A UK Self Assessment late filing penalty starts at £100 the day after the 31 January online deadline, even if you owe no tax. After three months HMRC adds £10 a day for up to 90 days, then 5% of the tax due or £300 at six and twelve months. Late payment adds separate 5% penalties and interest. US citizens in the UK are frequent targets.
Americans in Britain juggle two calendars. The IRS wants Form 1040 by 15 April, or 15 June if you live abroad, while HMRC wants the Self Assessment return by 31 January. Many US citizens put all their energy into the IRS deadline and miss the UK one, often because they assumed PAYE had settled everything. This guide sets out the HMRC penalty timeline for the 2025-26 return, how interest works, how to appeal, and why UK penalties do nothing for your US foreign tax credit.
How the UK Self Assessment late filing penalty works
HMRC charges penalties for late returns and, separately, for late payment. The late filing penalties apply because the return is late, not because tax is unpaid. Consequently, a US citizen with only PAYE salary who receives a notice to file still faces the £100 penalty if the return arrives late.
The deadlines for the 2025-26 tax year
The 2025-26 UK tax year ran from 6 April 2025 to 5 April 2026. If you need to file and have not registered, you must tell HMRC by 5 October 2026. The paper return is due by 31 October 2026 and the online return by 31 January 2027. Any balance of tax, plus the first payment on account for 2026-27, is also due on 31 January 2027.
The penalty timeline
The GOV.UK Self Assessment penalties guidance sets out fixed and tax-geared penalties. The table below applies them to a 2025-26 online return.
| How late (2025-26 online return) | Date reached | Late filing penalty (GOV.UK) |
|---|---|---|
| 1 day | 1 February 2027 | £100 fixed penalty |
| 3 months | 1 May 2027 | £10 per day, up to 90 days (maximum £900) |
| 6 months | 1 August 2027 | Further 5% of the tax due or £300, whichever is greater |
| 12 months | 1 February 2028 | Another 5% of the tax due or £300, whichever is greater |
A return that is a full year late therefore costs at least £1,600 in filing penalties, even where no tax is due. In serious cases HMRC can charge up to 100% of the tax due at the 12-month point if it believes information was withheld deliberately.
Late payment penalties and interest
Late payment is a separate charge. Under the current Self Assessment rules, HMRC adds 5% of the unpaid tax at 30 days, six months and twelve months after the payment due date. Therefore, a £10,000 bill left unpaid for a year attracts £1,500 in late payment penalties before interest.
How HMRC interest is calculated
HMRC also charges late payment interest from the due date until you pay. Since 6 April 2025 the rate has been the Bank of England base rate plus 4 percentage points. HMRC lists the rate as 7.75% from 9 January 2026 on its HMRC interest rates page, and it moves whenever the base rate changes. Notably, interest runs on penalties too if you do not pay them within 30 days of the penalty notice.
Making Tax Digital penalties from April 2026
Sole traders and landlords with qualifying income above £50,000 joined Making Tax Digital for Income Tax from 6 April 2026. For them, a points-based regime for late submissions and a revised late payment regime replace the older rules. HMRC has said it will not issue penalty points for late quarterly updates in 2026-27, although the updates remain compulsory. Our guide to Making Tax Digital for Income Tax explains who is in scope.
Why US citizens in the UK miss the deadline
In our experience, US citizens rarely ignore HMRC. Instead, they misjudge whether they need to file at all.
Common triggers
You generally need a Self Assessment return if you are self-employed, receive untaxed income such as rental or foreign income, or owe the High Income Child Benefit Charge. Additionally, US citizens often have US-source dividends, a US brokerage account or interest from a US bank, all of which count as foreign income for a UK resident. Similarly, anyone who used the new foreign income and gains regime must claim it on a return.
The two-calendar problem
UK tax is due on 31 January, but the US foreign tax credit is claimed on the US return for the same calendar year. Specifically, a UK tax bill for 2025-26 spans two US tax years, 2025 and 2026. If the UK figures are not final, your US preparer may estimate them, and a late or changed UK return can force an amended Form 1040. Our article on payments on account for US citizens in the UK explains how HMRC instalments interact with the IRS.
UK penalties and your US tax return
A common question is whether UK penalties count towards the US foreign tax credit. They do not. Treasury Regulation section 1.901-2 excludes penalties, fines and interest from the definition of a creditable foreign tax. As a result, only the underlying UK income tax enters Form 1116, which is explained on our foreign tax credit and double taxation page.
| HMRC charge | Creditable on Form 1116? | Deductible on Form 1040? |
|---|---|---|
| UK income tax | Yes, subject to the section 904 limitation | Only if you itemise instead of claiming the credit |
| Late filing penalty | No | No |
| Late payment penalty | No | No |
| Late payment interest | No | Generally no, as personal interest |
Furthermore, late UK payment can delay the year in which you claim the credit if you use the cash method, so the penalty costs you twice.
How to appeal a Self Assessment penalty
You can appeal if you had a reasonable excuse. HMRC accepts events such as serious illness, the death of a close relative or an HMRC system failure. However, relying on someone else, finding the return difficult or not receiving a reminder are not reasonable excuses on their own.
Time limits and method
You must normally appeal within 30 days of the penalty notice, online or with form SA370. You must also file the late return or pay the tax promptly once the excuse ends. If you never needed to file, ask HMRC to withdraw the notice to file instead, because that can cancel the penalty.
A worked example
Consider an illustrative client, an American engineer in Edinburgh with a UK salary and a US brokerage account. He filed his 2024-25 return in September 2025, seven months late, with £2,400 of tax due on US dividends. His penalties were £100, plus £900 in daily penalties, plus £300 at six months, because 5% of £2,400 is only £120. He also paid late payment penalties and interest on the £2,400. None of those charges reduced his US tax, so filing on time would have saved him at least £1,300.
How Tranzesta can help
We prepare UK Self Assessment and US Form 1040 returns together, so both calendars line up and the foreign tax credit uses final UK figures. We also review penalty notices, draft reasonable excuse appeals and ask HMRC to withdraw notices that should never have been issued.
If you are a US citizen in the UK and unsure whether you need to file by 31 January 2027, book a consultation with Tranzesta. We will confirm your obligations before HMRC's penalties start running.
Frequently Asked Questions
What is the UK Self Assessment late filing penalty?
The UK Self Assessment late filing penalty is £100 for a return filed even one day late. After three months HMRC adds £10 a day for up to 90 days. At six months and again at twelve months it adds 5% of the tax due or £300, whichever is greater, according to GOV.UK.
Do I pay a Self Assessment penalty if I owe no tax?
Yes, HMRC charges the £100 late filing penalty and the daily penalties even if you owe no tax or have already paid it. The penalty is for the late return itself. If you were never required to file, you can ask HMRC to withdraw the notice to file, which can cancel the penalty.
When is the 2025-26 Self Assessment return due?
The 2025-26 Self Assessment return is due by 31 October 2026 on paper or 31 January 2027 online. Any balancing payment for 2025-26 and the first payment on account for 2026-27 are also due on 31 January 2027. New filers must register with HMRC by 5 October 2026.
Can a UK late filing penalty be claimed as a US foreign tax credit?
No, a UK late filing penalty cannot be claimed as a US foreign tax credit. Treasury Regulation section 1.901-2 excludes penalties, fines and interest from creditable foreign taxes. Only the underlying UK income tax goes on Form 1116, subject to the section 904 limitation.
What counts as a reasonable excuse for HMRC?
HMRC accepts a reasonable excuse where an unexpected event beyond your control stopped you filing, such as serious illness, the death of a close relative or an HMRC online service failure. Relying on an accountant, finding the return hard or not receiving a reminder are not usually accepted on their own.
Do US citizens in the UK have to file Self Assessment?
Not all US citizens in the UK must file Self Assessment. A return is usually needed for self-employment, rental income, untaxed foreign income such as US dividends or interest, or a High Income Child Benefit Charge to pay. A US citizen with only PAYE salary and no other income often does not need one unless HMRC issues a notice to file.
Does the UAE charge late filing penalties on personal tax returns?
No, the UAE does not charge late filing penalties on personal income tax returns, because it has no personal income tax on salary. A person running a UAE business, however, can face Federal Tax Authority penalties for late corporate tax or VAT registration and filing.
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