US UK Cross Border Tax Accountant: When You Need One and What They Prepare

US UK cross border tax accountant: an introduction

You need a US UK cross border tax accountant when you owe returns to both the IRS and HMRC and the two returns affect each other. That covers most Americans living in Britain, and many Britons with US income, property or family ties. One person or team then prepares both returns from the same figures. As a result, the tax credits, treaty claims and foreign account forms line up.

This article explains when you need that help, what the yearly work covers and which interactions are most often missed. Our full guide to US and UK tax returns prepared together walks through both returns in more depth.

What a US UK cross border tax accountant does

A cross-border tax accountant is a preparer who works on both tax systems at once. They build your US return and your UK Self Assessment return from one file. Furthermore, they check that income, tax paid and exchange rates match across the two. A single-country preparer, by contrast, usually treats the other country's return as somebody else's problem.

Why the two returns depend on each other

The US taxes its citizens on worldwide income wherever they live. The IRS states this plainly on its page for US citizens and resident aliens abroad. Meanwhile, the UK taxes its residents on their income too. Consequently, the same salary, interest or gain often appears on both returns. Relief in one country depends on the tax figures in the other.

Who needs a US UK cross border tax accountant?

You need one if you file in both countries, or if one country's rules change the answer in the other. The commonest cases are Americans working in the UK, dual nationals, and families with accounts, pensions or property on both sides.

Americans living and working in Britain

An American employed in London usually pays UK tax through PAYE. However, they still file a US return every year. If they have savings interest, rental income or self-employment income, they may also file UK Self Assessment. In that position, a US UK cross border tax accountant keeps the two filings consistent and claims the right relief on the US side.

Dual citizens and accidental Americans

Dual citizens born in the US but raised in Britain often learn late that they have US filing duties. Similarly, children of American parents can hold US citizenship without ever living there. These people usually need catching up as well as yearly returns. Our article on what to do if you haven't filed US taxes living in the UK covers the first steps.

Britons with US income or assets

The traffic runs both ways. A UK resident with US rental property, a US brokerage account or US pension income must report it to HMRC. In addition, some US income carries US filing duties of its own. Therefore, a Briton with American assets may need someone who understands both systems as much as an expat does.

Families moving between the two countries

The year you move is the hardest to get right. Your UK residence turns on the statutory residence test, explained in HMRC's guidance note RDR3. Furthermore, the US year runs January to December while the UK year runs April to April. A move mid-year therefore splits income across two different calendars.

What does a US UK cross border tax accountant prepare each year?

Each year, the core work is a US federal return, a UK Self Assessment return where one is due, and the foreign account forms the US requires. Around that sit treaty claims, credit calculations and any special forms your assets trigger.

The US federal return and its deadlines

Your US return is normally due on 15 April. However, US citizens living abroad get an automatic two-month extension to 15 June. Interest still runs on unpaid tax from 15 April. Additionally, Form 4868 extends the filing date to 15 October, as IRS Publication 54 explains.

The UK Self Assessment return

The UK tax year runs from 6 April to 5 April. For the 2025 to 2026 year, the online return is due by 31 January 2027, according to the Self Assessment deadlines page. Newcomers must register for Self Assessment by 5 October after the year ends. Moreover, many filers make payments on account on 31 January and 31 July.

FBAR and Form 8938

An FBAR is the annual report of foreign financial accounts that US persons file with FinCEN. You must file one if your foreign accounts together exceed $10,000 at any time in the year, as FinCEN explains. Separately, Form 8938 applies at higher thresholds. For an unmarried taxpayer living abroad, the Form 8938 instructions set them at more than $200,000 at year end or $300,000 at any time. Our guide to FBAR and FATCA reporting covers both forms.

Information returns for UK assets

UK investments often bring extra US forms. For example, Form 8621 reports holdings in passive foreign investment companies, which commonly include UK funds. Owning a UK company can bring Form 5471. Each form has its own penalties for being missed. Consequently, a US UK cross border tax accountant starts every year by listing what you own, not just what you earned.

Which interactions do single-country accountants miss?

The most common gaps are the choice between foreign tax credits and the earned income exclusion, UK tax-free savings that are taxable in the US, pension treatment under the treaty, and sales of a home. Each one needs both countries' rules in view.

Foreign tax credit or earned income exclusion

The foreign tax credit, claimed on Form 1116, reduces US tax by the UK tax paid on the same income. The IRS explains it on its foreign tax credit page. Alternatively, the foreign earned income exclusion removes up to $130,000 of earnings for 2025 and $132,900 for 2026, per the IRS exclusion figures. Because UK rates are often higher, the credit frequently works better. Even so, the right choice depends on your income mix, so we model both ways.

ISAs and UK funds

An ISA is tax-free in the UK, but the US does not follow that treatment. As a result, interest, dividends and gains inside an ISA usually go on the US return. Furthermore, many UK funds are treated as passive foreign investment companies for US purposes. That status brings punitive default rules unless the right elections and forms are in place.

Pensions and the treaty saving clause

The US-UK income tax treaty contains a saving clause in Article 1(4). The saving clause is a rule letting each country tax its own citizens as if the treaty did not exist. However, Article 1(5) lists exceptions, including the deferral of tax on pension growth in Article 18(1). Whether a particular pension payment escapes US tax depends on which article applies. HMRC publishes the treaty on its USA tax treaties page.

Selling your home

A UK main home is often free of capital gains tax under private residence relief. By contrast, the US exclusion in section 121 is capped at $250,000 of gain, or $500,000 on a joint return. Therefore, a London home that has risen sharply in value can produce a US tax bill with no UK tax to credit against it. Our article on a US person selling UK property works through this in detail.

How do you choose a US UK cross border tax accountant?

Choose someone who prepares both returns, explains how each figure moves from one return to the other, and asks about every account and pension before starting. Check the basics as well, such as registration with the IRS and proper authorisation with HMRC.

Check how both returns are prepared

Ask whether one team prepares both returns, or whether the work is split between firms. Splitting is not wrong, but somebody must reconcile the figures. Otherwise, you may claim credit in the US for UK tax that differs from the UK return. In our experience, that mismatch is one of the commonest problems we correct. Exchange rates are another, because the two returns can use different rates for the same income unless someone checks.

Check IRS and HMRC requirements

Anyone paid to prepare US federal returns must hold a valid preparer tax identification number. The IRS sets out the rule on its PTIN requirements page. It also gives guidance on choosing a tax professional. In the UK, you authorise an agent to deal with HMRC, as described in HMRC's guidance on authorising an agent.

Ask the right first questions

A good first conversation covers your citizenship, your residence history and every account, pension and property you hold. It should also cover any years not filed. If a preparer only asks about your salary, that is a warning sign. Likewise, a preparer should ask for last year's returns from both countries before starting. Indeed, a US UK cross border tax accountant earns their keep on the questions you did not know to ask.

What changes when your situation changes?

New residence, a new job, a business or a large gift can each add filings. A cross-border preparer reviews these events as they happen, rather than discovering them at the deadline.

Arriving in the UK under the new regime

From 6 April 2025, the UK replaced the remittance basis with a four-year foreign income and gains regime. It applies to people who were non-resident for the previous ten consecutive tax years. Under it, qualifying foreign income and gains can be relieved from UK tax for up to four years. However, claiming it has knock-on effects for the US foreign tax credit. HMRC's page on tax on foreign income explains the wider rules.

Working for yourself or starting a company

Self-employment brings National Insurance in the UK and possibly self-employment tax in the US. The two countries have a social security agreement to stop double contributions. HMRC issues a certificate of coverage to confirm which system you pay into. Starting a UK company adds further US forms, which our guide for founders and executives covers.

An illustrative example

Consider a typical case. Megan is a US citizen who moved to Manchester four years ago. She earns a salary through PAYE, holds a stocks and shares ISA and pays into a workplace pension. Her previous preparer in Ohio filed her US return using the earned income exclusion. Nobody filed an FBAR, and nobody looked at the funds inside her ISA.

A US UK cross border tax accountant would start by listing her accounts and funds. They would then compare the credit with the exclusion for her salary, add the ISA income to the US return and prepare FBARs. If earlier years were missed, they would look at the streamlined route. Finally, her UK return and US return would be built from the same figures each year.

How US UK Tax Experts can help

We prepare US and UK returns together from one file, so the two agree. First, we review your citizenship, residence and everything you own on both sides. Next, we prepare your US federal return and your UK Self Assessment return, with the FBAR and other forms that apply. We also handle UK funds through our PFIC reporting service.

If you are comparing options, our article on what US UK tax experts prepare explains how an engagement runs. We prepare and file; we do not give investment or financial advice.

Conclusion

In summary, you need a US UK cross border tax accountant whenever your US and UK returns affect each other. That is the case for most Americans in Britain and many Britons with US assets. The value lies in the interactions: credits, ISAs, funds, pensions and home sales. Above all, choose someone who prepares both returns from the same figures and asks about everything you own.

Contact us

Are you looking for a US UK cross border tax accountant to take on 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 filings that apply to you.