A US citizen living in Britain files UK Self Assessment on UK income and, if UK resident, on worldwide income — while still filing a US Form 1040. UK residence is decided by the Statutory Residence Test. The trap is that British reliefs (ISAs, salary sacrifice, Gift Aid, BADR) reduce UK tax without US recognition, shrinking the foreign tax credit that shelters your US bill.
The British half is usually the more straightforward of the two. Self Assessment is filed online by 31 January following the end of the tax year on 5 April, with payments on account in January and July.
The complication is that decisions taken for good British reasons have unadvertised American consequences — and the person advising on the British side generally has no reason to raise them.
The SRT works in three stages. The automatic overseas tests can make you non-resident outright. The automatic UK tests can make you resident outright. If neither settles it, the sufficient ties test combines days in the UK with connecting factors — family, accommodation, work, 90-day and country ties — to produce an answer.
Split-year treatment can divide a tax year into resident and non-resident parts in defined circumstances, but it applies only in specific cases and it is claimed rather than automatic.
US citizenship makes none of this go away. You can be conclusively non-resident in Britain and still owe a full US return on the same income.
| Item | 2026-27 |
|---|---|
| Tax year | 6 April to 5 April |
| Online Self Assessment deadline | 31 January following the year end |
| Personal Allowance | £12,570, tapered above £100,000, nil at £125,140 |
| Basic / higher / additional rate | 20% / 40% / 45% |
| Dividend ordinary / upper rate | 10.75% / 35.75% (raised from April 2026) |
| Capital gains, shares | 18% within the basic band, 24% above |
| CGT annual exempt amount | £3,000 |
From 6 April 2025 the remittance basis was replaced by the four-year foreign income and gains regime. Someone who has not been UK resident in the previous ten years can claim exemption on foreign income and gains for their first four years of residence.
For an American the benefit is double-edged. FIG removes the UK charge — and with it the UK tax that would have generated a foreign tax credit. You can end up paying full US tax on income Britain has chosen not to tax at all, which is a worse outcome than paying UK tax and crediting it.
Domicile was replaced for IHT purposes from 6 April 2025 by a long-term residence test: broadly ten of the previous twenty tax years of UK residence brings worldwide assets into the UK net, with a tail of three to ten years after departure.
The US–UK estate tax treaty dates from 1978 and was written around domicile, not a residence day-count. It has not been renegotiated to match, so a long-term resident American can face both systems asserting a primary claim over the same assets with a treaty that does not cleanly resolve it.
Yes, on the same basis as anyone else — UK residents are taxable on worldwide income, non-residents on UK-source income. US citizenship changes nothing about the British obligation. It adds a second, parallel obligation to file a US return on the same income, relieved through the foreign tax credit rather than by exemption.
By the Statutory Residence Test, applied in three stages: automatic overseas tests, then automatic UK tests, then the sufficient ties test combining days in the UK with family, accommodation, work, 90-day and country ties. Split-year treatment can divide a year of arrival or departure, but only in defined circumstances and it must be claimed.
Usually not, and often actively harmful. The wrapper means nothing to the IRS, so income and gains are taxable on your Form 1040 as they arise, and a stocks and shares ISA holding UK funds is normally a portfolio of passive foreign investment companies taxed under the punitive section 1291 regime with Form 8621 reporting for each holding.
The four-year foreign income and gains regime replaced the remittance basis from 6 April 2025, exempting foreign income and gains for the first four years of UK residence after ten years away. For a US citizen it can backfire: exempting the income in Britain removes the UK tax that would otherwise have generated a foreign tax credit, leaving full US tax with nothing to offset it.
31 January following the end of the tax year for online filing — so the 2026-27 year, ending 5 April 2027, is due by 31 January 2028. Payments on account fall due on 31 January and 31 July. Paper returns have an earlier deadline of 31 October.
Sometimes, but it needs modelling rather than assuming. A sacrifice can be fully effective for UK income tax and National Insurance while producing no US deduction, which leaves you with US tax on income Britain has sheltered and a smaller foreign tax credit because less UK tax was paid. The answer depends on your credit position, not on the UK saving alone.
Before you sacrifice salary, open an ISA or claim a relief, let us model what it does to the other return.
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