Do I need separate accountants for my US and UK tax returns?

No. You can use separate preparers, but it is not required and often creates coordination problems. The US return relies on UK tax figures for the foreign tax credit, and the UK return can rely on US tax charged on US-source income for Foreign Tax Credit Relief. When one team prepares both returns from a single data set, income is assigned to the correct tax year in each country, one currency policy is applied, and treaty positions match. For higher-income households with investments on both sides, a single coordinated team reduces the risk of double taxation, missed credits and inconsistent filings.

Do Americans living in the UK still have to file a US tax return?

Yes. The United States taxes citizens and green card holders on worldwide income regardless of where they live, so an American resident in the UK generally files a US Form 1040 every year in addition to any UK Self Assessment return. Filing does not usually mean paying twice. UK income tax can often be credited against US tax through Form 1116, or earned income can be excluded through Form 2555. Foreign account reporting such as FinCEN Form 114 and Form 8938 may also apply, even when no US tax is due.

Which return should be filed first, the US or the UK return?

There is no fixed rule. The US return for a calendar year is due on 15 April, with an automatic extension to 15 June for citizens living abroad, while the UK online return is due on 31 January after the UK tax year ends on 5 April. Because the years overlap, the US foreign tax credit may need UK figures, and UK relief may need US tax figures on US-source income. The right sequence depends on your income mix, which is why coordinated preparation of both returns in parallel works better than waiting on another firm.

How does the UK tax year affect my US foreign tax credit?

The UK tax year runs from 6 April to 5 April, while the US tax year is the calendar year, so each UK return spans two US returns. IRS Publication 514 states that the credit is claimed by reference to your US tax year. Taxpayers can elect on Form 1116 to claim foreign tax in the year it accrues, and once made the election applies to all later years. If a UK liability later changes, the US credit may need to be redetermined on an amended return, so both returns must be tracked together.

Are ISAs tax-free for US citizens living in the UK?

ISAs are free of UK tax, but the IRS does not recognise the ISA wrapper. Interest, dividends and gains inside an ISA are generally reportable on the US return, and UK-domiciled funds held in an ISA are often passive foreign investment companies requiring Form 8621, which carries punitive default tax treatment. ISA balances also count toward FBAR and Form 8938 thresholds. Because the account is favourable in one system and potentially costly in the other, both returns should be considered before investing through an ISA as a US person.

What changed for Americans in the UK from 6 April 2025?

GOV.UK guidance confirms that the remittance basis was abolished from 6 April 2025. UK residents are now taxed on worldwide income and gains as they arise, subject to the 4-year foreign income and gains regime for qualifying new residents who have been non-resident for at least ten consecutive years. Claiming the regime removes the income tax and capital gains tax allowances for that year, and it has no effect on US tax. For a US citizen, the benefit of a claim should be tested against both returns before it is made.

Accountants for US and UK: One Firm for Both Returns

Accountants for US and UK tax are firms that prepare both your US federal return and your UK Self Assessment return as one coordinated file, so the income, foreign tax credits, currency conversions and treaty positions on each return agree with the other. For a US citizen or green card holder living in the UK, that coordination is the difference between paying tax once and quietly paying it twice. If your affairs include bonuses, investment portfolios, a UK company or accounts on both sides of the Atlantic, one team handling both returns is the most reliable way to keep the IRS and HMRC filings consistent.

What do accountants for US and UK returns actually do?

US UK tax returns preparation is the annual process of preparing and filing a US Form 1040 with its international information returns, and a UK Self Assessment return with HMRC, for the same individual, using one set of source figures. A dual-jurisdiction preparer does three things a single-country preparer cannot. First, it builds one master record of income, gains and taxes paid, then maps that record onto two different tax years. Second, it decides which country has the primary right to tax each item under the US-UK income tax treaty and claims relief in the correct country, in the correct order. Third, it applies one currency conversion policy and one set of documentation across both filings, so either tax authority could examine the file and find the same story.

For a high-net-worth household, the returns themselves are rarely the hard part. The hard part is the interaction: a foreign tax credit on the US return depends on UK tax figures that may not be final, and relief on the UK return can depend on US tax actually charged on US-source income. When two preparers each see only half of the picture, those dependencies are where errors sit.

Why does a US person living in the UK file two returns every year?

The United States taxes its citizens and green card holders on worldwide income wherever they live. The UK taxes its residents on their income and gains, and since 6 April 2025 GOV.UK guidance confirms that UK residents are taxed on the arising basis on worldwide income and gains, subject to the new 4-year foreign income and gains regime for qualifying new residents. The remittance basis, which many long-term American residents once relied on, was abolished from that date.

The result is that most Americans in the UK are within the scope of both systems at once. Filing in both countries does not usually mean paying tax in both countries. Relief comes from the US foreign tax credit, the foreign earned income exclusion, UK Foreign Tax Credit Relief and the treaty. But every one of those reliefs is claimed on a return, and each return has to be prepared with the other one in view.

What goes into the US side of the return?

For an affluent American in the UK, the US compliance package is usually much more than a Form 1040. Depending on the facts, it can include:

Form 1040, the individual income tax return, reporting worldwide income in US dollars.
Form 1116, the foreign tax credit, which credits UK income tax against US tax on the same income, generally computed separately for passive and general category income.
Form 2555, the foreign earned income exclusion. IRS guidance sets the maximum exclusion at $130,000 for 2025 and $132,900 for 2026, but for higher earners in the UK the foreign tax credit is often the stronger choice because UK rates are generally higher.
FinCEN Form 114 (the FBAR), required when the aggregate value of your foreign financial accounts exceeded $10,000 at any time during the calendar year. It is filed electronically through FinCEN's BSA E-Filing System, not with the tax return.
Form 8938, which IRS guidance requires for taxpayers living abroad when specified foreign financial assets exceed $200,000 on the last day of the year or $300,000 at any time (single or married filing separately), or $400,000 and $600,000 for married couples filing jointly.
Form 8621 for interests in passive foreign investment companies, which catches most UK-domiciled funds and many ISA holdings.
Form 5471 where you are an officer, director or shareholder of certain foreign corporations, including many UK limited companies owned by American founders and consultants.
Form 8833 where you take a treaty-based return position that must be disclosed.

What goes into the UK Self Assessment for an American?

The UK Self Assessment return reports income and gains for the UK tax year, which GOV.UK defines as 6 April to 5 April the following year. For an American resident in the UK, it typically covers employment income and benefits, bonuses, UK and foreign dividends and interest, capital gains on UK and US investments, rental income, self-employment or partnership profits, and the foreign pages where US-source income and US tax paid are declared. If you are new to the UK, it is also where a claim under the 4-year foreign income and gains regime is made.

GOV.UK guidance on foreign income explains that you can usually claim Foreign Tax Credit Relief on the Self Assessment return when you report overseas income, with the amount of relief determined by the double taxation agreement and capped where the income would have been taxed at a lower rate in the UK. For a US citizen, that means the UK return often needs the final US tax figure on US-source items such as US dividends or US rental income before it can be completed correctly.

Where do separate US and UK preparers go wrong?

Two competent preparers working independently can each produce a technically defensible return and still leave the client overpaying, under-reporting or holding contradictory positions. These are the failure points we see most often when a client arrives with one preparer in each country:

Tax-year mismatch: income is allocated to the wrong year because the UK year runs 6 April to 5 April and the US year runs 1 January to 31 December.
Foreign tax credit timing: the US return claims UK tax before the UK liability is final, or claims it in the wrong year, or never updates it when the UK figure changes.
Currency inconsistency: one return uses a yearly average rate, the other uses spot rates, so the same bonus appears as two different amounts and the credit calculation drifts.
Treaty positions taken on one return but not reflected on the other.
Divergent treatment of ISAs, UK funds and US funds, which are tax-favoured in one system and penalised in the other.
Missed or crossed deadlines, especially where the UK preparer is waiting for US figures and the US preparer is waiting for UK figures.

How does the tax-year mismatch create problems?

The UK tax year straddles two US tax years. A single UK Self Assessment return for 2025-26 covers income from 6 April 2025 to 5 April 2026, which falls partly into the US 2025 return and partly into the US 2026 return. Every salary payment, bonus, dividend and disposal must therefore be dated and assigned to the right year in each system. IRS Publication 514 makes clear that for foreign tax credit purposes, tax year means the year for which your US return is filed, not the year of your foreign return.

With two preparers, the US side usually works from a P60 and a year-end brokerage statement and has to guess how UK tax is split across calendar months. A combined team works from payroll records and transaction-level data, so the split is evidenced rather than estimated.

Why does foreign tax credit timing depend on both returns?

The foreign tax credit is only as good as the UK tax figure behind it. IRS Publication 514 explains that foreign taxes generally accrue on the last day of the foreign tax year for which the foreign return is filed, and that a cash-method taxpayer can elect to claim the credit when taxes accrue by checking the accrued box on Form 1116 on a timely filed original return. Once made, that choice binds all later years. For a UK resident, the accrual election often matches UK tax to the right income far better than the cash method, but it has to be chosen deliberately and kept consistently.

When the UK liability later changes, for example after an amended Self Assessment or a revised bonus allocation, Publication 514 describes a foreign tax redetermination, which generally requires an amended US return on Form 1040-X and a Schedule C (Form 1116) summary with the current-year return. Separate preparers rarely track these redeterminations, because the UK preparer does not know the change affects the US return. Unused foreign tax that exceeds the credit limit can be carried back one year and forward ten years, which is valuable only if someone keeps the carryover schedule accurate year after year.

Why must both returns use a consistent currency policy?

IRS guidance on foreign currency requires every amount on a US return to be expressed in US dollars, using the exchange rate prevailing when you receive, pay or accrue the item. Publication 514 adds that accrual-basis foreign tax credits generally use the average exchange rate for the tax year to which the taxes relate, while other taxes use the rate on the date paid or withheld. Meanwhile the UK return must convert dollar income into sterling.

A consistent currency policy is a written, year-on-year rule for which rate applies to which item on both returns. Without one, the same UK bonus can be translated at a spot rate on the US return while its UK tax is translated at an average rate, which distorts the credit. On the UK side, gains on US securities are computed in sterling, so a disposal that shows a dollar gain can produce a sterling loss or a much larger sterling gain than the US return suggests. A combined team makes sure the reconciliation between the two is deliberate and documented.

What happens when treaty positions do not match?

The US-UK treaty allocates taxing rights for employment income, dividends, interest, pensions and gains, and it contains a saving clause that generally preserves the right of the United States to tax its own citizens. Where a return relies on a treaty article to override the normal rules, Form 8833 is used to disclose the treaty-based return position. The risk with two preparers is an asymmetric position: the UK return treats an item as UK-taxable and claims relief for US tax, while the US return treats the same item as US-source and claims no credit, or both sides claim the primary right and neither gives relief. UK pension arrangements must also be described the same way on both filings.

How do ISAs, UK funds and PFICs get treated differently?

ISA income and gains are free of UK tax, so a UK preparer may not report them at all. The IRS does not recognise the ISA wrapper, so the income and gains inside it are generally taxable on the US return, and UK-domiciled funds held inside it are frequently passive foreign investment companies reportable on Form 8621 under a regime designed to be punitive. The reverse also happens: US mutual funds and ETFs held in a US brokerage account are ordinary investments for the IRS but can face less favourable treatment under the UK offshore fund rules.

A combined team builds one investment policy for both returns, identifying which holdings are efficient in both systems and which are efficient in one and costly in the other, so that portfolio decisions are made with both tax outcomes visible.

How has the end of the remittance basis changed the coordination?

For Americans who arrived in the UK recently, the 4-year foreign income and gains regime is now a key decision on the UK return. GOV.UK guidance states that a qualifying new resident, meaning someone in their first four years of UK residence after at least ten consecutive years of non-residence, can claim relief on chosen foreign income and gains through Self Assessment, but claimants give up the tax-free allowances for income tax and capital gains tax for that year.

For a US citizen, US-source investment income is foreign income to the UK. Claiming FIG relief can remove UK tax on that income, but it does nothing for US tax, and it may reduce the UK tax available to credit against US tax on other income. Whether the claim saves money overall can only be tested by modelling both returns together. A UK-only preparer will usually evaluate it in isolation.

Worked scenario: a London banker with two preparers versus one team

The following scenario is illustrative only, with rounded hypothetical figures, to show how coordination changes the outcome. Consider a US citizen working as a managing director at an investment bank in London, married to a non-US spouse, filing as married filing separately in the US.

Salary of £350,000 paid evenly through the UK tax year, and a £200,000 bonus paid in March 2026.
A US brokerage account holding US index funds, producing dividends and a sizeable gain on a sale in September 2025.
A stocks and shares ISA holding UK-domiciled funds.
UK bank accounts and the ISA pushing total foreign financial assets well above the Form 8938 and FBAR thresholds.

With two preparers, the UK preparer files the 2025-26 Self Assessment in January 2027 including the March 2026 bonus. The US preparer, who filed the 2025 US return in June 2026, never saw the bonus, which correctly belongs to the US 2026 year. For 2026, the US preparer receives a P60 covering April 2025 to April 2026, assumes the UK tax on it relates to calendar 2025, and credits it on an amended 2025 return, leaving 2026 with a large bonus and too little credit. The ISA funds are omitted from the US return entirely, no Form 8621 is filed, and the September gain is translated at a year-end rate on the US return while the UK computes it in sterling using transaction-date rates.

With one team, the bonus is assigned to the US 2026 year and the UK 2025-26 year from payroll records, UK tax is accrued to the correct US year under a consistent accrual election, the ISA fund holdings are analysed for PFIC reporting before the first filing, and one currency schedule supports both the US gain and the UK computation. The result is not a lower headline tax rate. It is a pair of returns where the credits match the income, nothing is double counted, and nothing is omitted.

How do the US and UK deadlines fit together?

The two calendars interlock, and a combined engagement plans the sequence rather than reacting to it. The key dates, as published by the IRS, FinCEN and GOV.UK, are:

15 April: US return and payment due for the prior calendar year; FBAR due, with an automatic extension to 15 October.
15 June: automatic two-month extension to file for US citizens living abroad who attach the required statement. The IRS charges interest on any tax not paid by 15 April.
31 July: UK second payment on account for the current year.
5 October: deadline to tell HMRC you need to file a Self Assessment return if you have not filed before.
15 October: US extended filing deadline where Form 4868 was filed; final FBAR deadline under the automatic extension.
31 October: UK paper return deadline.
31 January: UK online Self Assessment deadline and balancing payment, plus the first payment on account for the following year.

Because the UK return for a given year is not due until ten months after it ends, while the US return for the calendar year that contains the last three months of that UK year is due first, the order of preparation is a judgement call made case by case. Sometimes the UK figures are needed to finalise the US credit; sometimes the US tax on US-source income is needed to finalise UK relief. One team can run both in parallel instead of waiting on the other side.

Can past mismatches between the two returns be corrected?

Often, yes. IRS Publication 514 gives taxpayers 10 years to file a claim for refund where they paid or accrued more foreign tax than they claimed a credit for, and the same window applies to switching from a deduction to a credit. That makes a review of prior-year credits worthwhile for anyone who has used separate preparers. On the UK side, amendments and overpayment relief follow HMRC's own time limits, which we check individually for each year under review.

Where returns or FBARs were never filed, the IRS Streamlined Filing Compliance Procedures remain the recognised route for non-wilful taxpayers living abroad, and the eligibility conditions should be confirmed on IRS.gov at the time of filing. Clients should be cautious of older articles describing a separate delinquent FBAR submission route; IRS guidance on catching up has changed, and the current route should be confirmed before any late FBAR is filed.

What does a combined engagement with accountants for US and UK returns deliver?

A combined engagement with accountants for US and UK returns is a single annual mandate covering US federal compliance, FinCEN reporting and UK Self Assessment, prepared from one data set by one coordinated team. For our clients it delivers:

One master income and tax schedule mapped to both the UK and the US tax year.
A documented currency policy applied to both returns and repeated year on year.
Foreign tax credit computations reconciled to final UK liabilities, with carryovers and redeterminations tracked.
Consistent treaty positions, with Form 8833 disclosures where required.
FBAR, Form 8938, Form 8621 and Form 5471 reporting prepared alongside the income tax returns.
A single filing calendar covering every US and UK deadline and payment.
A review of prior years where separate preparers may have left credits unclaimed.

What documents should you gather for US and UK tax returns preparation?

To start a combined engagement, gather the following for the relevant UK tax year and both overlapping US calendar years:

Prior two years of US returns and UK Self Assessment returns, including HMRC calculations and statements of account.
P60, P11D and monthly payslips, plus bonus and equity award statements with vesting and payment dates.
Year-end and transaction statements for every UK and US bank, brokerage, ISA and investment account, with maximum balances for FBAR.
Fund factsheets or holdings lists for ISA and UK fund investments, for PFIC analysis.
Completion statements for property, and rental income and expense records.
Company accounts, share registers and corporation tax returns for any UK company you own or direct.
Your UK arrival date and residence history, for the statutory residence test and any FIG claim.
Any HMRC or IRS correspondence received during the year.

With that file in hand, one team can prepare both returns from the same numbers, so the IRS and HMRC see one consistent account of your income, and you pay the tax that is due once, in the right country.