UK Tax Year vs US Tax Year: Handling the 6 April / 1 January Mismatch

UK tax year vs US tax year: the UK tax year runs from 6 April to 5 April, and the US tax year for an individual is the calendar year, 1 January to 31 December. Anyone who files in both countries has to re-cut income by date for each return and move foreign tax credits into the year each country expects.

The mismatch is roughly three months, but it touches almost every line of a cross-border return. Your P60 covers the wrong twelve months for the IRS. Your US brokerage statement covers the wrong twelve months for HMRC. The tax you paid in one country has to be matched to income reported in a different year in the other. This guide sets out how each side expects that to be done, with the official sources linked beside each rule.

What is the difference between the UK tax year and the US tax year?

The UK tax year for individuals runs from 6 April to the following 5 April, and the US tax year for an individual is the calendar year. GOV.UK's Self Assessment deadlines page describes the most recent UK tax year as 6 April 2025 to 5 April 2026, written 2025/26. The US return for 2025 covers 1 January to 31 December 2025.

So each UK tax year straddles two US years, and each US year straddles two UK tax years. The table shows how the 2026 calendar year is divided.

Period	UK tax year	US tax year
6 April 2025 to 31 December 2025	2025/26	2025
1 January 2026 to 5 April 2026	2025/26	2026
6 April 2026 to 31 December 2026	2026/27	2026
1 January 2027 to 5 April 2027	2026/27	2027

The awkward window is 1 January to 5 April. Anything received in those 95 days belongs to the earlier UK tax year and the later US year. A bonus paid in March, a dividend paid in February or a property sale completed in January will always sit in different "years" on the two returns.

Why the UK tax year vs US tax year mismatch matters

If each country taxed you alone, the dates would be a curiosity. They matter because the US taxes its citizens and green card holders on worldwide income wherever they live, and the UK taxes its residents on worldwide income too. The same income is reported twice, and double tax is removed by credits. A credit only works when the tax paid in one country can be matched to the income taxed in the other, and the two countries group that income into different twelve-month blocks.

There are three practical consequences:

• Income has to be rebuilt by date. UK documents (P60, bank interest certificates, platform tax packs) run to 5 April. US documents (Form 1099, Schedule K-1) run to 31 December. Each return needs the other country's income re-cut to its own year.
• Tax credits arrive in a different year from the income. UK tax on a slice of income may be paid, or may legally accrue, in a later US year than the one in which the income is reported.
• The deadlines interleave. The US return for a calendar year normally falls due before the UK return that covers most of the same income has been filed.

This is the core of what cross-border tax advice on the UK tax year vs US tax year problem involves: one set of working papers that reconciles both years, so each return is prepared from the same underlying figures.

How do you report UK salary on a US return when the P60 runs to 5 April?

You report the pay you actually received between 1 January and 31 December, taken from payslips by pay date, not the figure on the P60. GOV.UK says a P60 shows the tax you have paid on your salary in the tax year (6 April to 5 April), and that employers must provide it by 31 May. It is a UK-year document and nothing on it can be lifted straight onto Form 1040.

Illustrative example: Sarah, a US citizen living in Leeds, earns £8,000 a month, paid on the last working day. In March 2026 she receives a £20,000 bonus. From April 2026 her pay rises to £9,000 a month. Her 2025/26 P60 shows £116,000 (twelve months at £8,000 plus the bonus). Her 2026/27 P60 will show £108,000. Her 2026 US return needs neither figure. It needs January to March 2026 at £8,000 (£24,000), the £20,000 bonus, and April to December 2026 at £9,000 (£81,000): £125,000 in total, converted to dollars.

Neither P60 shows £125,000, and no UK document ever will. The same rebuild applies to the PAYE tax deducted, to pension contributions and to benefits in kind. Keep every payslip; in a dual-filing household they are the primary record.

Converting pounds to dollars

The IRS says on its yearly average currency exchange rates page that it has no official exchange rate and generally accepts any posted exchange rate that is used consistently. A yearly average is commonly used for income received evenly through the year, and a spot rate for a one-off item such as a property sale. Whatever rate is chosen for the US return, it must be the rate for the US calendar year, not for the UK tax year.

Investment income and gains

Dividends, interest and capital gains follow the same logic: the date of payment or disposal decides the year in each country. A UK investment platform's annual tax pack runs to 5 April and has to be re-cut to 31 December for the US return. A US broker's Form 1099 runs to 31 December and has to be re-cut to 5 April for the SA106 foreign pages of the UK return. Transaction-level statements, not annual summaries, are what both returns are built from.

Foreign tax credits: which UK tax belongs to which US year?

This is where the mismatch costs money if it is handled badly. The US foreign tax credit is claimed on Form 1116, and IRS Publication 514 (2025 revision) allows two methods of deciding which year a foreign tax belongs to.

	Paid method	Accrued method
UK tax credited on the 2026 US return	UK tax actually paid between 1 January and 31 December 2026: PAYE deducted on 2026 pay dates, plus Self Assessment payments made in 2026	The UK liability for the tax year ended 5 April 2026 (2025/26), because Publication 514 says foreign tax generally accrues on the last day of the foreign tax year
Exchange rate (Publication 514)	The rate on the date the tax was paid	Generally the average rate for the tax year to which the tax relates
If the final UK bill differs	Only tax actually paid is claimed, though a later UK refund of that tax still has to be reported to the IRS	A foreign tax redetermination; Publication 514 requires Form 1040-X if accrued tax differs when paid, or is not paid within 24 months
Flexibility	Default for cash-basis individuals	Elected on a timely filed original return; once chosen it must be followed in all later years

Neither method produces a perfect match. Under the accrued method, Sarah's 2026 US return takes credit for her whole 2025/26 UK liability, most of which relates to income she reported on her 2025 US return. Under the paid method, her 2026 credit includes the balancing payment for 2024/25 that she made on 31 January 2026, which relates to income from as far back as April 2024.

In steady years this evens out, because each year's credit is one year's worth of UK tax either way. It stops evening out when income changes sharply: the first year in the UK, a large bonus, a redundancy payment or a one-off capital gain.

Carrying credits between years

Publication 514 says unused foreign taxes are ordinarily carried back to the preceding tax year and then forward to the 10 following years. The one-year carryback is what repairs most timing gaps, but it only reaches back one year.

That limit catches people out with one-off gains. Take a gain on shares realised in May 2026. The US taxes it on the 2026 return. The UK taxes it in 2026/27, and for a gain that is not on UK residential property the tax is normally paid through Self Assessment on 31 January 2028. Under the paid method that is a 2028 credit, and a one-year carryback reaches 2027, not 2026. Under the accrued method the UK tax accrues on 5 April 2027, a 2027 credit, which a one-year carryback can bring to 2026. The method chosen years earlier can decide whether that gain is relieved or taxed twice. UK residential property is different again, because GOV.UK requires the Capital Gains Tax to be reported and paid within 60 days of completion.

How does HMRC handle US tax that is charged for a calendar year?

HMRC apportions it by time. For a UK resident claiming Foreign Tax Credit Relief in the UK for US tax paid, the US tax is worked out for a calendar year but the UK return covers 6 April to 5 April. HMRC's International Manual at INTM161220 says that where the foreign basis period is different from the UK basis, any apportionment should generally be made in proportion to the number of days in the relevant periods.

HMRC's own example uses foreign rents for the year ended 5 April 2023: three quarters (270 days) of the 2022 foreign tax and one quarter (95 days) of the 2023 foreign tax are available for credit against UK tax for 2022/23. Applied to the 2025/26 UK tax year, the same arithmetic takes 270 days' worth of the US tax for 2025 and 95 days' worth of the US tax for 2026.

INTM161220 also says an alternative time-apportionment basis suggested by the taxpayer can be accepted, provided it is reasonable and applied consistently, for example by weeks or months. Two points follow in practice:

• Apportionment is for tax charged by assessment on a year's income, such as US tax on rental profits. Where US tax is withheld from a specific payment, such as a dividend, the tax simply follows that payment into whichever UK tax year it falls.
• The second US year's tax is often not known when the UK return is due. A UK return for 2025/26, due by 31 January 2027, needs a slice of 2026 US tax that may not be finalised until later in 2027. Provisional figures, corrected by amendment, are a normal part of dual filing.

A combined UK and US deadline calendar for 2026

Because the years are offset, the filing dates leapfrog each other. These are the dates for an American resident in the UK during calendar 2026, each taken from GOV.UK or the IRS.

1. 31 January 2026. UK online return and balancing payment for 2024/25, plus the first payment on account for 2025/26. GOV.UK says payments on account are due by midnight on 31 January and 31 July.
2. 5 April 2026. The UK 2025/26 tax year ends. Under the accrued method, this is the date the year's UK tax generally accrues for US purposes.
3. 15 April 2026. Regular due date for the 2025 US return and the 2025 FBAR. The IRS says interest runs from this date on any US tax unpaid, even where a filing extension applies.
4. 31 May 2026. Employers must have provided the 2025/26 P60.
5. 15 June 2026. The automatic 2-month extension for US citizens and resident aliens living outside the United States.
6. 31 July 2026. Second UK payment on account for 2025/26.
7. 5 October 2026. Deadline to tell HMRC you need to file a return for 2025/26 if you have not filed before.
8. 15 October 2026. Extended US due date where Form 4868 was filed, per IRS Publication 54; the FBAR's automatic extension also ends on this date.
9. 31 October 2026. UK paper return deadline for 2025/26.
10. 31 January 2027. UK online return and payment for 2025/26.

Publication 54 also describes a discretionary further extension to 15 December for taxpayers who are out of the country, requested by letter. Our guide to the US expat tax extension deadlines for 2026 explains how the June, October and December dates fit together, and the HMRC payment on account guide covers the January and July instalments.

Notice the order. The 2025 US return is due in spring or autumn 2026, but the UK return covering April to December 2025 is not due until 31 January 2027. Many dual filers extend the US return to October and prepare the UK return early, in the summer, so that final UK figures exist before the US return is signed.

What people get wrong about the two tax years

Copying the P60 onto Form 1040

It is the most common error in self-prepared returns. The P60 total is for the wrong twelve months, and in a year with a pay rise, a bonus or a job change the difference is material.

Switching credit methods from year to year

Publication 514 is explicit that a cash-basis taxpayer who chooses to credit foreign taxes when they accrue must follow that choice in all later years, and that the election is made on a timely filed original return. Check which box was ticked on your earliest Form 1116 before preparing this year's.

Forgetting that the FBAR and the exclusion use US dates

The IRS says the FBAR looks at whether foreign accounts exceeded $10,000 in aggregate at any time during the calendar year. The foreign earned income exclusion is also worked out for the US year, although the physical presence test can use any period of 12 consecutive months containing 330 full days abroad, which helps in the year of arrival.

Assuming a move splits both years the same way

The UK can divide the tax year of arrival or departure into a UK part and an overseas part under split year treatment. The US does no such thing for its citizens, who are taxed on worldwide income for the whole calendar year wherever they live. In a year of arrival, part of the US year has no UK tax to credit against it at all.

Treating the two returns as separate jobs

The figures on a UK return and a US return should reconcile to one set of transactions. When two preparers work from different documents, the 95 days between 1 January and 5 April are where income is counted twice or not at all. Our overview of UK Self Assessment for Americans explains the order in which the two returns are best prepared.

A year-end routine that makes the mismatch manageable

1. Keep transaction-level records. Payslips, dated dividend and interest entries, and contract notes for every sale. Annual summaries from either country cover the wrong period for the other.
2. Cut the records twice. Once to 31 December for the IRS and once to 5 April for HMRC, from the same underlying data.
3. Record every tax payment with its date. PAYE by pay date, each Self Assessment payment, each US estimated payment and each withholding. The date decides the year under the paid method and the exchange rate.
4. Confirm your Form 1116 method. Paid or accrued, as elected on the first return, and apply it the same way every year.
5. Plan one-off events around both calendars. A disposal on 4 April and one on 6 April fall in different UK tax years but the same US year. Before a large sale or bonus, check where the tax and the credit will land in each country.
6. Sequence the filings. Finalise UK figures before the extended US deadline where you can, then true up the UK return for final US tax by amendment if needed.

US/UK Cross Border Tax is a firm of US CPAs and UK tax advisers working as one team, with offices in London, Manchester, New York and San Francisco. We prepare both returns from one reconciled set of working papers, which is the practical answer to the UK tax year vs US tax year problem. If you are an American living in the UK and your two returns have never been reconciled to each other, our UK Self Assessment service is a sensible place to start, or contact us to talk through your position.