US UK Cross Border Tax Compliance: A Year-Round Checklist

US UK cross border tax compliance: an introduction

US UK cross border tax compliance means meeting two sets of deadlines on different calendars. The US tax year follows the calendar year, while the UK tax year runs from 6 April to 5 April. As a result, an American living in Britain has filing or payment dates in most seasons of the year. Missing one side often causes problems on the other, because each return relies on figures from the other.

This article walks through a typical year, season by season, so you can see what falls due and when. Our full guide to US and UK tax returns prepared together explains how both returns share one set of figures.

Who this US UK cross border tax compliance checklist is for

The checklist suits US citizens and green card holders who live and pay tax in the UK. It also suits dual nationals who have only recently learned about US filing. If you are behind on past years, start with catching up first. Our guide to IRS Streamlined Filing from the UK covers that route.

Why two calendars cause trouble

The GOV.UK Income Tax rates page gives the current UK tax year as 6 April 2026 to 5 April 2027. The US year runs from 1 January to 31 December. Consequently, one US return draws on parts of two UK tax years. That overlap is the main reason the two returns are easier to prepare together.

What falls due between January and April?

The first months of the year carry the UK online return and payment, a US estimated payment, and the US return and FBAR. For most Americans in Britain, this is the busiest season. It is also when the records for both returns come together.

The UK online return and payment on 31 January

Self Assessment is HMRC's system for collecting tax that is not taken through PAYE. According to the GOV.UK Self Assessment deadlines page, the online return for 2025 to 2026 is due by 31 January 2027. The tax for that year is due on the same date. Furthermore, any first payment on account for the following year usually falls due then too.

The last US estimated payment on 15 January

Estimated tax is the US system of paying tax during the year on income with no withholding. The IRS estimated tax FAQs list four dates: 15 April, 15 June, 15 September and the following 15 January. Many Americans in the UK owe little because UK tax is credited. However, income the UK does not tax, such as ISA income, can create a US balance.

The US return and the FBAR on 15 April

The US return is due on 15 April, and any tax owed is due then too. The FBAR is the yearly report of foreign financial accounts, filed with FinCEN. It is due on 15 April after the calendar year, with an automatic extension to 15 October. That is the rule on the IRS FBAR page. You must file one if your foreign accounts together exceeded $10,000 at any time in the year.

The end of the UK tax year on 5 April

The UK tax year closes on 5 April. Pension contributions, ISA subscriptions and gifts for a UK year must be made by then. Therefore, early April is a good time to collect payslips, P60s and statements for the UK year just ended. Those same records also feed the US return for the calendar year in progress.

What falls due between May and September?

The middle of the year brings the US extension date of 15 June and two US estimated payments. It also brings the second UK payment on account and, for some, Making Tax Digital updates. US UK cross border tax compliance does not pause for summer.

The automatic extension to 15 June for Americans abroad

Americans living abroad on the regular due date get an automatic two-month extension to 15 June. IRS Publication 54 sets out this rule for citizens and residents abroad. However, the extension is to file, not to pay. Interest runs on any unpaid tax from 15 April.

The second UK payment on account on 31 July

Payments on account are advance payments towards your next UK tax bill. The GOV.UK payments on account page says they are due by midnight on 31 January and 31 July. Each one is usually half of the previous year's bill. As a result, July is often a large payment month for self-employed Americans and landlords.

Quarterly updates under Making Tax Digital

Making Tax Digital for Income Tax is HMRC's system of digital records and quarterly updates for sole traders and landlords. HMRC's guidance on when to use it sets the start date by earlier income. If your qualifying income in 2024 to 2025 was over £50,000, you should have started from 6 April 2026. Lower thresholds bring others in from April 2027 and April 2028. HMRC's page on sending quarterly updates gives deadlines of 7 August, 7 November, 7 February and 7 May.

The US estimated payments in June and September

The second and third US estimated payments fall on 15 June and 15 September. If a date falls on a weekend or holiday, the payment is on time the next business day. In our experience, most employees in the UK do not need estimated payments. Nevertheless, landlords and people with large investment income often do.

What falls due between October and December?

Autumn brings the UK registration date and the US extended deadline in October. It also brings the UK paper return deadline and, by letter, a final US extension to 15 December. For many people, autumn is when last year is finally closed.

Registering for UK Self Assessment by 5 October

First-time filers must tell HMRC by 5 October after the end of the tax year. That is the rule on the deadlines page. You can register for Self Assessment online. Americans who start letting property or freelancing in Britain often miss this step.

The extended US return and FBAR on 15 October

If you file Form 4868, you get extra time to file, to 15 October in total. The FBAR's automatic extension also ends on 15 October. Therefore, this is the latest standard date for both the US return and the FBAR. It is not a later date to pay.

The paper return and the December extension

The UK paper return is due by 31 October, three months before the online deadline. Separately, Publication 54 lets Americans abroad ask for more time, to 15 December. You write to the IRS with your reasons. The IRS only replies if it refuses. Accordingly, plan to have both returns in progress well before December.

Which forms make up a typical US UK cross border tax compliance year?

For most Americans in Britain, the core is a US Form 1040 with foreign tax credits and an FBAR. A UK Self Assessment return is added where one is required. Investments, companies and treaty claims add further forms.

Foreign tax credits and the exclusion

Form 1116 claims the foreign tax credit. It reduces US tax by UK tax paid. Form 2555 claims the foreign earned income exclusion instead. In many UK cases, the credit works better because UK tax rates are higher. However, the right choice depends on your income mix.

Form 8938 and PFIC forms

Form 8938 reports specified foreign financial assets, alongside the FBAR. The IRS comparison of Form 8938 and FBAR sets higher thresholds for taxpayers abroad. For single filers, they are $200,000 at year end or $300,000 at any time. For joint filers, the figures are $400,000 and $600,000. Separately, UK funds often need Form 8621 as passive foreign investment companies.

Treaty positions

The US-UK income tax treaty changes how some income is taxed, such as pensions. Relying on the treaty to change US tax may need Form 8833, the treaty-based return position disclosure. Our guide to the US-UK double taxation treaty explains the main articles.

Matching UK tax to the US year

IRS Publication 514 explains when foreign tax counts for the credit. Under the accrual method, UK tax generally accrues on the last day of the UK tax year, 5 April. Under the cash method, you claim it in the year you pay it. Consequently, the method you choose shapes how UK tax lines up with US income.

Keeping records that serve both returns

Good records make the two calendars manageable. Keep payslips, P60s, bank and ISA statements, and rental accounts for each UK tax year. In addition, note the highest balance of every account during each calendar year for the FBAR. Finally, keep a travel log, because days in each country can matter for residence on both sides. With these in one place, US UK cross border tax compliance becomes a routine rather than a scramble.

What happens if you miss a date

A missed UK deadline brings late filing penalties and interest from HMRC. A missed US deadline brings failure-to-file and failure-to-pay penalties, plus interest. Moreover, a missed FBAR can carry separate penalties. Therefore, if a date has already passed, file as soon as you can rather than waiting for the next cycle.

What does a full US UK cross border tax compliance year look like?

An example shows how the dates come together. It is an illustration, not a real client.

An example: a London landlord

Consider a typical case. Megan is a US citizen in London with a salary and a rented-out flat. Her UK tax on salary comes through PAYE, but her rental profit needs a Self Assessment return. She also holds a stocks and shares ISA with UK funds.

In January, Megan files her UK online return and pays her balance and first payment on account. In April, her US return and FBAR are due, but she relies on the June extension because she lives abroad. She pays any US tax by 15 April to avoid interest. In July, she makes her second UK payment on account. By October, her US return, Forms 1116 and 8621 and FBAR are filed. Each return uses the same rental figures, converted for the US side.

What the example shows

Megan's US UK cross border tax compliance year has a date in almost every quarter. The rental income appears on both returns, on different year bases. Therefore, preparing both from one file avoids the mismatches that lead to letters from either tax authority.

The example also shows where the pressure points fall. January and October are the heavy months, because each closes a year on one side. By contrast, the summer dates are mostly payments. Knowing this in advance lets you gather papers once and use them twice.

How US UK Tax Experts can help

We prepare US and UK returns from one file, so the figures agree. First, we map your dates for the year, including any Making Tax Digital updates. Next, we prepare your Self Assessment return, your US return with foreign tax credits, and your FBAR. Finally, we flag the payment dates so nothing falls between the two calendars.

Our US federal returns service and UK Self Assessment service cover the core filings. For account reporting, see our guide to FBAR and FATCA reporting. In our experience, US UK cross border tax compliance is far simpler when one team holds both returns.

Conclusion

In summary, US UK cross border tax compliance means tracking two tax years that never line up. The UK dates cluster around 31 January, 31 July, 5 October and 31 October. The US dates cluster around 15 April, 15 June, 15 October and 15 December, with estimated payments between. Above all, a single calendar for both sides keeps you clear of late penalties and interest.

Contact us

Would you like one calendar and one team for both returns? Email us at hello@usuktaxexperts.com, or tell us about your situation through our contact page. We reply within one working day with the dates that apply to you and what we would need.