Self Assessment Deadline 31 January 2027: A Timeline for Dual Filers

The Self Assessment deadline in 2027 is 11:59pm on 31 January 2027: by then HMRC must have your online return for the 2025 to 2026 tax year and the tax you owe for it. The date falls on a Sunday, so some payment methods have to be used by Friday 29 January. For Americans who also file in the US, this UK date sits between two US deadlines and affects the foreign tax credit on both the 2026 and 2027 US returns.

This guide sets out every date from now to October 2027 that matters to someone with a UK return and a US return: what is due, what can still be changed and what happens if a date is missed. Every UK date below is for the 2025 to 2026 tax year, which ran from 6 April 2025 to 5 April 2026. Every US date is for the 2026 calendar tax year.

What is due on the Self Assessment deadline of 31 January 2027?

Two things are due by 11:59pm on 31 January 2027: the online return for 2025 to 2026 and the tax owed for that year. GOV.UK's Self Assessment deadlines page sets out the full list for the year:

Date	What is due (2025 to 2026 tax year)
5 October 2026	Register for Self Assessment if you have not filed before (passed)
11:59pm, 31 October 2026	Paper return must be received by HMRC
11:59pm, 30 December 2026	Online return, if you want a bill under £3,000 collected through your PAYE tax code
11:59pm, 31 January 2027	Online return; balancing payment for 2025 to 2026; first payment on account for 2026 to 2027
31 July 2027	Second payment on account for 2026 to 2027

If you registered after 5 October 2026, GOV.UK says HMRC's letter or email will give you a filing deadline three months from its date. The tax is still due on 31 January 2027, so in that case the payment can fall due before the return.

The Sunday problem

31 January 2027 is a Sunday. You can still file online that day. Payments are different: GOV.UK's guidance on paying your Self Assessment bill says that when the deadline falls on a weekend or bank holiday, the payment must reach HMRC by the last working day before it, unless you pay by Faster Payments or by card. A Bacs transfer takes three working days and a first Direct Debit five. In practice, anyone not paying by Faster Payments or card should treat Friday 29 January 2027 as the real payment date, and earlier if the money is coming from a US account.

How much do you pay on 31 January 2027?

The 31 January 2027 payment is usually the balancing payment for 2025 to 2026 plus the first payment on account for 2026 to 2027. GOV.UK explains payments on account as advance payments, each normally half of the previous year's bill, due on 31 January and 31 July. The balancing payment is the year's total bill minus the payments on account already made.

You do not have to make payments on account if your bill for the previous year was less than £1,000, or if you paid more than 80% of your tax at source, for example through your tax code. Many employed Americans in the UK fall into the second group. The ones who do not are usually landlords, the self-employed, and people with large investment income or gains.

If you expect 2026 to 2027 income to be lower, you can ask HMRC to reduce your payments on account online or on form SA303. If you reduce them too far, HMRC charges interest on the shortfall. Our guide to HMRC payments on account explains how the figures are worked out.

Illustrative example: an American in Manchester owed £8,000 for 2024 to 2025 and paid two payments on account of £4,000 each for 2025 to 2026, on 31 January and 31 July 2026. Her 2025 to 2026 bill comes to £10,000. On 31 January 2027 she owes a balancing payment of £2,000 (£10,000 minus £8,000) plus a first payment on account for 2026 to 2027 of £5,000, half of £10,000: £7,000 in total. A second £5,000 follows on 31 July 2027. This example is illustrative and does not describe a real client.

The dual filer's timeline, October 2026 to October 2027

For an American living in the UK, the UK and US years overlap rather than line up. The UK return being finished now covers 6 April 2025 to 5 April 2026, while the US return being prepared next spring covers calendar 2026. Our article on the UK tax year versus the US tax year explains the mismatch. Here is how the dates fall in sequence:

1. Now to 31 October 2026. Paper filers only: HMRC must receive a paper return by 11:59pm on 31 October 2026, which is a Saturday. If you will miss it and can file online, file online by January instead. Our guide to the 31 October paper deadline covers who is affected.
2. 30 December 2026. Last date to file online and have a bill under £3,000 collected through your tax code, if you pay tax through PAYE. GOV.UK lists the conditions; the tax is then collected over 12 months.
3. Friday 29 January 2027. Last working day before the deadline. Pay by now unless you are using Faster Payments or a card.
4. 31 January 2027. UK online return for 2025 to 2026 filed, balancing payment and first 2026 to 2027 payment on account paid.
5. 15 April 2027. US Form 1040 for 2026 due, and the date from which the IRS charges interest on unpaid US tax. The FBAR for 2026 is also due, with an automatic extension.
6. 15 June 2027. Automatic two-month extension date for US citizens living outside the US, under the IRS rules for taxpayers abroad. A statement explaining why you qualify goes with the return.
7. 31 July 2027. Second UK payment on account for 2026 to 2027. 31 July 2027 is a Saturday, so the same working-day rule applies.
8. 15 October 2027. Extended US return deadline with Form 4868, and the automatically extended FBAR deadline.

Why the January deadline matters for the US return

The UK tax settled on 31 January 2027 is the tax that supports a US foreign tax credit, so its timing decides which US return it lands on. IRS Publication 514 gives two methods.

Accrual method

Publication 514 says an accrual-basis taxpayer claims the foreign tax credit in the year the tax accrues, and that foreign taxes generally accrue on the last day of the foreign tax year for which the foreign return is filed. UK tax for the year ended 5 April 2026 therefore generally accrues on 5 April 2026 and belongs on the 2026 US return, which is due in April 2027. A cash-basis individual can choose the accrual method by ticking the "Accrued" box on Form 1116, and Publication 514 says that choice must be made on a timely filed original return, not an amended one.

The consequence for timing is practical. If the 2026 US return is to claim UK tax for 2025 to 2026, the UK figure should be final before the US return is filed. Finishing the UK return by 31 January 2027 gives the US preparer a settled number in good time for 15 April or 15 June.

Cash method

A cash-basis filer claims the credit in the year the tax is paid. The 31 January 2027 payment then counts on the 2027 US return, filed in 2028, together with the July 2027 payment on account. The balancing payment and the payment on account are UK tax for different UK years, which is one reason many dual filers find the cash method harder to reconcile than the accrual method.

When the UK figure changes later

Publication 514 calls a change in your foreign tax liability a foreign tax redetermination; if it changes your US tax, you generally have to file Form 1040-X. It also says that accrued taxes not paid within 24 months after the end of the year in which they were claimed must be taken out of the credit. Filing and paying the UK return on time keeps both problems away. Our guide to foreign tax credit relief for UK tax covers the Form 1116 side in more detail.

Who is caught by the Self Assessment deadline 2027 as a dual filer?

Any American resident in the UK who has to file a UK return for 2025 to 2026, plus British nationals in the US with UK income. In practice that usually means people with:

• UK self-employment or partnership income;
• UK or overseas rental income;
• foreign income or gains to report on the SA106 foreign pages, such as US dividends, interest or a US pension;
• capital gains above the reporting limits, or untaxed income that PAYE does not cover;
• a year of arrival or departure, where split-year treatment needs to be claimed on the SA109.

Non-residents have a further constraint. GOV.UK says HMRC's own online service cannot be used to report income if you are non-resident, so a non-resident who wants the January date must file through commercial software or an agent.

The 2025/26 return also decides Making Tax Digital from April 2027

The return filed by 31 January 2027 has a second job. GOV.UK's Making Tax Digital for Income Tax eligibility guidance says sole traders and landlords with qualifying income over £30,000 for 2025 to 2026 must use Making Tax Digital from 6 April 2027. Qualifying income is gross self-employment and property income before expenses, not profit. For UK residents it includes foreign property, so an American in London who lets a house in Ohio counts that rent. For non-residents, only UK property income and self-employment income declared on the UK return count.

For those who started on 6 April 2026 at the £50,000 threshold, the first quarterly update for 2026 to 2027 was due on 7 August 2026, and the second is due on 7 November 2026. GOV.UK says HMRC will not apply penalty points for late quarterly updates in 2026 to 2027, but the annual return is still required. Our landlord service page covers the property side.

What if you miss 31 January 2027?

Filing late and paying late are penalised separately. GOV.UK lists the Self Assessment penalties:

How late	Late filing	Late payment
1 day	£100	Interest starts
30 days	—	5% of tax unpaid
3 months	£10 a day, up to £900	—
6 months	5% of tax due or £300, whichever is greater	A further 5% of tax unpaid
12 months	Another 5% or £300, whichever is greater	A further 5% of tax unpaid

Late payment interest is set at the Bank of England base rate plus 4%; HMRC publishes the current figure in its table of interest rates. You can appeal a penalty if you have a reasonable excuse, and if you cannot pay in full, HMRC offers payment plans subject to an affordability check. The full worked figures are in our guide to the late Self Assessment penalty.

A late UK return has a knock-on effect in the US. If the UK figure is not settled when the 2026 US return is filed, the foreign tax credit may have to be estimated and later corrected on Form 1040-X.

What people get wrong about the January deadline

"The deadline moves to Monday because it is a Sunday." It does not. The return is due by 11:59pm on Sunday 31 January 2027, and slower payment methods must arrive by Friday 29 January.

"I only owe for last year." The January payment often includes the first payment on account for the current year, which can make it half as large again as expected.

"My US extension covers the UK too." It does not. A US extension to June or October has no effect on HMRC's dates, and the IRS charges interest from 15 April on unpaid US tax even under an extension.

"I'll do the US return first and the UK one later." For most Americans in the UK it works the other way round: the UK return produces the tax figure the US foreign tax credit relies on.

"The UK tax I pay in January goes on next year's US return." Only for cash-basis filers. Under the accrual method in Publication 514, the 2025 to 2026 UK tax generally belongs on the 2026 US return.

Getting both returns done on time

The simplest order for a dual filer is to finish the UK return for 2025 to 2026 well before 31 January 2027, pay by 29 January unless paying by Faster Payments or card, and hand the final UK figures to whoever prepares the 2026 US return. Check whether the 2025 to 2026 figures bring you into Making Tax Digital from April 2027, and diarise 31 July 2027 for the second payment on account.

US/UK Cross Border Tax — US CPAs and UK tax advisers working as one team; London, Manchester, New York, San Francisco. Our UK Self Assessment service files returns ahead of the Self Assessment deadline 2027 and prepares the US return from the same figures. See how we work with Americans in the UK, or get in touch to plan both returns.