SA100
HMRC, UK Self Assessment Tax Return
The main UK Self Assessment return, with supplementary pages for foreign income, property, gains and residence.
What is SA100?
The SA100 is the core of a UK Self Assessment return. It covers UK income that PAYE does not reach and gathers the supplementary pages that carry foreign income, property, gains and residence claims. For people with a US connection it is usually the place where US income meets UK tax.
How the UK return is put together
The SA100 records employment income already taxed under PAYE, interest, dividends, pension income and reliefs such as pension contributions and Gift Aid.
Supplementary pages then carry the specialist items: SA106 for foreign income and foreign tax credit relief, SA105 for UK property, SA108 for capital gains, SA103 for self-employment and SA109 for residence and related claims. A US citizen resident in the UK often needs several of these each year.
The UK tax year runs from 6 April to 5 April. First-time filers must register by 5 October after the year ends. 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 for the following year. The second payment on account falls on 31 July. Late filing and late payment each bring their own penalties and interest.
US income goes on the return in sterling. US dividends, interest and rent are reported with any US tax withheld, and the treaty often limits which country has the first right to tax. Relief for US tax is claimed on SA106 and is capped at the UK tax on the same income. Where the US also taxes the same income because of citizenship, the US return usually gives the credit instead, so the two returns need to agree.
At a glance
- 5 October after the tax year ends
- Register by
- 31 January, with the balancing payment
- Online deadline
- 31 October
- Paper deadline
- HMRC, online or on paper
- Filed with
Figures are for the tax year stated in the official instructions linked below.
How we handle it
- UK Self Assessment
Self Assessment returns for UK residents with US income, residence questions or treaty claims, prepared with the US return in view.
- Cross-Border Tax
US and UK returns prepared together from one set of workpapers, so credits, tax years and exchange rates line up across both.
- Treaty Relief
Claims under the US/UK income tax treaty, with Form 8833 disclosure, residence tie-breaker analysis and reduced withholding on US income.
- Individual Tax Returns
US federal returns for Americans living in the UK and British nationals with US income, prepared with the UK figures in view.
Where people go wrong
The SA100 errors we correct most often.
Who files it
- UK residents with US dividends, interest, rent or pensions
- Self-employed people and partners in UK partnerships
- People with capital gains above the annual exempt amount
- Arrivals and leavers making residence or split-year claims
01
Leaving US accounts off because the IRS already taxes them
02
Claiming UK credit for US tax that the treaty says the US cannot keep
03
Missing payments on account after the first year of higher tax
04
Filing without SA109 when residence or treaty claims are needed
Why US UK Tax Returns
Every form is prepared against the official instructions, and every position on it is one we can point to in the Code, the treaty or HMRC's guidance.
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
I pay all my UK tax through PAYE. Why would I need to file an SA100?
PAYE deals with salary and some benefits, but it does not reach most foreign income. US dividends, interest, rent or gains usually need reporting through Self Assessment, as can a residence claim in your year of arrival. HMRC's online checker gives a first answer, and the position depends on your income and circumstances in the particular year.
I am a US citizen living in the UK. Which country gets the first bite of my US dividends?
Under the treaty the US generally keeps withholding on US dividends at a reduced rate, and the UK taxes the dividend while giving credit for that withholding. The US may then tax the same dividend again because you are a citizen, and relief for that further layer usually comes through the US return. The ordering depends on the type of income, so each stream needs checking.
Can I file my SA100 through HMRC's own online service?
For many people, yes. The limitation is SA109. If you need to make a residence, split-year or treaty claim, those pages cannot be filed through HMRC's free online service, and the return has to be filed with commercial software or on paper. Paper returns have an earlier deadline, which is worth knowing before choosing that route.
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
Also in UK Forms
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Need SA100 prepared or reviewed?
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.
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