for US citizens and resident aliens abroad. The extension is for filing only. Interest runs from 15 April on anything you owe, so the payment date does not move.

If you need longer, you file Form 4868, the application for an automatic extension of time to file, by 15 June. That takes you to 15 October. Filers abroad can then ask, by letter, for a further two months to 15 December. That last extension is at the discretion of the IRS.

The FBAR has its own track. It is due on 15 April and extended automatically to 15 October, with no form to file. It goes to the Financial Crimes Enforcement Network, not the IRS, through the FinCEN page for reporting foreign bank and financial accounts.

If you expect to owe US tax of $1,000 or more after credits, the US expects it in quarterly instalments using Form 1040-ES for estimated tax. Most Americans on UK salaries owe nothing after credits and never pay estimates. Those with US investment income, US rental property or income the UK taxes lightly often should.

The UK dates in detail

HMRC's Self Assessment deadlines are fixed. For 2025-26 you register by 5 October 2026 if you are new, file on paper by 31 October 2026 or online by 31 January 2027, and pay by 31 January 2027. There is no extension to request.

Payments on account are advance payments towards the next year's bill. HMRC explains them in its guidance on payments on account. Each is half of the previous year's Self Assessment bill, due on 31 January and 31 July. You do not make them if last year's bill was under £1,000 or if more than 80% of your tax was collected at source. The first year they apply, the January payment is one and a half times what you expected: the whole of last year's balance plus half again towards this year.

Why the order of filing matters

Look at the gap. The UK return for 2025-26 can be filed any time from 6 April 2026. The US return for 2025 is due, with extensions, by 15 October 2026. If the US return needs the UK tax figure for 2025-26, which it does on the accrued basis and often on the paid basis too, the UK return has to be at least calculated before the US return is finished. A UK accountant who starts work in January 2027 is nine months too late to help.

We prepare the UK return first, in the spring and summer, and finish the US return from it. Both are normally ready well before 15 October. You then pay HMRC in January knowing exactly what the US has already credited.

Almost every American in the UK files Form 1040 with either Form 1116 or Form 2555, Schedule B and an FBAR, and on the UK side the SA100 return with the foreign and residence pages. Beyond those, each form is triggered by something specific you own or did.

US forms and what triggers them

Two points on this table. First, the Form 8938 and FBAR thresholds measure different things and neither replaces the other. The IRS sets them out in its comparison of Form 8938 and FBAR requirements. Second, the forms with the heaviest penalties are the ones triggered by ordinary British financial life: a stocks and shares ISA holding funds, a workplace pension, a small limited company. The IRS page about Form 8621 gives a sense of how much a single fund holding can require. Our PFIC reporting service and FBAR and FATCA service cover those filings.

UK forms and what triggers them

The foreign pages are where the US and UK returns meet. HMRC publishes the form and its notes on the SA106 foreign pages. Every item of US income goes there with the US tax paid on it, and the relief claimed is the figure that has to match the US return. The SA109 residence pages cannot be filed through HMRC's own free online service. They need commercial software or a paper return, which is one reason people in their arrival year often miss the claim.

Forms you give to other people

Two more forms are never filed with a tax authority but shape both returns. A Form W-9 tells a US bank or broker you are a US person, so it withholds nothing and reports your income on a Form 1099. A Form W-8BEN tells it you are a foreign person entitled to treaty rates. A US citizen must use the W-9, wherever they live. If a British spouse holds US investments, the W-8BEN brings US withholding on dividends down to the treaty rate of 15%.

Each country gives a credit for tax the other has properly charged on the same income, and the US-UK treaty sets the order. The country where the income comes from taxes first, the country of residence credits that tax, and for US citizens in the UK a third step lets the US credit the UK tax that remains.

The two credits, defined

The US foreign tax credit is a dollar-for-dollar reduction in US income tax for income tax paid to another country on foreign-source income. It is claimed on Form 1116. It is limited to the US tax on your foreign-source income, calculated separately for each category, mainly general income such as salary and passive income such as interest and dividends. The IRS overview of the foreign tax credit covers the basic rules. Unused credit can be carried back one year and forward ten.

UK Foreign Tax Credit Relief is a reduction in UK tax for foreign tax paid on income or gains the UK also taxes. It is claimed on the foreign pages of the Self Assessment return. HMRC's guidance on relief when foreign income is taxed twice gives the two limits: you cannot get more relief than the UK tax on that income, and you cannot get more than the double taxation agreement allows the other country to charge. Unused UK relief is lost. It cannot be carried anywhere.

The simple case: UK salary

For a US citizen working in the UK for a UK employer, the salary is UK-source. The UK taxes it first through PAYE. The US taxes it too, and gives a foreign tax credit for the UK tax. UK income tax rates reach 40% above £50,270 and 45% above £125,140 for 2026-27, as set out in HMRC's Income Tax rates and Personal Allowances. US federal rates at the same income are lower. The credit usually wipes out the US tax on the salary and leaves a surplus to carry forward.

The alternative is the Foreign Earned Income Exclusion, claimed on Form 2555, which removes up to $130,000 of foreign earnings from the 2025 return. For most people in the UK the credit is the better route, because UK tax is higher than US tax and the exclusion gives up things the credit keeps. We explain the trade-off in the next section.

The harder case: US-source income

Now take US dividends, US bank interest, or rent from a house in the United States. The income comes from the US and you live in the UK. Under the treaty the UK, as your country of residence, taxes the income and gives credit for US tax. But the US is also taxing you as a citizen at full rates, which is more than the treaty lets it charge a UK resident who is not American. The treaty deals with this in Article 24, and the calculation has three steps.

1. The UK gives credit only for the US tax the treaty would allow on a non-citizen. For dividends that is 15%. For most bank interest it is nil. For rent from US land it is the full US tax, because the treaty lets the country where the property is tax it without limit.
2. The UK charges its own tax on the income, less that credit.
3. The US then gives a foreign tax credit for the UK tax from step two. To make this work, the treaty treats enough of the income as UK-source for the credit to be usable. This is the re-sourcing rule, and it is claimed on a separate Form 1116 for income re-sourced by treaty, with a Form 8833 disclosure.

The text is in the UK-USA double taxation convention published by HMRC, and the IRS keeps the same treaty and its technical explanation among its United Kingdom tax treaty documents.

A worked example with US dividends

Suppose Priya is a US citizen living in Manchester and a higher-rate UK taxpayer. In 2025 she receives $10,000 of dividends from US companies through a US brokerage account. Her broker holds a Form W-9, so nothing is withheld. To keep the arithmetic visible, the figures are all in dollars and ignore the UK dividend allowance.

• US tax as a citizen. Her qualified dividends are taxed at 20%: $2,000.
• Step one. The UK allows credit for US tax at the treaty rate of 15%: $1,500.
• Step two. UK tax at the higher dividend rate of 33.75% for 2025-26 is $3,375. Less the $1,500 credit, she pays HMRC $1,875.
• Step three. The US credits UK tax against the part of its own tax above 15%. That is $500. Her US tax falls from $2,000 to $1,500.

Priya pays $1,500 to the IRS and $1,875 to HMRC, $3,375 in all. That equals the higher of the two countries' rates, which is the result the treaty is designed to give. From 6 April 2026 the UK higher dividend rate is 35.75%, shown in HMRC's guidance on tax on dividends, so the UK share rises and the total follows it.

Why the order cannot be changed

Step three needs the answer to step two, and step two needs the answer to step one. The US return cannot be finished until the UK tax on that income is known, and the UK relief cannot be claimed until someone has worked out what the US would charge a non-citizen. When one preparer does the US return in March and another does the UK return the following January, neither has the other's number. Each either guesses or leaves the credit out.

The same ordering applies, with different rates, to US interest, US pensions, US rental income and gains on US property. The US-UK double taxation treaty guide goes through each type of income, the saving clause that lets the US tax its citizens as if the treaty did not exist, and the exceptions to it. Our treaty relief service prepares the claims.

Returns prepared separately fail in a small number of repeatable ways: income cut to the wrong year, credits claimed in the wrong year or not at all, the exclusion used where the credit was better, and elections on one return that undo relief on the other. Each is avoidable when one preparer sees both returns.

1. The gain taxed twice because of timing

Suppose Daniel, a US citizen in Edinburgh, sells UK shares in May 2025 for a gain of £100,000, which is $130,000 once each side is converted on its own date. The sale is in US year 2025 and UK year 2025-26.

• UK Capital Gains Tax at 24% on the gain above the £3,000 annual exempt amount is £23,280. It is due on 31 January 2027. HMRC lists the current Capital Gains Tax rates and allowances.
• US tax at the 20% long-term rate is $26,000. It is due on 15 April 2026.

Daniel's US preparer uses the paid basis, as most do by default. On that basis the UK tax is paid in January 2027, so the credit arises in US year 2027. A foreign tax credit can be carried back one year only. It reaches 2026. It does not reach 2025. Daniel pays $26,000 to the IRS and £23,280 to HMRC on the same gain, with a credit he may never be able to use.

There are two ways to prevent this, and both need planning before the US return is filed. One is to claim credits on the accrued basis. The UK tax for 2025-26 then accrues on 5 April 2026, falls in US year 2026, and carries back one year to 2025. The other is to pay the UK tax to HMRC early, before 31 December 2025, so that it is paid in the same US year as the gain. A US-only preparer does not know the UK due date. A UK-only accountant has no reason to suggest paying thirteen months early.

Daniel may also owe the 3.8% Net Investment Income Tax, about $4,940 here. The IRS position is that foreign tax credits cannot be set against it. Whether the treaty overrides that has been argued in the US courts and is not settled. It should be raised with you, not decided silently.

2. The exclusion used by default

Software aimed at expats tends to lead with the Foreign Earned Income Exclusion, because it is simple and produces a zero. For a UK taxpayer it often costs money.

Suppose Megan is a US citizen in Leeds earning £70,000, with two children who are US citizens and have Social Security numbers. Her UK income tax is well above the US tax on the same pay. If her preparer excludes the salary on Form 2555, her US tax is nil, and that is the end of it. If the preparer claims the foreign tax credit instead, her US tax is also nil, but she can now claim the refundable part of the child tax credit. For 2025 that is up to $1,700 per child, so up to $3,400 paid to her by the IRS. The exclusion and the refundable credit cannot be claimed together.

The exclusion has other costs. UK tax on excluded income cannot be credited, so it builds no carryforward. Excluded income does not count as compensation for contributing to an Individual Retirement Account. And if you revoke the exclusion, you need IRS approval to claim it again within five tax years, as the IRS explains in its note on revoking your choice to exclude foreign earned income. Moving from the exclusion to the credit is usually right for a UK resident. It should be done once, on purpose.

3. The UK relief nobody claimed

Go back to Priya and her $10,000 of US dividends. Her UK accountant looks at the Form 1099, sees no US tax withheld, and enters the dividends on the foreign pages with no Foreign Tax Credit Relief. HMRC charges the full $3,375. Her US preparer, meanwhile, charges $2,000 and sees no UK tax on US-source income to credit. She pays $5,375 on $10,000 of dividends, when the right answer was $3,375. The $2,000 difference recurs every year until someone reads both returns together.

4. The UK election that removed the US credit

Since 6 April 2025, new arrivals in the UK can claim relief from UK tax on foreign income and gains for their first four years. For most nationalities that is a clear saving. For an American it often is not, because the US taxes the income anyway and now has no UK tax to credit.

Suppose Chris, a US citizen, arrives in London in April 2025 after a lifetime in the US. He earns a UK salary of £60,000 and has US bank interest worth £30,000. Assume his US rate on the interest is 22%, and ignore the small UK savings allowance.

• Without the claim. The UK taxes the interest at 40%: £12,000. The US tax of £6,600 is fully covered by the credit for UK tax. Total: £12,000.
• With the claim. The UK charges nothing on the interest. But claiming costs Chris his £12,570 personal allowance, which adds £5,028 of UK tax to his salary. The US charges its £6,600 in full. Total: £11,628.

The claim that looked like a £12,000 saving is worth £372, before the cost of the extra work on both returns. With a higher US rate, or state tax on top, it can leave him worse off. With much larger foreign income it can win comfortably. The point is that it has to be modelled on both returns at once. A UK accountant who makes the claim as a matter of routine has decided the US return without seeing it.

5. Mismatches the authorities can see

The IRS and HMRC exchange information. UK banks report accounts held by US persons under FATCA, and the US reports back. A US return showing £95,000 of salary against a UK return showing £120,000 for an overlapping period is not wrong in itself, because the years differ. But if the difference cannot be explained from payslips, it invites questions. So does UK tax claimed as a credit in the US that is larger than the UK tax HMRC has on record.

6. Paying twice for the same work

Two firms each collect your documents, each build a picture of your year, and each bill for it. When one finds a problem, it sends you to the other with a question you cannot answer. You pay for the overlap and for the gaps. One firm working from one file collects the documents once and answers its own questions.

Self Assessment for US citizens works the same way as for anyone else, with three additions: your US income goes on the foreign pages, your residence position may need the residence pages, and the relief you claim for US tax has to follow the treaty. You register once, receive a Unique Taxpayer Reference, and file each year by 31 January.

Who must register, and when

You must tell HMRC by 5 October after the end of the tax year in which you first had income or gains that need a return. For income first arising in 2025-26, that date was 5 October 2026. You do it through the HMRC service to register for Self Assessment, and HMRC posts you a ten-digit Unique Taxpayer Reference. If you have missed the date, register anyway. The penalty for late notification is based on tax unpaid at 31 January, so registering late and paying on time usually costs nothing.

Americans commonly have to register because of:

• interest or dividends from US accounts, however small, if tax is due on them;
• rent from a property in the United States;
• sales of US shares or funds, or of a US home;
• US pension or Social Security income;
• stock options or restricted stock units from a US parent company that PAYE has not fully taxed;
• the High Income Child Benefit Charge;
• a claim that can only be made on a return, such as split-year treatment or the foreign income and gains regime.

Your residence position comes first

Every UK return starts with a question the form barely asks: were you UK resident for the whole year, part of it, or none? The answer comes from the Statutory Residence Test in Schedule 45 to the Finance Act 2013. In the year you arrive, you will often qualify for split-year treatment, which HMRC summarises in its guidance on UK residence and tax on foreign income. The year is divided at the point you start to live or work in the UK, and foreign income from before that point stays outside UK tax. It is claimed on the residence pages. Nothing happens automatically.

The regime for foreign income and gains since April 2025

Until 5 April 2025 the UK had the remittance basis, which let people who were not domiciled in the UK keep foreign income outside UK tax as long as they did not bring it into the country. That system has gone. Domicile no longer decides how foreign income is taxed.

In its place is the foreign income and gains regime, usually called the FIG regime. It is a relief from UK tax on foreign income and gains for a person's first four tax years of UK residence, available only if they were not UK resident in any of the ten tax years before. HMRC's guidance on the 4-year foreign income and gains regime sets out the conditions. The points that matter for Americans are:

• It is claimed year by year on the Self Assessment return, and you can choose which foreign income and gains to include.
• Unlike the old system, you can bring the money to the UK without triggering tax.
• In any year you claim, you lose the income tax personal allowance and the Capital Gains Tax annual exempt amount.
• It covers foreign investment income, foreign rental and trading profits and foreign gains. It does not cover employment income, though a separate relief can apply to days worked outside the UK.
• If you arrived before 6 April 2025, you can use it only for whatever is left of your first four years.

The US taxes its citizens on that foreign income regardless. If the UK charges nothing, there is no UK tax to credit, and the US collects its tax in full. The relief is therefore worth only the amount by which UK tax would have exceeded US tax, less the cost of the lost allowances. The worked example of Chris in the previous section shows a case where that is very little. If you used the remittance basis before 2025 and still hold untaxed foreign income abroad, different transitional rules apply, and you should take advice before moving it.

Filling in the foreign pages

Each item of US income is entered in sterling with the US tax paid on it. The foreign pages ask you to list interest, dividends, pensions and property income by country, and to state the foreign tax and the relief claimed. For an American the foreign tax figure is rarely the amount on a Form 1099, because US tax on a citizen is paid through the Form 1040, not by withholding. The figure has to be worked out from the US return, capped at the treaty rate, and matched to the right UK year. This is the step that cannot be done by a preparer who has no access to the US return.

Employment income and US employers

If you work in the UK for a UK employer, PAYE handles the tax and your P60 and P11D supply the figures. Complications arise when a US parent company grants shares or options. The UK taxes them through payroll when they vest or are exercised, with the charge time-apportioned if you worked in more than one country during the vesting period. The US taxes them on its own timetable. The two countries' figures for the same grant will differ, and the credits need matching grant by grant. Our guide for founders and executives covers equity, carried interest and company ownership in detail.

High earners, lost allowances and digital reporting

Two UK features have no US counterpart. Between £100,000 and £125,140 of income, the personal allowance is withdrawn at one pound for every two, which creates an effective 60% rate in that band. And from 6 April 2026, sole traders and landlords with qualifying income above £50,000 must keep digital records and send quarterly updates under Making Tax Digital for Income Tax. The threshold falls to £30,000 in April 2027 and £20,000 in April 2028, as set out in HMRC's guidance on who must use Making Tax Digital for Income Tax. A self-employed American in the UK now has a quarterly UK reporting cycle running alongside the annual US one.

We prepare the UK return as part of the same file as the US return. See our UK Self Assessment service for what it includes.

An American married to someone who is not a US person usually files as married filing separately, or as head of household if there is a qualifying child, and can elect to file jointly by treating the spouse as a US resident. Children who are US citizens can bring a refundable US credit, and UK Child Benefit is clawed back above £60,000 of income.

Three filing statuses for a mixed-nationality couple

The UK taxes each person separately. There is no joint return and almost nothing turns on being married. The US is different: your filing status sets your rates, your standard deduction and your thresholds for almost everything. If your spouse is British and has no US status, you have three options.

The joint election is made under section 6013(g) of the Internal Revenue Code by attaching a signed statement to a joint return. The IRS guidance on a nonresident alien spouse spells out what follows. Your spouse reports worldwide income for that year and every later year until the election ends. Either of you can revoke it, but once it has ended neither of you can ever make it again. Your spouse will also need an Individual Taxpayer Identification Number, applied for on Form W-7.

The election tends to help when the British spouse has little income and few investments. It tends to hurt when they have a salary of their own, an ISA full of funds, a pension or a business, because all of that enters US reporting. It also brings their accounts into FBAR and Form 8938. Because it is effectively permanent, we work out the return both ways before anyone signs.

If you do not make the election, your spouse's own income stays off the US return. Joint accounts do not. You report the whole balance of a joint account on your FBAR, and your share of the income on your return.

Gifts between spouses

A US citizen can give unlimited amounts to a spouse who is also a US citizen. Gifts to a spouse who is not a US citizen are free of US gift tax only up to an annual limit, which is $190,000 for 2025 and $194,000 for 2026. Above that a gift tax return is required. This matters when a couple moves a house or an investment account into the British spouse's name to simplify the US return. The plan may be sound, but it needs to be done within the limits and with the UK position checked as well.

Children and the US child tax credit

A child born in the UK to a US citizen parent is usually a US citizen from birth, if the parent meets the rules on prior time spent in the United States. Once the child has a Social Security number, they can be claimed for the child tax credit. The IRS summarises the child tax credit rules as follows for 2025: up to $2,200 per qualifying child, of which up to $1,700 is refundable as the additional child tax credit if you have earned income of at least $2,500. The full credit is available up to $200,000 of income, or $400,000 on a joint return.

Two conditions catch families abroad. First, since the 2025 legislation, the parent claiming the credit must have a Social Security number valid for work, as must the child. An ITIN is not enough. Second, the refundable part is not available in a year you claim the Foreign Earned Income Exclusion. A family using the foreign tax credit can receive it. A family whose preparer used the exclusion cannot. We see this often on returns that come to us from US-only services, and earlier years can sometimes be amended to claim it.

UK Child Benefit and the high income charge

Child Benefit is a UK payment to the person responsible for a child, set at £27.05 a week for the eldest or only child and £17.90 for each other child, according to HMRC's page on what you will get from Child Benefit. It is not taxable income in the UK. But if either partner has adjusted net income above £60,000, the higher earner pays the High Income Child Benefit Charge. HMRC's guidance on the High Income Child Benefit Charge gives the rate: 1% of the benefit for every £200 of income above £60,000, so the whole amount is repaid at £80,000.

The link to the US return is that adjusted net income includes your foreign income. US dividends and interest that push you over £60,000 create a UK charge that a payroll department will not know about. The charge can now be collected through your tax code, but only if you are not already filing a return. Most Americans are.

Accounts in a child's name

A Junior ISA or a children's savings account held for a child who is a US citizen is that child's foreign account. If the child's accounts together pass $10,000, the child has an FBAR to file, signed by a parent. If the account holds UK funds, the fund reporting rules apply to the child too. A US custodial account avoids those forms but its income is taxable in the UK. Neither is wrong. Both need to be chosen knowing how each country will tax it.

Usually not, but it depends on the state you left and whether you really left it. States tax their residents and anyone with income from sources in the state. Moving abroad ends residence in most states, but a few treat you as resident until you establish a permanent home somewhere else and cut your ties.

Residence and domicile for state purposes

State domicile is the place you treat as your permanent home and intend to return to. Most states tax anyone domiciled there, and many also tax anyone who spends more than a set number of days in the state. You keep a domicile until you acquire a new one. Leaving for a two-year secondment in London, with a house, a driving licence and a voter registration left behind, may not change it. Moving with your family, selling or letting the house long-term and settling in the UK usually does.

The states differ a great deal.

• No tax on wages. Alaska, Florida, Nevada, New Hampshire, South Dakota, Tennessee, Texas, Washington and Wyoming do not tax earned income. Leaving from one of these is simple.
• Clean break on departure. Most other states stop taxing you once you move out and file a part-year return for the year you leave.
• States that hold on. California, Virginia, South Carolina and New Mexico are known for treating people who move abroad as residents for longer, particularly where the move looks temporary or ties remain. New York looks hard at anyone who keeps a home there.

California is the most important example for people in technology and finance. Its tax authority explains its approach in guidance on California residency status. It looks at where your closest connections are, not just where you sleep. California also does not follow the federal Foreign Earned Income Exclusion and gives no credit for tax paid to a foreign country. A person still treated as a California resident while working in London can owe California tax on a salary the UK has already taxed at 40%, with no relief at all.

Income from sources in a state

Even after you have plainly left, a state can tax income that arises there. The usual cases are:

• rent from a property in the state, and the gain when you sell it;
• income from a business or partnership operating in the state;
• stock options or restricted stock units earned partly while you worked in the state, even if they vest years after you moved;
• deferred pay and bonuses for work done there.

The third item surprises people who moved from California or New York to London with unvested equity. The state taxes the share of the grant that relates to the time you worked there, and the UK taxes the share that relates to UK work, and the federal return has to reconcile both. State tax on this kind of income is foreign tax from HMRC's point of view and may qualify for UK relief where the UK taxes the same income.

How to leave a state properly

The practical steps are much the same everywhere. File a part-year resident return for the year you leave, showing the date. Change your driving licence, voter registration and the address on your bank and brokerage accounts. Avoid keeping a home that is available for your use. Keep records of the days you spend in the state on visits. If you cannot use a UK address for a US account, use a relative's address in a state with no income tax only with care, because an address is evidence of where you live.

State returns are part of the federal file, since they start from the same figures. We prepare the part-year and non-resident state returns alongside the Form 1040, and where a state residence question is open we set out the evidence before a return is filed. See our US federal returns service.

A self-employed American in the UK pays UK income tax and National Insurance on profits, reports the same profits on a US Schedule C, and uses the foreign tax credit against US income tax. The US-UK totalization agreement means you pay social security contributions to one country only, which for a UK resident is the UK.

The US self-employment tax problem

US self-employment tax is the self-employed person's Social Security and Medicare contribution, charged at 15.3% on net earnings up to the Social Security wage base and 2.9% above it. It is separate from income tax. That distinction matters, because neither the Foreign Earned Income Exclusion nor the foreign tax credit reduces it. The IRS confirms in its guidance on self-employment tax for businesses abroad that you must count all your self-employment income, even the part you exclude from income tax.

So a freelance designer in Bristol with profits of $80,000 could reduce US income tax to nil and still face a US self-employment tax bill of over $11,000, on top of UK National Insurance on the same profits. The totalization agreement exists to prevent that.

What the totalization agreement does

A totalization agreement is a treaty on social security, separate from the income tax treaty, that assigns each worker to one country's system. The IRS describes the purpose of totalization agreements as eliminating dual coverage and dual contributions for the same work. The United States and the United Kingdom have had one in force since the 1980s. Under it:

• a self-employed person is covered by the country where they live. A UK resident pays UK National Insurance and is exempt from US self-employment tax;
• an employee is normally covered by the country where they work;
• an employee sent by a US employer to the UK for five years or less can stay in US Social Security and be exempt from UK contributions.

The exemption is not automatic on the return. You need a certificate of coverage, which is a document from the social security authority of the country whose system covers you. A self-employed UK resident asks HMRC for one. You keep it with your records and attach a copy or a statement to the US return each year, and Schedule SE is then not completed. Without the certificate, the IRS can assess self-employment tax, and it does.

What you pay in the UK instead

Self-employed people in the UK pay Class 4 National Insurance through Self Assessment. For 2026-27 it is 6% on profits between £12,570 and £50,270 and 2% above that, as shown in HMRC's table of self-employed National Insurance rates. Class 2 contributions are treated as paid once profits reach the small profits threshold, which protects your UK State Pension record. UK National Insurance is not an income tax and cannot be claimed as a foreign tax credit in the US. Periods of contribution in each country can be combined when you later claim a pension from either, which is the other half of what the agreement does.

Sole trader or limited company

In the UK it is common to run a small business through a limited company. For a US citizen that choice has consequences a UK accountant may not mention. A UK company you own is a foreign corporation. It brings Form 5471 every year, and its profits can be taxed to you in the US as they arise under the rules for controlled foreign corporations, whether or not you take them out. An election can sometimes be made to treat the company as transparent for US purposes, with its own reporting. None of this makes a company the wrong choice. It means the decision should be made with the US return in view, and ideally before the company is formed. Our founders and executives guide covers company ownership in depth.

Records for two countries

You will need profit for the calendar year in dollars and profit for the UK tax year in pounds, from the same books. Expenses are not treated identically. The UK has a flat-rate option for some costs and its own rules on use of home and vehicles. The US has its own depreciation rules. Keep dated records of every sale and expense, and let the two computations be drawn from them.

UK tax wrappers do not carry over to the US automatically. A UK pension is generally protected by the treaty if the right position is taken, an ISA is fully taxable in the US, and UK-domiciled funds are punitively taxed under the passive foreign investment company rules. US accounts create the mirror problem on the UK return.

This section is an overview. Each topic has more detail elsewhere, and the links are below.

UK pensions

A UK workplace pension or personal pension is a foreign trust or foreign pension from the US point of view. Under US domestic law, employer contributions and growth could be taxable to you each year. The treaty changes that. It allows a US citizen resident in the UK to treat contributions to a UK scheme much as the UK does, within US limits, and defers US tax on growth until money is paid out. The treaty position usually needs to be disclosed on Form 8833. The pension still counts as a foreign financial asset for Form 8938 and, depending on its type, as an account for the FBAR.

When you draw the pension, the general treaty rule is that periodic payments are taxed only in the country where you live. The 25% lump sum that the UK lets you take tax-free is more difficult. How the treaty applies to it for a US citizen living in the UK is read differently by different practitioners, and you should have the position explained before you take one. A Self-Invested Personal Pension raises further questions about trust reporting. Our pensions service covers contributions, transfers and withdrawals for both returns.

ISAs

An Individual Savings Account is a UK account in which interest, dividends and gains are free of UK tax, with a subscription limit of £20,000 for 2026-27 according to HMRC's guide to Individual Savings Accounts. The US does not recognise it. Interest in a cash ISA is taxable on your Form 1040 each year. Because the UK has charged nothing, there is no UK tax to credit against it.

A stocks and shares ISA is worse if it holds funds, which nearly all do. That leads to the next point.

Funds: a trap on both sides

A passive foreign investment company, or PFIC, is a non-US company whose income or assets are mainly passive. Almost every fund set up outside the United States meets the definition, including UK unit trusts, OEICs, investment trusts and exchange-traded funds listed in London or Dublin. A US person who holds one files Form 8621 for each fund each year. Unless an election is made, gains and certain distributions are taxed at the highest ordinary rate with an interest charge, and capital gains treatment is lost.

The obvious answer is to hold US funds instead. But the UK has its own rule. A fund based outside the UK that does not have reporting fund status with HMRC is taxed on sale as income, at up to 45%, not as a capital gain at up to 24%. HMRC publishes the list of offshore funds with reporting status. Most US mutual funds are not on it. UK and European rules also make it hard for a UK resident to buy US-listed funds through a retail broker at all.

So an American in the UK who buys a UK fund has a US problem, and one who buys a US fund may have a UK problem. The holdings that work on both returns are narrower: individual shares and bonds, and US funds that have UK reporting status. We do not recommend investments. We do tell you how each holding you already have will be taxed and reported in both countries, so you and your investment adviser can decide what to keep. See our PFIC reporting service.

US retirement accounts on the UK return

The treaty also protects US pensions in UK hands. Growth inside a 401(k) or a traditional IRA is generally not taxed in the UK as it arises, and distributions are taxed as pension income when paid. Roth accounts, which the US does not tax on withdrawal, are generally respected by the UK under the treaty as well. These positions are claimed on the UK return, not assumed. An ordinary US brokerage account has no such protection: its income and gains are taxable in the UK year by year, with the conversion rules described in the section on exchange rates.

Property

Your main home is largely sheltered in both countries, by private residence relief in the UK and by the US exclusion of up to $250,000 of gain, or $500,000 on a joint return. The two tests are not the same, and the currency effect can produce a US gain where the UK sees none. Rental property is taxed in both countries each year, with depreciation on the US side only, and the sale of UK residential property must be reported to HMRC within 60 days of completion under the rules for reporting and paying Capital Gains Tax on UK property.

For the treaty articles behind all of this, see our guide to the US-UK double taxation treaty. For the account reporting, see our FBAR and FATCA guide.

Choose a preparer who does both returns in-house, from one set of working papers, and can explain how the credits on each return are tied to the other. The questions that separate firms are about method, not about how many forms they list on their website.

The four kinds of preparer you will meet

Searches for a US tax accountant in London, an American tax accountant in the UK or US expat tax services in the UK return four quite different kinds of business.

A large international firm will also do both, usually for employees whose employer is paying. For individuals paying their own fees, the choice is normally among the four above.

Questions to ask before you engage anyone

1. Do you prepare both the US and the UK return yourselves? If one is sent to a partner firm, ask who reconciles them.
2. Which return do you prepare first, and why? A firm that understands the credits will have a reasoned answer tied to the deadlines.
3. Do you claim foreign tax credits on the paid or the accrued basis? Any answer that begins with your circumstances is a good sign. A blank look is not.
4. When would you use the Foreign Earned Income Exclusion for someone in the UK? The honest answer is: sometimes, not by default.
5. How do you treat US dividends and interest on my UK return? Listen for the treaty rate and the re-sourcing step.
6. What do you do about my ISA, my pension and any funds I hold? They should mention Form 8621 and the treaty without being prompted.
7. Who signs the US return? Anyone paid to prepare a US return must have a Preparer Tax Identification Number and sign it. Ask what professional standing the signer has and whether they can represent you before the IRS.
8. Who is your UK supervisory body? Accountancy firms in the UK must be supervised for anti-money laundering purposes, by a professional body or by HMRC.
9. What happens if the IRS or HMRC writes to me? Find out whether replies are included, and who writes them.
10. How is the fee set? Ask for it in writing before work starts, with what would change it.

The IRS has general advice on choosing a tax professional, including how to check a preparer's credentials. On the UK side, professional bodies such as the ICAEW keep public directories where you can look up a member firm.

Signs that a preparer is not joining the two up

• They ask you for your P60 and nothing else about your pay.
• They ask you what UK tax you paid, with no question about which year or when.
• Your US return shows the exclusion every year and nobody has discussed the alternative.
• Your UK return has no foreign pages although you have US accounts.
• Your UK foreign pages show US income but no relief for US tax, or relief for the full amount of US tax without reference to the treaty.
• Nobody has asked what is inside your ISA or pension.
• You are the only person who has seen both returns.

What dual-qualified should mean

People often look for a dual-qualified US UK tax adviser. Qualifications matter, and you should ask about them. But the practical test is narrower. Does the same team prepare both returns, in the right order, from one record of your income, and check them against each other before filing? A firm can employ people qualified in both countries and still run two separate processes. A firm that works from one file will show you one reconciliation.

That is how US UK Tax Experts works. If you want to know how your own position would be handled, send us a short description and we will reply within one working day. You can read more about the firm and see the full list of services.

The work runs in one sequence: establish your status in each country, collect one set of documents, build a dated record of income, prepare the UK return, finish the US return from it, reconcile the two, then file and schedule the payments. You gather documents once.

The steps, in order

1. First conversation. You tell us your citizenship or visa status, when you moved, what you earn and own, and what has been filed before. We tell you which returns and forms are needed and for which years.
2. Status check. We confirm UK residence under the Statutory Residence Test, including any split year, and your US filing status. If earlier years are missing, we decide whether the streamlined procedures are the right route before preparing anything.
3. One document request. You receive a single list covering both countries. Nothing is asked for twice.
4. The income record. Every item of income, gain and tax paid is entered once, by date, in its own currency.
5. UK return. The April-to-April figures are drawn from the record. Residence claims, the foreign pages and treaty-limited relief for US tax are prepared.
6. US return. The calendar-year figures are drawn from the same record. Credits for UK tax are claimed on the chosen basis, including the re-sourced credit where it applies, with the information forms your accounts require.
7. Reconciliation. The two returns are compared line by line: income, tax paid, credits claimed in each direction. Differences are explained or corrected.
8. Review with you. You see both returns and a short summary of what is owed to whom and when, and of any choices made, such as the credit basis or a filing status election.
9. Filing. The US return and the FBAR are filed electronically where the forms allow. The UK return is filed online.
10. Payments and next year. You get the dates and amounts for HMRC, including payments on account, and for the IRS, including estimates if needed. Carryforwards are recorded for next year's file.

Documents to gather

Identity and status

• Passport details, Social Security number or ITIN, UK National Insurance number and Unique Taxpayer Reference if you have one
• Dates you moved, and days spent in the UK and the US in the year
• Last year's US and UK returns, and any earlier ones if this is your first year with us

Employment

• P60, and P45 if you changed jobs
• P11D for benefits in kind
• Payslips for December and for March or April, so pay can be cut to the calendar year
• Form W-2 if you had any US employment
• Share plan statements showing grant, vesting, exercise and sale dates

Savings and investments

• Year-end statements for every bank account in any country, with the highest balance in the year
• Interest certificates and dividend vouchers
• Forms 1099 from US banks and brokers
• A dated transaction history for each investment account, including ISAs
• Fund names and identifiers for anything held in funds

Pensions

• Annual statements for each UK pension, showing your contributions, your employer's and the year-end value
• Statements for IRAs and 401(k) plans, and Forms 1099-R or SSA-1099 for anything paid out

Property and self-employment

• Rent received and expenses by date, mortgage interest statements, and purchase details for depreciation
• Completion statements for any purchase or sale
• Business income and expense records, or accounts, for the period covering both tax years
• Your certificate of coverage if you are self-employed

Tax already paid

• Your HMRC statement of account showing payments made and their dates
• Records of any US estimated payments
• State tax returns or notices

How long it takes

UK documents for a tax year are mostly available by June or July: the P60 by 31 May and the P11D by 6 July. US forms for the previous calendar year arrive from January to March. That makes summer the natural time to prepare both returns for a US year and the UK year that overlaps it. People who send documents by the end of July are normally filed in both countries well before the 15 October US date, with the UK payment known months before it falls due.

If you come to us in the autumn, as many do, the order is the same but faster. The first step is always to check that the US extension is in place. For the fuller picture of the US side, see our article on filing US taxes from the UK.

Late or wrong returns cost penalties and interest in both countries, and the US penalties for missing information forms are fixed amounts that apply even when no tax is due. The larger cost is often tax paid twice because a credit was lost, which no penalty notice ever tells you about.

US penalties on the return itself

The IRS charges a failure to file penalty of 5% of the unpaid tax for each month or part of a month a return is late, up to 25%. If a return is more than 60 days late, the minimum penalty for returns due after 31 December 2025 is $525, or the whole of the tax due if that is less. A separate failure to pay penalty runs at 0.5% a month. Interest is added to both.

These penalties are a percentage of tax owed. Most Americans in the UK owe no US tax once credits are claimed, so a late Form 1040 on its own often carries no penalty. That fact has led many people to assume late filing is harmless. It is not, for two reasons. The credits and elections that bring the tax to nil have to be claimed on a return. And the information forms carry their own penalties.

US penalties on information forms

In 2023 the Supreme Court held in Bittner v. United States that the non-wilful FBAR penalty applies per report, not per account. That reduced the exposure for people with many accounts, but one late report can still cost five figures. There is a further effect. When a required international information form is missing, the period in which the IRS can examine the whole return may stay open indefinitely.

Relief exists. Penalties can be waived for reasonable cause, and the Streamlined Foreign Offshore Procedures waive them for people living abroad whose failure was not wilful, in return for three years of returns and six years of FBARs. The details are in our streamlined filing guide, and our streamlined filing service prepares the submission.

UK penalties

HMRC's Self Assessment penalties for a late return are:

• £100 as soon as the return is late, even if no tax is due;
• £10 a day after three months, up to £900;
• a further 5% of the tax due or £300, whichever is greater, after six months;
• another 5% or £300 after twelve months.

Late payment is penalised separately at 5% of the unpaid tax at 30 days, six months and twelve months, with interest on top. Unlike the US, the UK's first penalty does not depend on owing anything. A return that is one day late costs £100.

There are also penalties for errors. If a return understates tax, HMRC can charge a percentage of the extra tax depending on whether the error was careless or deliberate and whether you told HMRC before it found out. Where the error involves offshore income or gains, the percentages can be higher and HMRC has longer to go back. For a UK resident, US accounts are offshore. HMRC will cancel a penalty if you had what it accepts as a reasonable excuse, but relying on an adviser who was not asked the right question rarely qualifies.

The cost nobody sends you a notice for

Penalties are visible. Lost relief is not. The examples earlier on this page each involved someone who filed on time in both countries and still overpaid:

• Daniel paid about $26,000 of US tax on a gain the UK had also taxed, because the credit landed in the wrong year.
• Megan missed up to $3,400 a year in refundable child credit because her return used the exclusion.
• Priya overpaid $2,000 a year because her UK return claimed no relief for US tax on her dividends.
• Chris made a UK claim expected to save £12,000 that saved £372.

Neither the IRS nor HMRC writes to tell you that you paid too much. Some of it can be recovered by amending. The US generally allows three years from the date a return was filed to claim a refund, with a longer period for foreign tax credit claims. The UK allows four years from the end of the tax year for overpayment relief. After that the money is gone.

If you think earlier returns may have been prepared without reference to each other, we can review the last few years of both and tell you whether anything is worth reopening. Email hello@usuktaxexperts.com or use the contact page.