Do I have to file a US tax return while working in the UK on a fixed-term contract?

Yes. US citizens are taxed on worldwide income regardless of where they live, so a Form 1040 covering your full calendar year is due once your income passes the normal filing thresholds. Living abroad gives you an automatic extension to 15 June, but not relief from filing. The Foreign Earned Income Exclusion and the Foreign Tax Credit are what stop the UK salary being taxed twice.

Does UK split-year treatment also split my US tax year?

No. Split-year treatment is purely a UK mechanism that limits which part of the move year the UK taxes. The United States still taxes a citizen on the entire calendar year, with no part-year return available. That mismatch is exactly why apportioning income and choosing between the exclusion and the credit matter so much in the arrival and departure years.

Can I claim the Foreign Earned Income Exclusion in my first year in the UK?

Often only partly. The bona fide residence test usually fails in the arrival year because that year is not a full tax year of UK residence, which leaves the 330-day physical presence test as your route. Even then the exclusion is pro-rated down to your qualifying days, so it rarely covers a full salary. Form 2350 can extend your filing deadline until you have met the 330-day count.

Will I pay both UK National Insurance and US Social Security on a secondment?

Not if the certificate of coverage is arranged correctly. The US-UK Totalization Agreement keeps a worker in one country's social security system at a time. A US employer posting you for up to five years can generally keep you in the US system with a certificate of coverage that exempts you from UK National Insurance; a direct UK hire normally pays National Insurance here instead.

Do I need to file an FBAR for a UK bank account I opened after moving?

Yes, if the combined high balance of all your foreign accounts exceeds $10,000 at any time in the year, which a salary account usually does. The FBAR is FinCEN Form 114, filed electronically and separately from your Form 1040. A fixed-term posting normally means a first FBAR in the arrival year and a final one in the year you leave.

Is the Foreign Tax Credit or the exclusion better for a fixed-term contract?

It depends on the numbers, but the Foreign Tax Credit is often stronger for a higher earner on a UK contract, because UK tax usually exceeds the US tax on the same income and the credit is neither pro-rated nor capped. The exclusion can still help lower earners or particular years. You cannot claim both on the same income, so the best split is modelled during preparation.

US UK Tax Returns Preparation: Fixed-Term Contract

US UK tax returns preparation changes shape the moment a US citizen signs a fixed-term UK contract, because the posting almost never lines up neatly with either country's tax year. A secondment or project role of one to three years drops you into the United Kingdom partway through a calendar year, lands you inside two tax systems that begin and end on different dates, and then, when the contract runs out, pulls you back across the Atlantic mid-year again. The arrival year and the departure year are where returns quietly go wrong, and they are exactly where coordinated preparation earns its keep.

The short version is that both returns are prepared as one exercise, not as two filings that happen to involve the same person. Your UK position is governed by the Statutory Residence Test and, in the years you move, by split-year treatment. Your US position never switches off, because an American is taxed on worldwide income and files a Form 1040 wherever in the world they happen to be living. The craft lies in making the two meet: choosing between the Foreign Earned Income Exclusion and the Foreign Tax Credit, apportioning income across mismatched tax years, and clearing the reporting duties a fixed term creates almost by accident.

What Does a UK Fixed-Term Contract Change About Your Two Returns?

A fixed term is defined by its edges. Unlike an open-ended emigration, a one to three-year contract has a known start date and a known end date, and both of them tend to fall in the middle of a tax year rather than tidily on 6 April or 1 January. That single fact drives most of the complexity. In the arrival year you are a part-year UK resident but a full-year US filer; in the departure year the position reverses on the UK side, while the US side, once again, covers the whole calendar year. Neither edge is a clean break.

It also matters that you are a citizen rather than a visa-holding foreign national. A non-citizen moving to or from the United States can often split their US year into resident and non-resident parts on a dual-status return. A US citizen gets no such relief. Washington taxes every one of your days, in Peoria or in Pimlico, so the whole job of preventing double taxation falls on treaty positions, the exclusion, the credit and careful timing, rather than on carving up the US year itself.

Are You UK Tax Resident Under the Statutory Residence Test?

The United Kingdom decides residence through the Statutory Residence Test, a day-counting framework that reads your year against three sets of rules in a fixed order. You look first at the automatic overseas tests, which can confirm you are not UK resident, usually on low day counts or genuine full-time work abroad. If none applies, you move to the automatic UK tests, which can make you resident outright, most commonly by spending 183 days or more in the UK in the tax year. Only if neither set settles the matter do you reach the sufficient ties test, which weighs the days you spend here against connecting factors such as family and accommodation.

The automatic overseas tests, which can establish non-residence, for example through very low UK day counts or genuine full-time work outside the UK
The automatic UK tests, which can establish residence outright, most often by being present for 183 days or more in the tax year
The sufficient ties test, applied only when the automatic tests do not decide it, balancing UK days against ties such as family, available accommodation, work and time spent here in earlier years
The day-counting conventions themselves, including how a day of presence is measured and the limited deemed-day and exceptional-circumstances rules that can adjust the count

How Does Split-Year Treatment Help in the Arrival and Departure Years?

UK residence is normally an all-or-nothing status for a whole tax year, which would be punishing for someone who arrives in September. Split-year treatment relaxes that. Where you meet one of its specific cases, the tax year is divided into a UK part and an overseas part, and you are taxed as a UK resident only for the portion after you arrive, or before you leave. The cases are prescribed rather than optional: they turn on events such as starting to have your only home in the UK, beginning full-time work here, or the mirror-image situations when you depart.

For a fixed-term contractor the relevant arrival cases usually hinge on starting full-time work in the UK or acquiring a home here; the departure cases hinge on leaving to work full-time abroad or ceasing to have a UK home. Split-year treatment is a UK mechanism only. It changes which slice of your income the UK taxes in the move years, but it has no effect whatsoever on the US side, and assuming that it does is one of the most common and most expensive misunderstandings in a first cross-border return.

Do You Still File a US Form 1040 While on a UK Contract?

Yes, without exception, provided your income clears the ordinary filing thresholds, which most professionals on a UK contract will. Citizenship, not residence, is the trigger for US tax, so the Form 1040 reports your worldwide income for the full calendar year, including the UK salary, any UK bank interest and any US-source income you keep. Living abroad buys you an automatic extension of the filing deadline to 15 June, with a further extension available on request, but it removes neither the duty to file nor the duty to report. What it offers instead is two mechanisms to stop the same income being taxed twice.

Can the Foreign Earned Income Exclusion Cover a Fixed-Term Posting?

The Foreign Earned Income Exclusion, claimed on Form 2555, lets you exclude a band of foreign wages from US tax, roughly $130,000 and indexed upward each year, often with a foreign housing amount on top that matters in a city as expensive as London. To reach it you must clear one of two gateways. The bona fide residence test asks whether you were a genuine resident of the UK for an uninterrupted period that includes a full US tax year. The physical presence test is purely mechanical: 330 full days outside the United States in any 12 consecutive months. The two tests are not interchangeable, and a fixed term tends to steer you toward the harder one.

Bona fide residence test: you are a settled resident of the UK for an uninterrupted period covering an entire US tax year, which a mid-year arrival on a fixed term usually cannot satisfy in the first calendar year
Physical presence test: 330 full days abroad within any 12-month window you choose, which you can meet in the arrival year, but only by watching your US trips carefully
Pro-ration: when your qualifying period covers only part of the US tax year, the maximum exclusion is scaled down by the number of qualifying days over 365, so an arrival-year exclusion is only a fraction of the headline figure
Timing relief: where you will pass the physical presence test only after the normal deadline, Form 2350 asks for extra time so you can file once you qualify rather than amend later

This is where a fixed term bites. A one-year posting may never include a full US tax year of UK residence at all, which can rule out bona fide residence entirely. The 330-day test is then your only route, and it is tight: a fortnight of US client meetings plus a two-week trip home for the holidays can tip you past the 35 days of permitted US presence and break it. And even when you do qualify, the arrival-year exclusion is pro-rated down to the days in your qualifying period, so it rarely shelters a full professional salary on its own.

Why Is the Foreign Tax Credit Often the Stronger Choice?

The Foreign Tax Credit, taken on Form 1116, works the other way around: instead of excluding income, it gives you a dollar-for-dollar credit against your US tax for income tax you actually paid to HMRC. Because UK marginal rates on a higher earner generally run above the equivalent US rates, the credit frequently wipes out the US tax on your UK salary completely and leaves an excess you can carry back one year and forward ten. For a fixed-term contractor it has three practical advantages over the exclusion: it is not pro-rated away in the move years, it is not capped at the exclusion ceiling, and it does not force the all-or-nothing day counting that the 330-day test demands. The two can be combined, but you cannot credit tax on income you have already excluded, so the split has to be modelled rather than guessed.

How Do You Reconcile the 5 April and 31 December Tax Years?

The United Kingdom runs its tax year from 6 April to 5 April; the United States runs on the calendar year to 31 December. Those two calendars never align, and the gap is the single most tedious part of preparation. UK employment income has to be re-cut onto a calendar-year basis for the Form 1040, and the UK tax used for your Foreign Tax Credit has to be matched to the US year in which the underlying income falls, which frequently means apportioning one UK tax year across two US returns. Converting everything into dollars at appropriate exchange rates, and keeping that apportionment consistent from year to year, is what keeps the credit defensible if the IRS ever looks closely.

Worked Example: An Arrival-Year Split, Pro-Rated FEIE Versus FTC

The following uses an invented person and round figures purely to show the mechanics; it is not a real case, and the exchange rate is assumed. Dana Whitfield, a US citizen, moves to London on 1 May 2026 to begin a two-year fixed-term contract paying £140,000 a year, about $182,000 at an assumed rate of 1.30. From arrival to 31 December she earns roughly $121,000 of UK salary. For UK purposes she claims split-year treatment, so the UK taxes her only from May. For US purposes her entire 2026 calendar year sits on the Form 1040 regardless of when she landed.

Take the exclusion route first. Dana meets the physical presence test using a 12-month period beginning on 1 May 2026, but because that qualifying period covers only 245 days of the 2026 calendar year, her maximum exclusion is pro-rated to roughly $130,000 times 245 over 365, about $87,260. Her in-period UK earnings of around $121,000 therefore leave approximately $33,700 of salary still exposed to US tax, which she must then shelter with the credit anyway. Bona fide residence is not open to her for 2026 at all, because 2026 is not a full tax year of UK residence.

Now the credit route. The UK tax Dana actually pays on that $121,000, at higher-rate marginal rates, comfortably exceeds the US tax on the same income. Claimed in full on Form 1116, it eliminates her US tax on the UK salary and leaves an excess credit to carry forward. The credit is neither pro-rated nor capped, so on these numbers it is the cleaner answer, and it keeps her out of the fragile 330-day count during a year when she may well need to fly back to the US for work. The exclusion still has its place, but for this fixed-term arrival year the Foreign Tax Credit does more, with less risk.

What About FBAR and Social Security on a Fixed-Term Posting?

Opening a UK current account on day one is usually unavoidable, and it quietly creates a US reporting duty. The FBAR, filed electronically as FinCEN Form 114, is required when the aggregate high balance of all your foreign financial accounts tops $10,000 at any point in the calendar year, even for a single day, and even if the money is only your salary passing through. It is an information report, not a tax, but the penalties for ignoring it are severe. A fixed-term arrival typically triggers a first FBAR in the arrival year and a final one in the departure year, and the balances of any UK savings or investment accounts opened during the posting have to be swept in too. A separate FATCA form, Form 8938, can also apply at higher thresholds.

Social security is governed by the US-UK Totalization Agreement, which exists precisely to stop a seconded worker paying into both countries' systems on the same earnings. If a US employer posts you to the UK on a contract expected to last no more than five years, you can generally stay in the US social security system and be exempted from UK National Insurance by obtaining a certificate of coverage from the US authorities. If instead you are hired directly by a UK entity, or the posting is expected to run beyond five years, you will normally pay UK National Insurance and be covered here. Securing the certificate at the outset, in the right direction, avoids a double charge that no income tax credit can recover.

US UK Tax Returns Preparation: Why the Arrival and Departure Years Decide Everything

Done well, US UK tax returns preparation for a fixed-term contractor is front-loaded. The decisions that determine whether the move years are clean or chaotic, the residence and split-year analysis, the exclusion-versus-credit choice, the certificate of coverage and the first FBAR, are all made best before or at the point of the move, not reconstructed eighteen months later from a shoebox of statements. The two edges of the contract carry the most risk, because that is where the part-year rules, the mismatched calendars and the day-counting tests all collide at once. For the arrival and departure years in particular, these are the documents and data points worth coordinating from the start:

Exact travel dates in and out of the UK and the US, with a running day count for both the Statutory Residence Test and the 330-day physical presence test
Your UK employment contract, assignment letter and payslips, showing start and end dates, salary, bonuses and any relocation or housing allowances
UK PAYE records and the P60 or P45, plus evidence of UK income tax actually paid, to support the Foreign Tax Credit
A split-year analysis identifying which UK case applies and the date on which the UK part of the year begins or ends
Opening dates and monthly high balances for every UK bank, savings and investment account, in sterling and converted to dollars, for the FBAR and any Form 8938
The certificate of coverage confirming which country's social security system applies for the duration of the posting
An apportionment schedule mapping each UK tax year onto the two US calendar years it straddles, with the exchange rates used recorded
Any US-source income, estimated-tax payments and prior-year carryovers that still belong on the Form 1040 while you are abroad

Handled as a single coordinated project, a US citizen on a UK fixed-term contract can move in and out of the country without ever paying tax twice on the same pound and without tripping an information-reporting penalty. Handled as two unrelated returns, the move years produce gaps, double charges and amendments. That is the whole argument for treating US UK tax returns preparation as one exercise spanning both systems, started early and documented as you go, so that the arrival and departure years are planned rather than repaired.