The UK side: residence, split year and the FIG window
UK residence has nothing to do with your visa; it is decided mechanically by the Statutory Residence Test across the tax year running 6 April to 5 April. Arrive mid-year and split-year treatment usually divides the year so you are taxed as a resident only from arrival, though your calendar-year Form 1040 keeps running underneath. Most Americans qualify for the FIG regime because anyone who has never been UK resident meets the 10-year non-residence test automatically: a claim on the SA109 pages gives full UK relief on qualifying foreign income and gains for up to four years, at the cost of the £12,570 personal allowance and the CGT annual exempt amount each claim year. Arrival timing matters: a split year still burns a full year of the four-year clock, so landing shortly after 6 April usually works best.
The US side does not switch off
The United States taxes on citizenship, not residence, so citizens and green card holders keep filing worldwide-income returns from the UK, and FBAR and FATCA reporting picks up new UK accounts once thresholds are met. On the US return, the Foreign Earned Income Exclusion shelters up to $132,900 of foreign earned income for 2026, but for most Americans employed in the UK the foreign tax credit works out better because UK rates are generally higher, and the FEIE election stays in effect until revoked. The critical interaction: income sheltered by a FIG claim carries no UK tax to credit, so the US tax on it stands, which makes every FIG claim a two-country calculation. Watch the account traps too: UK funds and ISA holdings are generally PFICs for US purposes, with punitive treatment, so review structures before you open anything.
Two calendars, one sequence
You will run two filing clocks: UK Self Assessment online by 31 January after the 5 April year end, with the SA109 needing commercial software or an adviser, and the US return due 15 April with an automatic extension to 15 June for Americans abroad. The rhythm that works is UK first, US second, so the UK figures feed the foreign tax credit workings on the calendar-year US return; the US-UK treaty then stops the same income being fully taxed twice. Horizon UK Tax Solutions runs the UK side on fixed fees agreed upfront, with expat returns from £550 and complex cross-border cases from £750, while US filings are handled by our US partners (Enrolled Agents and CPAs), whom we coordinate for you; book a free clarity call at /book to plan the move before the SRT clock starts.