The Arrival-Year Playbook: Your First US to UK Tax Year

The UK taxes by reference to a year running 6 April to 5 April; the US taxes individuals on the calendar year. A mid-year mover therefore straddles the UK's 2026/27 year and the US 2026 year, and each country applies its own residence rules to its own year. The IRS position is blunt: US citizens and resident aliens abroad remain subject to US tax on worldwide income and must keep filing (IRS guidance). Moving to the UK never switches the US side off; it adds a UK layer on top.

The practical consequence is sequencing. Your first full US return as a UK resident (the 2026 return, filed in 2027) lands months before your first UK Self Assessment return (the 2026/27 return, due by 31 January 2028). Decisions made on the US return, particularly the exclusion-versus-credit choice covered below, interact with what you later claim on the UK return, so the two preparers need to be working from the same plan rather than meeting each other's numbers after the fact.

UK residence for 2026/27 is decided by the Statutory Residence Test (SRT), and the answer is all-or-nothing for the year. Most arrivers become resident through one of the automatic UK tests: spending 183 or more days in the UK in the year, having their only home in the UK for a qualifying period, or working full-time in the UK. If no automatic test bites, the sufficient-ties test counts your UK connections (family, accommodation, work, past UK days) against a sliding day-count scale.

Taken alone, that would make a September 2026 arriver UK resident for the whole of 2026/27, exposing their US income and gains arising between 6 April 2026 and the arrival date to UK tax (anything earlier falls in 2025/26, when they were still non-resident). Split-year treatment is what prevents that outcome, which is why it is the single most valuable relief in the arrival year. You can model your dates with our split-year tool before anything is filed.

The SRT contains eight split-year cases (HMRC manual RFIG21000): three for people leaving the UK and five for people arriving. All the arriver cases require you to have been non-UK resident in the previous tax year, which a genuine US-to-UK mover will almost always satisfy. The five cases relevant to arrivers are:

• Case 4: you start to have your only home in the UK during the year and keep it to 5 April.
• Case 5: you start full-time work in the UK, meeting the sufficient-hours test over 365 days.
• Case 6: you return to the UK after a period of qualifying full-time work overseas.
• Case 7: you accompany a spouse or partner who qualifies under Case 6.
• Case 8: you start to have a home in the UK during the year and keep it for the rest of the year and the whole of the following tax year.

Where the year splits, the overseas part comes first: your US salary, dividends and gains arising before the split date are broadly outside UK tax, and only income and gains from the split date onwards fall fully within the UK net. If more than one case fits, statutory priority rules fix the case and the date; Cases 6 and 7 broadly take priority, and otherwise the case producing the earliest split date wins, so you do not get to choose the most favourable date. Split-year treatment is claimed on the SA109 residence pages of your return; it is not applied automatically.

Most arrivers from the US also qualify for the four-year Foreign Income and Gains (FIG) regime, provided they were non-UK resident for the 10 tax years immediately before arrival (GOV.UK guidance). A valid claim relieves qualifying foreign income and gains from UK tax for up to your first four UK-resident years, with no charge for bringing the money into the UK. Check your dates with our FIG checker, and note that a split arrival year still burns one of the four years even if you were only UK resident for a few months of it.

The claim lives on the same SA109 pages as your split-year claim: box 28 for foreign income, box 29 for foreign gains, with every relieved amount reported source by source on the supplementary pages. Our SA109 walkthrough covers the mechanics. Two costs matter. Claiming for a year forfeits your £12,570 Personal Allowance and £3,000 capital gains exempt amount for that year, so small claims can lose money. And for a US citizen there is a second-order effect: FIG relief takes the UK tax on that income to nil, which means there is no UK tax to credit on your US return, so the income is simply taxed in the US instead. Whether a FIG claim actually saves the household anything is a two-country calculation, not a UK one.

Your first UK deadlines for a 2026/27 arrival: register for Self Assessment by 5 October 2027 if HMRC has not already issued a return, file on paper by 31 October 2027, or file online and pay by 31 January 2028. HMRC's free online service does not support the SA109, so in practice you need commercial software or an agent. We prepare year-of-arrival returns, SA109 and all, on fixed fees from £550.

The US side of the arrival year is prepared by US-qualified professionals, but it helps to know the shape of it. Your 2026 Form 1040 covers the whole calendar year, including your post-move UK income. The regular due date is 15 April 2027, with an automatic extension to 15 June for taxpayers living abroad and a further extension to 15 October via Form 4868; the FBAR for foreign accounts is due 15 April through the BSA e-filing system, with an automatic extension to 15 October that does not need to be requested.

Once you are UK resident, double tax on your earnings is managed through one of two US mechanisms. The foreign earned income exclusion (Form 2555) can exclude up to $132,900 of foreign earnings for 2026 (IRS inflation adjustments), but only once you meet the bona fide residence test or the 330-day physical presence test, which a mid-year mover often cannot satisfy by the normal filing deadline; many extend until they qualify. The alternative is the foreign tax credit (Form 1116), which credits UK tax paid against the US liability and often suits people whose UK tax rate exceeds their US rate, since the UK tax can cover the US bill in full. The choice is sticky (revoking the exclusion has a five-year consequence), so it is a decision your US preparer models rather than a box ticked by default.

Two further US issues deserve early attention. Green card holders remain US resident aliens, taxed on worldwide income, until their status is abandoned or a treaty election changes the position; abandoning mid-year creates a dual-status year with real restrictions (no standard deduction and, generally, no joint filing) (IRS dual-status rules), and for long-term green card holders a treaty non-residence election can trigger expatriation consequences, so it needs specific US advice first. Separately, state residency is its own exit: some states apply domicile-based tests and can continue to assert residency after you leave the country, so documenting a clean break with your former state (and establishing that you have made your home elsewhere) is part of the move, not an afterthought.

During the overlap months you may be resident in both countries under their domestic rules at the same time. The US-UK Double Taxation Convention (GOV.UK) resolves this through the Article 4 tie-breaker, a cascade you stop at the first decisive step: permanent home, then centre of vital interests, then habitual abode, then nationality, then mutual agreement between the two authorities. For most arrivers the tie-breaker points to the UK from around the date the UK home and life are established.

For US citizens the tie-breaker has a hard limit: the saving clause in Article 1 lets the US tax its citizens as if the treaty did not exist. Winning the tie-breaker does not stop the IRS taxing you; it mainly shapes which country taxes first and which gives credit, with Article 24 (including its re-sourcing rule) making the credits work. A treaty position taken against US domestic law is disclosed on Form 8833. The overlap period is where UK and US filings most often contradict each other, and where having both sides coordinated pays for itself.

The timeline below shows how the pieces land for an illustrative September 2026 move from the US to the UK. It is a planning skeleton, not advice: your split date, case and deadlines depend on your own facts.

One habit makes the whole year easier: keep a single dated record of flights, home moves, employment start dates and account balances from the start. The same evidence supports your SRT day counts, your split-year case, your FIG disclosure and your US residence tests, and it is far easier to capture in the month it happens than to reconstruct eighteen months later. Many people also review how their US accounts and funds will be treated under UK rules with their adviser before the move, since the UK taxes some US fund structures unfavourably once you are resident.