UK Self Assessment for Americans: How It Fits With Your US Return

UK Self Assessment for Americans means running two returns in parallel: an HMRC return on your UK tax year, and a Form 1040 on the US calendar year. Neither cancels the other. What stops you paying twice is relief claimed in the right direction, on the right pages, in the right order.

The mechanics of the UK return are covered in our guides to whether you need to file Self Assessment and getting a UTR number. This one is about the join: which parts of the UK return carry the cross-border work, how the two credit systems interact, and why the order you prepare them in changes the answer.

How does UK Self Assessment work for Americans?

UK Self Assessment works the same way for Americans as for anyone else who is UK resident. HMRC taxes on residence, and the Statutory Residence Test decides it. A UK resident is normally taxable on worldwide income, so US dividends, US rent and US self-employment income all belong on the UK return alongside UK salary.

What is different is that nothing you do on the UK return releases you from the US one. The IRS states that US citizens abroad are subject to tax on worldwide income from all sources. The same income is therefore reported twice, in two currencies, across two different year ends. The returns are separate filings, but they are not independent documents.

Which pages of the UK return carry the cross-border work

The main return is the SA100. Most of what matters for an American sits in the supplementary pages, which GOV.UK lists on its Self Assessment tax return forms page.

Page	What it covers	Why it matters to an American
SA100	The main tax return	Pulls the whole position together
SA106	Foreign income or gains	Where US income is reported and Foreign Tax Credit Relief is claimed
SA109	Non-UK residents or dual residents	Arrival and departure years, split-year claims, and treaty residence positions
SA105	UK property income	A UK rental, including finance cost restrictions
SA108	Capital gains	Share sales and property disposals on either side of the Atlantic
SA102	Employees or company directors	UK employment already taxed under PAYE
SA103S / SA103F	Self-employment, short or full	Consulting income, including work invoiced to US clients

SA106 and SA109 are the two that a single-country UK accountant may rarely see and that a cross-border return almost always needs. They are also the pages HMRC's free online service does not always support, which can force a non-resident return onto paper or commercial software.

Which country gives the credit, and how much?

Both systems relieve double taxation by crediting the other country's tax, and both cap the credit. The caps are what decide your final bill.

On the UK side

Foreign Tax Credit Relief is claimed on the SA106 pages. HMRC's HS263 helpsheet for 2025/26 puts the limit plainly: the relief "can only ever reduce the liability to UK tax on overseas income, it can never be more than the UK tax liability". If the US tax on a piece of income exceeds the UK tax on it, the excess is not refunded by HMRC. Where there is more than one source, HS263 says the claims are worked through one at a time, each later calculation excluding the income already dealt with.

On the US side

The IRS allows a credit for foreign taxes you paid or accrued, and says individuals claim it on Form 1116. The alternative is an itemised deduction, which is usually worth less because a credit reduces the US tax itself while a deduction only reduces taxable income. Because UK rates are often higher than US rates on the same income, many Americans in the UK end up with the US liability reduced to nil and unused credits left over.

Illustrative example: an American in London with UK employment income and a US brokerage account has UK tax on the dividends and US tax on the same dividends. The UK return reports the dividends on SA106 and claims Foreign Tax Credit Relief for the US tax, capped at the UK tax on that dividend income. The US return reports the same dividends and claims a foreign tax credit on Form 1116 for UK tax on UK-source income. Neither claim is made until the direction of relief for each income source has been settled, because claiming in both directions on the same income does not work.

Why the two tax years never line up

The UK tax year runs from 6 April to 5 April. The US tax year is the calendar year. A dividend paid in February 2026 falls in the UK year ended 5 April 2026 and in the US year ended 31 December 2026. Nothing reconciles that for you.

Three consequences follow. First, every figure has to be reallocated to the right year on each side rather than copied across. Second, foreign tax has to be matched to the income it relates to, not to the date the payment happened to leave your account, which is where the distinction between taxes paid and taxes accrued starts to matter on the US return. Third, currency conversion has to be consistent and documented, because the same income appears in sterling on one return and dollars on the other.

The deadlines compound it. The UK online return for the year ended 5 April 2026 is due by 31 January 2027, per HMRC's published deadlines, while the US return for calendar 2025 was due long before that, with extensions running to 15 June and 15 October 2026 for citizens abroad. The US return is often filed before the UK tax on overlapping income is finally known, which is precisely why the sequencing below matters.

In what order should you prepare the two returns?

1. Fix residence first. Settle UK residence under the Statutory Residence Test, and any split-year position, before any income is allocated. Everything else depends on it.
2. Sort each income source by where it arises. UK employment, UK property, US dividends, US rental and self-employment each have a country of source, and that drives which country taxes first.
3. Decide the direction of relief for each source. One country taxes first, and the other gives the credit. Getting this backwards on even one source can waste the relief entirely. Our guide to double taxation relief between the US and UK works through how the treaty and the two credit systems fit together.
4. Quantify the UK tax. Compute the UK liability, including Foreign Tax Credit Relief on SA106, so the US preparer has a real number rather than an estimate.
5. Complete the US return. Claim the foreign tax credit on Form 1116 using the UK figures, and extend the US return if the UK numbers are not ready in time.
6. Reconcile before filing either. Check that each income source appears once on each return, in the right year, with relief claimed in one direction only.

Payments on account: the UK bill nobody budgets for

A first UK tax bill often arrives with a second one attached. GOV.UK explains that payments on account are advance payments towards your next bill, due by midnight on 31 January and 31 July, and that each payment is half of the tax you owed last year.

Situation	Payments on account?
Last year's tax bill was less than £1,000	No
More than 80% of last year's tax was collected at source, for example through PAYE	No
Neither exception applies	Yes, on 31 January and 31 July

For an American whose UK salary is taxed under PAYE but whose US investment income is not, the 80% test is the one to watch. A year with a large US capital gain or a big dividend can tip the balance, turning one expected bill into a balancing payment plus half of it again on the same date.

What your US preparer needs from the UK return

• The UK tax computation, showing the tax on each income source rather than a single total.
• The SA106 figures, with foreign income and the foreign tax claimed against it.
• The residence position and any split-year dates from SA109.
• Dates and amounts of UK tax actually paid, including payments on account.
• The exchange rates used, and the basis on which they were chosen.

If your UK accountant and your US preparer never exchange these, each one is guessing at the other's numbers. That is the most common reason relief is lost in cross-border filings, and it is entirely avoidable.

Amending the UK return when the US numbers move

Cross-border returns get amended more often than domestic ones, because a figure on one side can change after the other side has been filed. An IRS adjustment, a late corrected 1099, or a revised allocation of foreign tax can all move the UK position after 31 January.

HMRC allows the return to be corrected, within a window. GOV.UK says that for the 2024 to 2025 tax year you will usually need to change your return by 31 January 2027, which is twelve months after that year's online filing deadline, and the same pattern applies to later years. An online amendment cannot be made in the first 72 hours after filing; after that, you sign in, select the tax year, make the corrections and file again. A paper amendment means sending the corrected SA100 pages marked "amendment" with your name and UTR.

After the twelve months have passed, GOV.UK says you have to write to HMRC instead. Where the change means you overpaid, a claim for overpayment relief can be made up to four years after the end of the tax year it relates to. That four-year window is worth knowing about, because Americans who discover that relief was claimed in the wrong direction in an earlier year are often outside the ordinary amendment period by the time they find out.

What people get wrong

Treating the UK return as the whole job

A UK return reports income to HMRC. It does nothing about US information reporting, which has its own thresholds and penalties and runs on the US calendar year.

Claiming relief in both directions

Each income source gets relieved once, in one country. Claiming a credit on both returns for the same tax invites an enquiry on at least one side.

Filing the US return on estimates and never amending

When the US return is filed before the UK liability is final, the estimate needs revisiting once the UK figure is known. Extensions exist for this reason.

Forgetting the UK bill is not just the tax

Payments on account can nearly double the amount leaving your account on 31 January in a first full year.

Getting both returns to agree

US/UK Cross Border Tax is US CPAs and UK tax advisers working as one team, with offices in London, Manchester, New York and San Francisco. Both returns are prepared by people who can see both, which is what lets residence dates, income allocation and foreign tax credits line up rather than be reconciled after the fact.

If you want UK Self Assessment handled with your US return in view, see our UK Self Assessment service, read how we work with Americans living in the UK, or get in touch with your income sources and we will set out what each return needs and in what order.