UK Self Assessment
SA100, SA109, Treaty, US v UK
Self Assessment returns for UK residents with US income, residence questions or treaty claims, prepared with the US return in view.
What does UK Self Assessment involve?
The UK tax year runs from 6 April to 5 April, and Self Assessment is how HMRC collects tax on anything PAYE does not reach. For people with US connections that usually means US dividends, US rent, US pensions, or a residence position that needs stating. We prepare the SA100 and its supplementary pages alongside the US return.
Forms and filings involved
- SA100
The main UK Self Assessment return, with supplementary pages for foreign income, property, gains and residence.
- SA109
The Self Assessment pages for residence status, split-year treatment, treaty residence claims and foreign income and gains claims.
- Treaty
How the US-UK income tax treaty allocates taxing rights, and where its saving clause limits what US citizens can claim.
- US v UK
The structural differences between the US and UK income tax systems that cause most cross-border problems, from tax years to ISAs.
Self Assessment when part of your life is American
Anyone who needs to file for the first time must register by 5 October following the end of the tax year.
Paper returns are due by 31 October and online returns by 31 January, which is also the date for the balancing payment and the first payment on account. The second payment on account falls on 31 July. US filers should note the order of events: UK tax for a year is often still unpaid when the US return covering the same months is due, which affects the timing of foreign tax credits.
Foreign income and foreign tax credit relief go on the SA106 pages. Residence, split-year treatment and treaty claims go on SA109. HMRC's own free online service does not support SA109, so a return that includes it must be filed through commercial software or on paper. Residence itself is decided by the Statutory Residence Test, which looks at days, ties, work and accommodation together. It is a different test from the US substantial presence test, and the two can give different answers for the same person.
The remittance basis was abolished from 6 April 2025. In its place, people who become UK resident after ten tax years of non-residence can claim relief on foreign income and gains for their first four tax years. The claim is made on the return, and claiming it costs the personal allowance and the capital gains annual exempt amount for that year. For a US citizen the relief is worth less than it appears: the US still taxes the same income, and with no UK tax paid there is no credit to set against it.
What the UK return includes
- 01
- SA100 with SA106 foreign pages and SA109 residence pages where needed
- 02
- Statutory Residence Test analysis, including split-year treatment
- 03
- Foreign tax credit relief for US tax on US-source income
- 04
- Claims under the foreign income and gains regime for new arrivals
- 05
- Payments on account calculated and, where the facts justify it, reduced
Who this is for
Americans in the UK with US investment, rental or pension income
- Directors, landlords and the self-employed who also file in the US
- New arrivals from the US in their first UK tax years
- British nationals leaving for the US who need a split-year return
Why US UK Tax Returns
Each return is prepared with the other country's return open beside it, so a credit, election or disclosure on one is supported by the other.
One File
US and UK returns prepared in the same engagement and reconciled line by line.
Primary Sources
Every position traced to the Code, the treaty, IRS instructions or HMRC guidance.
Scope First
Returns, forms, years and fee agreed in writing before work begins.
The Same People
The team that files this year carries the elections and credits into the next.
Questions we are asked
Why can't I file my return through HMRC's own website?
You can, unless the return needs the SA109 residence pages. HMRC's free online service does not support SA109, which is where non-residence, split-year treatment and treaty claims are made. A return that includes it has to go through commercial software or on paper, and the paper deadline is earlier than the online one. Many people with US connections need SA109 in the year they arrive or leave, and some need it every year.
Does HMRC give me credit for tax I have paid to the IRS?
Generally only for US tax the treaty allows the US to charge as the source country, and never more than the UK tax on the same income. On US portfolio dividends, for example, that is generally 15%. Extra US tax charged only because you are a US citizen is not creditable in the UK. The treaty deals with that layer on the US return instead, so the two returns have to be prepared together.
I moved to the UK partway through the year. Am I taxed on the whole year?
Under the Statutory Residence Test a person is resident or non-resident for a whole tax year. Split-year treatment is a separate relief that divides the year into a UK part and an overseas part, but only where one of its specific cases applies. It is claimed on SA109. Whether a case applies depends on work, home and arrival facts, so the dates need checking before the relief is assumed.
Primary sources
What this page says is drawn from the official material below. Read it yourself; we would rather be checked than trusted.
Last reviewed
From the Blog
Ready to talk it through?
Tell us where you live, what you hold and which years are outstanding. We will say what applies and what it involves before any work begins.
Contact us