Cross Border Tax Specialists for US and UK: When to Hire One and When You Don't Need To

You should hire cross border tax specialists for US and UK returns when the two tax systems start to interact: the year you move, UK funds held by a US person, pensions, a property sale, a business across the border, or years that were never filed. If your affairs sit mostly in one country and your income is taxed at source, you can often file yourself.

That is not the answer a tax firm usually leads with, but it is the accurate one. Many people with ties to both countries have a routine year: a salary in one country, ordinary bank accounts, a workplace pension. The work in a routine year is known and repeatable. The work in an interacting year is not, and that is where specialist help earns its fee.

This guide sets out both sides: when you probably do not need a specialist, the nine situations where you probably do, and a short test to decide.

When you probably don't need a cross-border specialist

Three profiles often manage without specialist help.

A UK national with no US connection beyond a holiday or a US shareholding held through a UK platform. Someone who is not a US citizen, green card holder or US resident generally has no US return to file. UK tax is the whole picture.

An American in the UK with a simple, stable year. The IRS is clear that US citizens abroad are subject to tax on worldwide income, so a US federal return is due each year where the filing threshold is met, and benefits such as the foreign earned income exclusion and the foreign tax credit are claimed on that return. Where the aggregate value of foreign financial accounts exceeded $10,000 at any time during the calendar year, an FBAR is also required, filed electronically through FinCEN's BSA E-Filing System rather than with the tax return. For someone whose income is a UK salary taxed through PAYE, with UK current and savings accounts and a workplace pension, that is a repeatable annual routine many people handle with software.

A Brit living in the US for a short, planned period with no UK income. Where there is no UK income and no UK return, the work is on the US side only.

Two cautions. First, the UK side of a "simple" year is not always simple for a US citizen: GOV.UK lists foreign income, savings interest and dividends among the untaxed income that can require a Self Assessment return, so US bank interest or US dividends can bring a UK return into play. Second, routine years stop being routine. The triggers below are worth reviewing every year.

When should you hire cross border tax specialists for US and UK work?

Hire a specialist when your tax position depends on how the two systems treat the same income, asset or event. The table sets out the nine situations that most often cause trouble and why a single-country approach tends to miss them.

Situation	Why it is a cross-border problem	What tends to go wrong
1. The year you move between the countries	UK residence for that tax year turns on the statutory residence test; US residence starts or continues on different rules and a different calendar	Income taxed twice, or relief claimed in the wrong year
2. UK funds or an ISA held by a US person	Many UK collective funds are passive foreign investment companies (PFICs) for US purposes, reported on Form 8621	ISA wrappers treated as tax-free on the US return
3. Drawing or transferring a pension	Treaty treatment differs by type of pension and type of payment	A lump sum taxed in one country and not relieved in the other
4. Selling a home or rental property	Each country has its own rules on gains, exemptions and currency	A gain exempt in one country but taxable in the other, found late
5. A business or self-employment across the border	Business profits, social security and entity classification all interact	A UK company or US LLC treated differently by the two systems
6. Years that were never filed	US filing and FBAR obligations apply to US citizens abroad regardless of UK tax paid	Filing forward without dealing with the past
7. An inheritance or gift	Estate, inheritance and gift rules differ, as do the reporting forms	A foreign gift or inheritance left unreported on the US side
8. Giving up US citizenship or a green card	Exit rules apply on expatriation, with their own forms	A status change that is not complete for tax purposes
9. Significant foreign financial assets	Form 8938 applies on top of the FBAR above its thresholds	Only one of the two reports filed

If one of these applies this year, specialist help is usually worth at least a conversation. If two or more apply, a joint US and UK review is the safer course. Our cross border tax specialists for US and UK service page describes what that review covers.

The two triggers people underestimate

UK investments held by a US person. An ISA is tax-free in the UK. The US does not recognise the ISA wrapper, and the funds inside it are often PFICs. The IRS requires Form 8621 from US shareholders of PFICs in specified circumstances, including when they receive certain distributions or recognise a gain on disposal. We explain the mechanics in ISAs, PFICs and US tax.

Foreign financial assets above the Form 8938 thresholds. For taxpayers living abroad, the IRS sets the Form 8938 thresholds at more than $200,000 on the last day of the tax year or more than $300,000 at any time during the year for single filers, and more than $400,000 or $600,000 for married couples filing jointly. Form 8938 is attached to the income tax return and is separate from the FBAR, so many people need both.

Can you do US and UK taxes yourself?

Yes, and many people do. Neither the IRS nor HMRC requires you to use an adviser. The useful question is narrower: can you list every return and report your year requires in both countries, and do you know how income taxed in one country is relieved in the other?

Run this test before the next deadline:

1. List your returns. US federal return, any US state return, UK Self Assessment if required.
2. List your reports. FBAR if your foreign accounts exceeded $10,000 in aggregate at any time; Form 8938 if you are above its thresholds; Form 8621 if you hold PFICs.
3. Check this year against the nine triggers. A move, a sale, a pension event or a new business changes the answer.
4. Check prior years. Were all earlier US returns and FBARs filed?
5. Check the dates. For the 2025 to 2026 UK tax year, GOV.UK sets 5 October 2026 as the date to tell HMRC you need to file if you have not filed before, 31 October 2026 for paper returns and 31 January 2027 for online returns and payment. On the US side, Americans abroad have an automatic extension to 15 June, with interest running on unpaid tax from 15 April, and can extend to 15 October on Form 4868.

If you finish the list with every item answered, you are probably fine on your own. If you stop at any step unsure, that is the point where a specialist is useful. You may only need a one-off review, not an annual engagement.

What if you have already missed years?

If you have missed years, the usual route for US citizens living abroad is the streamlined foreign offshore procedures, which the IRS offers where the failure to report was non-willful. The IRS defines non-willful conduct as negligence, inadvertence or mistake, or a good-faith misunderstanding of the law.

Under the procedures, you file delinquent or amended US returns for the most recent 3 years whose due date has passed, and FBARs for the most recent 6 years. For US citizens and green card holders the non-residency test requires, in at least one of the last three years, no US abode and at least 330 full days physically outside the United States. The procedures are not available to someone already under IRS civil examination or criminal investigation.

This is a specific and consequential decision, and the certification of non-willfulness is signed by you. It is one of the clearest cases for specialist help. Our guide to the streamlined procedures sets out the steps.

Illustrative example: an American moved to Leeds six years ago on a UK salary and assumed that paying UK tax through PAYE covered everything. A new UK employer's onboarding prompts a question about US filings. Their situation hits two triggers: missed years, and a stocks and shares ISA holding UK funds. Filing the current year alone would leave the past untouched and misreport the ISA. The right sequence is to establish non-willfulness, prepare 3 years of returns and 6 years of FBARs under the streamlined procedures with the ISA funds analysed for PFIC reporting, and then carry on with a routine that fits.

What people get wrong about when to hire help

Assuming UK tax paid means nothing is owed to the US. Often nothing is owed, because credits and exclusions offset US tax. But the US return and the reports still have to be filed to claim them.

Hiring help after the event rather than before it. Most of the triggers are planned: a move, a sale, a pension withdrawal. Advice before the event can change the outcome. Advice afterwards can only report it.

Treating a one-country adviser as a two-country adviser. A good UK accountant with American clients may not prepare US returns. Ask which returns the firm itself files. Our article on tax specialist credentials for US/UK work explains what to look for, and accountants for US and UK taxes compares one firm with two.

Waiting for a letter. The cost of fixing a problem rises once a tax authority has raised it. Whether you remain eligible for the streamlined procedures, for example, depends on no examination having started.

How a first conversation should work

If you decide you need help, the first conversation should be about scope, not a sales pitch. Bring a list of your accounts, pensions, property and income in both countries, and what was filed in earlier years. A specialist should come back with the returns and reports your year requires, what is out of scope, and a fee against that scope. Our guide on how to choose US/UK cross border tax specialists lists the questions to ask.

US/UK Cross Border Tax — US CPAs and UK tax advisers working as one team; London, Manchester, New York, San Francisco. If you are planning a move, our moving abroad page covers the year of the move. If you are not sure which side of the line you are on, send us a short summary and we will tell you whether you need us.