UK Tax Essentials for US Citizens Living in the UK

Two tax systems, one taxpayer

The United States taxes its citizens on worldwide income wherever they live. The UK taxes people based on residence. Live in the UK as an American and you sit squarely inside both systems at once: HMRC because you are here, the IRS because of your passport.

That does not usually mean paying tax twice on the same pound. The US–UK treaty, foreign tax credits and various exclusions exist to prevent it. But relief is claimed, not automatic — and the two systems disagree often enough (on tax years, on what counts as income, on which wrapper is tax-favoured) that unmanaged filing routinely leaks money.

UK residence: when HMRC's claim begins

Your UK position turns on the Statutory Residence Test, a mechanical set of rules based on days in the UK and connections to it. Arrive part-way through a tax year and split-year treatment may divide the year into a non-resident part and a resident part. The full mechanics are covered in our residence and FIG guide; the headline is that residence is determined by the rules, not by intention, visa status or where you feel at home.

Once resident, the default is that the UK taxes your worldwide income and gains — the US salary trailing off, the brokerage dividends, the rental income from the house you kept. All of it is in scope unless a specific relief says otherwise.

The FIG regime: a four-year window for new arrivals

From 6 April 2025, the UK abolished the remittance basis and replaced it with a regime for foreign income and gains (FIG). Broadly, someone who becomes UK resident after a sufficiently long period of non-residence (ten years) can claim relief from UK tax on qualifying foreign income and gains for up to their first four years of residence — even if the money is brought to the UK, which the old remittance basis punished.

For an American, the catch is immediate: income the UK relieves does not vanish. It is still fully taxable on your US return, now with less UK tax available as a credit against it. Whether a FIG claim actually saves anything is a two-country calculation, different for every mix of income — one of the clearest examples of why UK choices cannot be made in a UK-only vacuum.

PAYE, Self Assessment, or both

Most UK employees are taxed through PAYE: tax and National Insurance come out of salary automatically, and many people never file anything. Americans in the UK are rarely that lucky. US-source income, investment income, self-employment, rental income, or a claim to split-year or FIG treatment will generally pull you into Self Assessment — registration by 5 October after the relevant tax year, online filing by 31 January.

Meanwhile the US return continues every year regardless, on the calendar year, with expat deadlines of its own (an automatic extension to 15 June for those abroad, and 15 October on request). Two returns, two year-ends, one set of income. Sequencing them properly is half the job.

The US shadow over every UK choice

This is the theme that runs through everything an American in the UK does financially. UK-sensible moves can be US-toxic, and vice versa:

None of these are reasons to avoid UK life — they are reasons to check the US angle before committing, when the choice is still free.

Getting the setup right

The pattern we see most is not exotic avoidance gone wrong; it is ordinary life — an ISA opened on a bank's suggestion, a UK fund bought in a brokerage account, a bonus deferred into the wrong year — creating US problems nobody flagged. A single review of your income, accounts and plans against both systems, ideally in your first year of residence, prevents most of it. That is the work we do, on fixed fees, with both returns prepared under one roof.