Tax Specialists for US and UK: What They Do, Who Needs One and How to Choose

A tax specialist for US and UK matters is an adviser, or more often a team, that prepares and plans for both a US federal return and a UK Self Assessment return for the same person, applying the US/UK double taxation convention so that income is taxed once, credited correctly and reported to both the IRS and HMRC on time. The defining feature is not a job title. It is that the person signing your Form 1040 and the person signing your SA100 are working from one set of facts, with one view of your residence position, and are answerable to each other.

That matters because the two systems disagree on almost everything structural. The US taxes its citizens and green card holders on worldwide income wherever they live; the UK taxes by residence. The US tax year is the calendar year; the UK's runs from 6 April to 5 April. The US ignores UK tax wrappers such as ISAs; the UK, since 6 April 2025, has replaced the domicile concept with a residence-based regime that a US citizen must weigh against US rules before using. A generalist can be excellent at one side and still hand you an expensive problem on the other.

What "dual-qualified" actually means

Firms use the phrase loosely. Strictly, a dual-qualified individual holds a recognised US tax credential (a CPA licence from a state board, IRS Enrolled Agent status, or admission as a US tax attorney) and a recognised UK one (Chartered Tax Adviser from the CIOT, ATT, or a chartered accountancy qualification such as ACA or ACCA). A dual-qualified firm may instead have separately credentialed US and UK professionals who work as one team. Either can be right for you. What you should not accept is a UK accountant who "has a contact in the States", or a US preparer who has never opened HMRC's manuals.

Specialist versus a general accountant

The borderline cases are worked through in when you need cross border tax specialists and when you don't. If you are comparing firms rather than individual advisers, our guide to accountants for US and UK covers fees, the joint engagement and the documents to bring.

You need a specialist when both tax authorities have a genuine claim on the same income or asset in the same year and the answer to "who taxes what" depends on the treaty or on elections that have to be made correctly the first time. You probably do not need one if only one country can tax you and nothing you own is treated differently across the border. The table applies that test to common situations.

Americans in the UK

The US obligation never switches off. Every form is listed in what Americans living in the UK have to file, and there is more on how we work with Americans living in the UK; the real decision is which reliefs to combine. Most people in employment end up using the foreign tax credit rather than the foreign earned income exclusion because UK rates are higher, but the choice has knock-on effects for child tax credits and for future years, so it should be modelled rather than defaulted. Founders who own a UK company have a longer list, because the company brings its own US reporting.

Brits in the US

The traffic runs both ways. A British citizen who becomes a US resident is taxed by the US on worldwide income, including UK rental profits and UK pension growth in some cases, and may still owe UK tax on UK-source income as a non-resident; landlords who kept a UK property are the most common example. We cover how we help Brits living in the US separately, the tax guide for Brits moving to the US covers the first year, and the treaty's tie-breaker rules decide residence where both countries claim it.

Dual citizens, accidental Americans and green card holders

Citizenship, not address, drives the US side. Dual citizens file in both countries every year; an accidental American who has never filed usually has a clean route back through the Streamlined procedures, set out in tax for accidental Americans; a green card holder living abroad keeps US obligations until the card is surrendered properly, and surrendering it can itself have tax consequences.

The work falls into three layers: the US return, the UK return, and the coordination between them. The third layer is the reason to hire a specialist at all.

The US side

• Form 1040 and any state return. Some states, notably California, New York and Virginia, are reluctant to let residents go; a specialist checks state residency before you leave, not after. Our US tax return service covers federal and state filings.
• Form 1116 (foreign tax credit) or Form 2555 (foreign earned income exclusion). For 2026 the exclusion is $132,900, up from $130,000 for 2025.
• FBAR (FinCEN Form 114) when foreign accounts exceed $10,000 in aggregate at any point in the year, and Form 8938 when specified foreign assets exceed $200,000 at year end or $300,000 at any time for a single filer living abroad ($400,000 and $600,000 for joint filers). The difference is explained in FBAR versus Form 8938.
• Form 8621 for each UK fund, ISA holding or unit trust that is a passive foreign investment company. See why your ISA is a problem on a US return.
• Form 8833 to disclose a treaty-based position, most often on pensions. The rules are set out in when Form 8833 is required.
• Forms 5471, 8858 and 3520/3520-A for UK companies, foreign disregarded entities and branches, and UK trusts or large foreign gifts.

The UK side

• Self Assessment: the SA100 with the SA106 foreign pages, SA109 residence pages and SA105 property pages as required. Our UK Self Assessment service handles registration, the return and payments on account.
• Residence under the Statutory Residence Test, including split year treatment in the year you arrive or leave.
• The Foreign Income and Gains regime for qualifying new residents, claimed on the SA109 pages, and its interaction with US tax, which can make a claim cost more than it saves (more on that below).
• Making Tax Digital for Income Tax, which now applies to sole traders and landlords with qualifying income over £50,000 from 6 April 2026, dropping to £30,000 from April 2027 and £20,000 from April 2028. An American landlord in the UK is caught like anyone else.

The coordination layer

This is where the two returns talk to each other. The UK return for the year to 5 April is prepared first for a UK-resident client, because the UK tax it produces is what goes on Form 1116 for the overlapping calendar year. Exchange rates have to be applied consistently. Treaty positions taken on the US return, on a SIPP for example, must match what the UK return says about the same pension.

Account lists for FBAR and Form 8938 are built once and reused. Where an American is married to a non-US spouse, the spouse's own UK return should report joint accounts and household income consistently with the American's US return; there is no official term for this, though some advisers call it a "mirror return". None of this is difficult in isolation; the failures come from two advisers who never speak.

Specialists also handle the situations that sit outside annual compliance: Streamlined Foreign Offshore Procedures for people who have fallen behind, renunciation and the exit tax, property sales on either side, and the pension questions that arise when a SIPP meets a 401(k).

Three sets of changes have altered the advice for anyone with feet in both countries.

UK: domicile abolished, the FIG regime arrives

From 6 April 2025 the UK stopped using domicile for income tax and capital gains tax and replaced the remittance basis with a four-year Foreign Income and Gains regime. A "qualifying new resident", someone in their first four years of UK residence after at least ten consecutive years of non-residence, can claim relief from UK tax on foreign income and gains, but the claim removes the personal allowance and the capital gains annual exempt amount for that year. The mechanics are covered in our guides to the FIG regime and to what the non-dom changes mean for Americans.

For a US citizen the difficulty is plain: FIG relief removes UK tax on, say, US dividends, but the US still taxes them, and with no UK tax paid there is nothing to credit. In many cases claiming FIG simply moves the tax from HMRC to the IRS while costing you the personal allowance on your UK salary. It has to be modelled on both returns before any claim is made.

UK: inheritance tax now follows residence

Also from 6 April 2025, inheritance tax on worldwide assets applies to a long-term UK resident: someone UK resident for at least ten of the previous twenty tax years. The status persists for up to ten tax years after leaving, on a sliding scale. An American who has been in London since 2016 is now inside the UK inheritance tax net on their US assets, and the US estate tax regime has not gone anywhere. Our US/UK trusts and estates service deals with the overlap.

US: the 2025 and 2026 figures

The foreign earned income exclusion is $130,000 for 2025 and $132,900 for 2026. The 2026 standard deduction is $16,100 for single filers, $32,200 for married couples filing jointly and $24,150 for heads of household. The FBAR threshold remains $10,000 in aggregate. For tax years beginning after 31 December 2025, the regime formerly called GILTI is renamed net CFC tested income, which matters to any US citizen who owns a UK company. Anyone considering renunciation should check the current covered-expatriate tests on the IRS expatriation page; how the exit tax works is explained in renouncing US citizenship.

Letters after a name tell you which regulator stands behind the adviser and which tax authority they can represent you before. They do not tell you the person knows the other country's system. Use the table to decode what you are being offered, then verify it.

Two things the table cannot show. First, anyone who prepares US returns for a fee must hold an IRS Preparer Tax Identification Number and sign as paid preparer; ask who will sign your 1040. Second, HMRC does not license tax advisers, but since 18 May 2026 anyone paid to deal with HMRC on a client's behalf must register with HMRC as a tax adviser and meet its minimum standards, with existing agents registering in phased windows. Registration is not a qualification, so membership of a professional body (CIOT, ATT, ICAEW or ACCA), with its complaints process and insurance requirements, remains the main check of competence on the UK side.

The IRS's own page on preparer credentials sets out what each US designation allows, and CPA, EA, CTA and ATT credentials compared goes into more depth.

Why one credential is not enough

A CPA licence proves competence in US accounting and tax; it says nothing about the Statutory Residence Test or the SA109 pages. An ACA proves UK competence; it says nothing about Form 8621. The firm you choose needs both, held either by the same people or by people who sit on the same team and review each other's work. Ask how the two sides communicate on your file. If the answer involves email chains to a separate firm, you are paying for two advisers and getting the coordination of neither.

1. Onboarding call. Citizenship, visas, move dates, employer, accounts, pensions, property, businesses, and what has been filed where. This is where a specialist spots the FBAR you did not know about.
2. Residence determination. The UK Statutory Residence Test for the tax year, including any split year; the US tests for non-citizens; the treaty tie-breaker if both countries claim you. The result is written down and drives everything else.
3. Strategy decisions. Foreign tax credit or foreign earned income exclusion; whether to claim FIG relief; treaty positions on pensions; what to do about PFICs already held.
4. Document collection. Both columns of the checklist below, through a secure portal.
5. UK return first (for UK residents). The year to 5 April is finalised so the UK tax figure is real, not estimated.
6. US return. Form 1040 with 1116 or 2555, 8938, 8621, 8833 and any state return; FBAR filed separately through FinCEN's system.
7. Review and sign. One reviewer sees both returns together.
8. Filing and confirmations. HMRC submission receipt, IRS e-file acceptance, FBAR confirmation.
9. The year ahead. Payments on account, US estimated taxes if relevant, and a note of what to change before the next 5 April.

Which return is prepared first, and why

For a UK resident, the UK return. Its tax year ends on 5 April, so by the time the US return for the previous calendar year is due, the UK figures for nine months of that year are final and the remaining three can be closed. Preparing the US return first forces you to estimate the UK tax and amend later. For a US resident with UK income the order flips: the US return sets the credit position and the UK non-resident return follows.

The dual-country deadline calendar

Dates are from GOV.UK and the IRS page for citizens abroad. The edge cases are covered in separate posts on the US expat extension deadlines and the FBAR deadline.

Document checklist

These are illustrations of how the pieces fit, not client cases or advice. Every real situation turns on its own facts.

A software engineer from Chicago working in London on PAYE, with a stocks and shares ISA. UK tax on salary is higher than the US tax would be, so the foreign tax credit on Form 1116 eliminates the US liability on employment income. The ISA is invisible to HMRC but each fund inside it is a PFIC for the IRS, so Form 8621 is required per fund and the excess distribution rules can produce US tax even in a year with no UK tax. The specialist's advice is to restructure the ISA into holdings that are not PFICs, or to keep the funds knowing that each one adds a Form 8621 and US tax every year.

A British founder moving to New York with a UK limited company and a SIPP. On becoming US resident she owns a controlled foreign corporation, bringing Form 5471 and potential net CFC tested income (formerly GILTI) inclusions. The SIPP's growth is protected by Article 18 of the treaty, disclosed on Form 8833, and reported on FBAR and Form 8938. New York State will tax her from the day she arrives. Her UK return becomes a split-year return and then a non-resident one. See SIPP reporting on a US return.

A dual citizen in Manchester, born in Ohio, who has never filed a US return. Because the failure to file was non-wilful and he lives outside the US, the Streamlined Foreign Offshore Procedures allow three years of returns and six years of FBARs with a certification, and no penalty. The UK Self Assessment position is unchanged. The Streamlined procedures guide walks through the steps.

Fees for a coordinated US and UK engagement vary widely with complexity: a simple two-return year costs far less than a first year involving PFICs, a company or a Streamlined catch-up. What drives the fee is complexity, not income: the number of returns, the number of foreign accounts and funds, whether a state return is needed, how many years of catch-up are involved, and whether treaty positions have to be researched and disclosed.

Ask for a fixed fee in writing before work starts, with a list of what it includes. Hourly billing on cross-border work rewards the adviser for inefficiency. A fixed fee should cover the items listed in what tax preparation services for the US and UK include; for your own quote, tell us your situation.

Questions to ask before you engage

1. Who prepares the US return and who prepares the UK return, and do they sit in the same team?
2. Which of you holds a US credential, which holds a UK one, and can I verify both?
3. Who signs my Form 1040 as paid preparer, and do they have a PTIN?
4. How do you determine my residence position, and will you document it?
5. Will you model the foreign tax credit against the foreign earned income exclusion for my numbers?
6. How do you handle PFIC reporting for my ISA or UK funds?
7. Will you file Form 8833 for my pension, and what position will you take?
8. What is your process if HMRC and the IRS disagree on my residency?
9. Do you represent clients before both the IRS and HMRC if there is an enquiry?
10. What is the fixed fee, what does it include, and what is extra?
11. What is your turnaround during January and April, the two busiest months?
12. How many clients in my situation do you act for?

Red flags

• A UK fee quote without a single question about US citizenship or green cards.
• "Your ISA is tax free" with no mention of PFICs.
• Unfamiliarity with Form 8833 or Form 8621.
• Advice to skip the FBAR because "no tax is due".
• Claiming both the foreign earned income exclusion and a foreign tax credit on the same income.
• Treating National Insurance as creditable income tax on the US return.
• No written fixed fee, or a fee that cannot be explained.
• "We outsource the US side" with no named person.
• No professional body membership on the UK side, no PTIN on the US side.
• Promises of a zero tax outcome through structures they cannot explain.

Each of these is expanded in choosing US/UK cross border tax specialists, and comparing providers fairly gives a scoring sheet.

Almost none of this work needs a meeting room. Documents move through a secure portal, signatures are electronic, and both the IRS and HMRC accept electronic filing. What clients value is time-zone coverage and the option of sitting across a table for the decisions that matter: a renunciation, a company restructure, an estate plan spanning both countries.

US/UK Cross Border Tax — US CPAs and UK tax advisers working as one team — works from four offices: London at 4 Crown Place, Manchester at CORE on Brown Street, New York at 33 Irving Place and San Francisco at 600 California Street. A client in Leeds and a client in Austin get the same US CPAs and UK tax advisers on the same file. If you are outside all four cities, the process is identical.