Should I prepare my US or my UK tax return first?

Prepare the UK Self Assessment computation first in almost every case. Form 1116 needs a figure for foreign taxes paid or accrued before the foreign tax credit can be calculated, and that figure only exists once the UK liability is computed. The calendar supports it: GOV.UK sets the online Self Assessment deadline at 31 January following the end of the UK tax year, while the IRS gives taxpayers whose tax home is abroad an automatic two month extension to 15 June. The exceptions are years where UK residence starts or ends part way through, where split year treatment applies, or where a UK figure itself depends on a US number. In those cases you draft both computations, reconcile them against each other, and only then finalise.

How do I claim UK tax on my US return when the tax years are different?

You claim it on Form 1116, and the tax year mismatch is handled by whichever basis you use. On the paid basis you credit the UK tax you actually paid during the US calendar year, whichever UK year it related to, which means PAYE deductions, payments on account and balancing payments all count by their payment date. On the accrued basis you credit the UK liability for the UK tax year that ended within the US calendar year, because foreign taxes generally accrue on the last day of the foreign tax year and 5 April always falls inside a US calendar year. Where you need to attribute UK tax to the income reported in a particular calendar year, apportion the UK year across the two US years it touches using day count or actual payroll records, and apportion income and tax on the same basis.

Is it better to use the paid basis or the accrued basis on Form 1116 for UK tax?

There is no universally better answer, but the accrued basis is far better suited to the UK mismatch and is under-used. It pulls the entire UK liability for the year ended 5 April into a single identifiable US tax year, removing the apportionment exercise and removing the distorting effect of UK payment dates. The cost is permanence. IRS Publication 514 states that the election is made by checking the box marked Accrued in Part II of Form 1116 on a timely filed original return, that it cannot be made on an amended return, that it must be followed in all later years, and that it applies to all foreign taxes qualifying for the credit. It also changes your exchange rate rule and exposes you to the rule requiring accrued taxes to be paid within 24 months of the close of the relevant year.

What extension do I use if my UK tax figure is not final when the US return is due?

Use the extension ladder in IRS Publication 54, not Form 2350. Taxpayers whose tax home is abroad get an automatic two month extension to 15 June, claimed by attaching a statement to the return. Form 4868, filed by that 15 June date, extends to 15 October. A discretionary additional two months to 15 December can be requested by sending the IRS a letter explaining the reason, sent by 15 October. That takes you past the 31 January UK Self Assessment deadline. Form 2350 is a common wrong turn here: it is for taxpayers expecting to qualify for the foreign earned income exclusion or housing exclusion who cannot yet meet the bona fide residence or physical presence test, not for taxpayers waiting on a foreign tax figure. In every case, an extension of time to file is not an extension of time to pay, and interest runs on unpaid tax from the regular due date.

Which US tax year do UK payments on account belong to?

On the paid basis they belong to the US calendar year in which they were actually paid, regardless of which UK year they relate to. GOV.UK sets payments on account at 31 January and 31 July, each normally half of the previous year's liability, with any balancing payment due the following 31 January. That means one US calendar year commonly absorbs a balancing payment for one UK year, a first payment on account for the next, a second payment on account in July, and twelve months of PAYE, so cash relating to three UK years can land in a single Form 1116. On the accrued basis the payment dates become irrelevant to the credit, because the liability is credited in the US year in which the UK tax year ended, though the payments still matter for the 24 month payment rule and for redetermination tracking.

US UK Tax Returns Preparation: Mismatched Tax Years

Q: What happens if I actually paid less UK tax than the credit I claimed?

You have a foreign tax redetermination under section 905(c) and a reporting duty that does not go away. IRS Publication 514 explains that where you pay less foreign tax than you claimed a credit for, you must generally file a notification by the due date, including extensions, of your original return. Where your US tax liability has to be recomputed, you file Form 1040-X for the year in which the original tax was paid or accrued, with a revised Form 1116. Schedule C (Form 1116) is separately used to report redeterminations occurring in the current year that relate to prior years, attached to the return for the year the redetermination occurs. If you accrued UK tax that remains unpaid more than 24 months after the close of the year it relates to, that unpaid portion is treated as a redetermination and no credit is allowed until it is actually paid.

US UK tax returns preparation breaks down at exactly one point for almost every American living in Britain: the US tax year ends on 31 December, the UK tax year ends on 5 April, and the tax you hand to HMRC almost never lands in the US calendar year it belongs to. The fix is not exotic, but it is precise. You choose deliberately between claiming foreign tax credits on the paid basis and electing the accrued basis on Form 1116. You apportion any UK liability that straddles two US calendar years on a defensible and consistent method. You use the filing extensions available to taxpayers abroad so that the US return is not filed before the UK figure is known. And you accept a standing duty to tell the IRS when the tax actually paid turns out to differ from the tax you claimed. Get those four decisions right and the mismatch becomes an administrative chore. Get them wrong and you manufacture unusable excess credits in one year, an unrelieved US liability in the next, and an amended return you never needed to file.

Why do the US and UK tax years refuse to line up?

The UK tax year runs from 6 April to 5 April. GOV.UK states the dates plainly in its Self Assessment guidance, and sets the online filing and payment deadline at 31 January following the end of that tax year, with 31 October for paper returns. The US individual tax year, for essentially every private client, is the calendar year ending 31 December. Neither authority adjusts to the other. The double taxation agreement between the two countries allocates taxing rights and relieves double taxation, but it does not synchronise accounting periods, and no treaty article permits you to file a UK-year Form 1040.

The consequence is structural rather than cosmetic. Your Form 1040 must report worldwide income arising between 1 January and 31 December. Your Self Assessment return reports income for a period beginning in April. A single UK employment, partnership profit share, property portfolio or investment income stream is therefore sliced differently by each authority, and the tax attaching to it is fixed on a UK timetable while the credit for it is claimed on a US one. Every downstream problem in this article descends from that one fact.

For modest filers the effect is often invisible, because the credit is generous enough to wipe out the US liability regardless of which year it lands in. For a high earner it is anything but invisible. Once you are into the higher and additional rate bands in the UK, with variable bonus, dividend, partnership and capital gains elements moving year to year, the gap between the year the tax arises and the year it is creditable moves real money. It moves it in a direction that produces excess credits you cannot use now and a US balance due you did not budget for.

US UK tax returns preparation: which return do you prepare first?

You prepare the UK Self Assessment return first, or at minimum you compute it first. The reason is mechanical rather than strategic. Form 1116 requires a figure for foreign taxes paid or accrued, and that figure comes out of the UK computation. You cannot finalise a credit for a liability you have not calculated, and an estimated foreign tax figure inserted to meet a US deadline is the most common origin of the amended returns we are later asked to clean up.

The calendar cooperates. GOV.UK requires the online Self Assessment return for the year ended 5 April to be filed by the following 31 January. The IRS grants US citizens and resident aliens whose tax home is abroad an automatic two month extension to 15 June, claimed by attaching a statement to the return confirming that you qualify. So the UK return for a year that ended in April is due the following January, comfortably ahead of the June US deadline for the calendar year that ended the preceding December.

The order is not absolute. Where UK residence is being established or broken part way through a year, where split year treatment is in play, or where a UK figure itself depends on a US number, you may have to iterate: draft both computations, reconcile them, then finalise. But for a settled UK-resident American the default sequence is UK computation, then US computation, then US filing. Reversing it means guessing at the credit.

Compute the UK Self Assessment liability for the tax year ended 5 April first, because Form 1116 cannot be completed without a foreign tax figure.
Extract the UK payment record separately from the UK liability record. What you owe for a UK year and what cash you actually handed over during a calendar period are different numbers, and they feed different bases.
Decide the paid versus accrued basis before the first Form 1116 is filed rather than after, because the accrual election cannot be made on an amended return.
Extend the US return rather than filing an estimate you will have to correct, whenever the UK figure is not yet final.
Reconcile foreign tax credit carryovers on Schedule B (Form 1116) every single year, instead of reconstructing a decade of history under audit pressure.
Keep the apportionment method constant year on year, so that a reviewer sees a consistent system rather than an annual improvisation.

What is the difference between the paid basis and the accrued basis on Form 1116?

The paid basis claims the foreign tax credit in the US tax year in which you actually hand the money to HMRC. The accrued basis claims it in the US tax year in which the liability accrues, which for a UK liability is generally the last day of the UK tax year, 5 April. That is the whole distinction, and it is the most consequential choice in this area of US UK tax returns preparation.

Most individuals are cash method taxpayers and default to the paid basis without ever registering that a choice existed. IRS Publication 514 explains that a cash method taxpayer may instead elect to claim the credit in the year the taxes accrue, by checking the box marked Accrued in Part II of Form 1116, and that the election must be made on a timely filed original return. Publication 514 is explicit that the choice cannot be made on an amended return. That single sentence is why the decision has to be taken during preparation and not during a later review.

The accrued basis is the more powerful tool against the mismatch, and it is badly under-used. Foreign income taxes generally accrue when all the events have occurred that fix the amount and your liability to pay it, which is normally the last day of the foreign tax year. The long-standing IRS position is that the foreign tax liability for a foreign tax year is creditable in the US tax year within which that foreign year ends. Because 5 April always falls inside a US calendar year, the entire UK liability for the year ended 5 April 2026 accrues in US tax year 2026 and is claimed in one place, on the 2026 Form 1040. No day count. No split across two returns. No dependence on when HMRC happened to take the cash.

The commitment attached to that election is real, which is why it deserves a documented decision rather than a software default set by whoever prepared your first return abroad.

The election binds all later years. Publication 514 states that once made you must follow it in later years and take the credit in the year the taxes accrue.
It applies to all foreign taxes qualifying for the credit, not only UK tax and not only one income category.
It must be made on a timely filed original return. An amended return will not carry it, and there is no informal route back in.
It changes your currency translation rule. Accrued taxes generally use the average exchange rate for the tax year to which the taxes relate, rather than the rate on each individual payment date.
It exposes you to the accrued but unpaid rules, including the requirement that accrued taxes actually be paid within 24 months after the close of the year to which they relate.
The transition year needs care, so that UK tax is neither counted twice nor lost in the gap between the final paid basis year and the first accrued basis year.

How do you apportion a UK tax liability across two US calendar years?

If you remain on the paid basis, no apportionment of the liability itself is strictly required, because you simply credit what you actually paid during the calendar year. Apportionment becomes necessary when you are matching UK tax to the UK-source income reported in a particular US year. To run the Form 1116 limitation you need foreign source taxable income for the calendar year, and for the credit to be coherent to a reviewer you want the tax to track that income rather than float free of it.

The defensible methods are all variations on one idea: allocate the UK year across the two US calendar years it touches, and allocate the tax on the same basis you allocate the income. Day count is the simplest and is usually adequate for salary. Actual payroll and payment records are better where income is lumpy, because a March bonus does not behave like an even monthly salary and a day-count split will misstate the tax attaching to it. What matters most is that the method is reasonable, that income and tax are apportioned consistently with each other, and that the same method is used year after year.

Take an illustrative case. Marcus Halloway is a fictional US citizen working in a senior banking role in London. Every figure below is round and illustrative only, chosen to expose the arithmetic rather than to state any rate or threshold. His UK liability for the tax year 6 April 2024 to 5 April 2025 comes to GBP 400,000. That UK year contains 365 days, of which 270 fall in US calendar year 2024, running from 6 April to 31 December 2024, and 95 fall in US calendar year 2025, running from 1 January to 5 April 2025.

On a straight day count, roughly 74 per cent of that UK year sits inside US 2024 and roughly 26 per cent inside US 2025. Applying those proportions, approximately GBP 295,900 of the UK liability is attributable to the 2024 US calendar year and approximately GBP 104,100 to 2025. Marcus also has a UK liability for the year ended 5 April 2026, and the portion of that year running from 6 April 2025 to 31 December 2025 lands in US 2025 as well. So his 2025 Form 1040 carries the tail of one UK year and the front of the next. Each sterling figure is then translated into USD under whichever rule matches his elected basis.

Now compare the accrued basis on the same facts. Under the accrual election the whole GBP 400,000 for the UK year ended 5 April 2025 accrues on that date. 5 April 2025 falls in US calendar year 2025, so the entire amount is claimed on the 2025 Form 1040 and the apportionment exercise disappears. What does not disappear is that the income on that 2025 Form 1040 is still calendar-year income, so the limitation fraction still compares a UK-year tax against calendar-year foreign source income. That residual mismatch is the part almost no guide mentions, and we return to it below.

What if UK tax is not finally determined before the US return is due?

This is the timing problem that generates most avoidable amended returns. The UK liability for a year ended 5 April is not finally determined until the Self Assessment return is filed and processed, and GOV.UK allows that until the following 31 January. Meanwhile the US return for the calendar year that ended the previous 31 December falls due in April, or June for taxpayers abroad. For the second, later UK year touching that US calendar year, the final figure simply does not exist yet.

The correct tool is time, not estimation. IRS Publication 54 sets out the ladder available to a taxpayer whose tax home is abroad. First, the automatic two month extension to 15 June, claimed by attaching a statement to the return explaining which situation qualifies you. Second, a further extension to 15 October, obtained by filing Form 4868 by that 15 June date. Third, a discretionary additional two months to 15 December, requested by sending the IRS a letter explaining why the extra time is needed, sent by 15 October. That ladder carries a calendar-year US return past the 31 January UK filing deadline, which is normally enough to work from final HMRC figures.

One correction deserves to be made loudly, because it is the most common misconception in this whole area. Form 2350 is not a foreign tax credit extension. IRS guidance is clear that Form 2350 is for US citizens and resident aliens abroad who expect to qualify for the foreign earned income exclusion or the foreign housing exclusion or deduction, but who will not meet the bona fide residence test or the physical presence test until after the return is due. The extension it grants is generally around 30 days beyond the date you can reasonably expect to qualify. If your problem is that the HMRC number is not ready, Form 2350 is the wrong instrument. Form 4868 followed by the December letter is the right one.

Whichever extension you use, an extension of time to file is never an extension of time to pay. Publication 54 is explicit that interest is charged on any tax not paid by the regular due date of the return. For a high earner deferring a US return into December, that interest cost is not trivial, and it should be met with a payment on account of the projected US liability rather than absorbed as a surprise on assessment.

How do UK payments on account and balancing payments map onto US credit timing?

Under the paid basis, this is where the mismatch does most of its damage. GOV.UK explains that payments on account are two instalments towards the next year's bill, due on 31 January and 31 July, each normally half of the previous year's liability, with any balancing payment for the shortfall due the following 31 January. Payments on account are not required where the previous year's tax bill was under GBP 1,000, or where more than 80 per cent of tax was collected at source, and a taxpayer expecting a lower year can apply to reduce them using form SA303.

Read that schedule against a US calendar year and the distortion is obvious. On 31 January the taxpayer pays a balancing payment for one UK year and simultaneously a first payment on account for the next. On 31 July the second payment on account falls due. Both of those dates sit inside the same US calendar year, and PAYE deducted month by month sits there too. A single US calendar year can therefore absorb cash relating to three different UK tax years.

The result is an artificial pattern: excess credit in the heavy year and unrelieved US tax in the light year that follows, particularly where payments on account were reduced under SA303 or where UK income fell. Nothing about the underlying economics changed. It is purely an artefact of cash timing. This is the strongest single argument for at least modelling the accrued basis where a client has a large and volatile UK liability, and the best explanation for why a foreign tax credit carryover schedule that looks irrational usually is not.

PAYE and any coding adjustments deducted between January and December of the US calendar year.
The 31 January balancing payment for the UK year that ended the previous 5 April.
The 31 January first payment on account for the UK year then in progress.
The 31 July second payment on account for that same in-progress UK year.
Any voluntary payment, late payment, interest or HMRC-directed payment made during the period.
Repayments received from HMRC, which reduce creditable foreign tax and must be tracked with the same care as payments.

What happens to excess foreign tax credits you cannot use?

Where qualified foreign taxes exceed the Form 1116 limitation for the year, the excess is not immediately lost. IRS Publication 514 provides a one year carryback and then a ten year carryover of the unused foreign tax. The unused amount is applied first to the preceding tax year, up to the excess limit available there, and then carried forward. The carryover is tracked separately for each income category, because the limitation itself is computed category by category.

The limitation is the constraint that actually bites. As the IRS explains, the credit is capped at your US tax liability multiplied by a fraction whose numerator is foreign source taxable income and whose denominator is total taxable income from all sources, and the credit allowed is the lesser of the foreign tax and that cap. Bunching UK tax into one calendar year through cash timing does nothing to raise the numerator. It simply pushes more tax above the cap, which is exactly how a timing artefact converts into a permanent-feeling carryover.

Two further limits matter during preparation. Carryovers are not available for the section 951A income category. And you cannot carry credits into or out of a year in which you chose to deduct foreign taxes rather than credit them, so a casual switch to the deduction in a single low year can strand a carryover generated elsewhere. Schedule B (Form 1116) exists precisely to reconcile the prior year carryover with the current year carryover, and it should be prepared contemporaneously every year rather than rebuilt from memory when the credit is finally used.

What is the re-determination duty when the tax actually paid differs?

A foreign tax redetermination arises when the foreign tax you eventually pay differs from the amount you claimed. That can happen because HMRC amended an assessment, because you amended the Self Assessment return, because a repayment came back, or because an amount you accrued was never actually paid. Section 905(c) treats this as an event carrying its own reporting duty. Publication 514 confirms that where you pay less foreign tax than you claimed a credit for, you must in most cases file a notification by the due date, including extensions, of your original return.

There are two distinct mechanics and they are frequently confused. Where a redetermination requires your US tax liability to be recomputed, you file an amended return, Form 1040-X, for the year in which the original tax was paid or accrued, with a revised Form 1116 attached. Separately, Schedule C (Form 1116) is used to report foreign tax redeterminations that occur in the current tax year but relate to prior tax years, and it is attached to the return for the year in which the redetermination occurs.

The accrued basis makes this reporting more likely rather than less, and that is the honest trade-off against its structural elegance. If you accrue a UK liability and then fail to pay it within 24 months after the close of the year to which it relates, the unpaid portion gives rise to a redetermination and no credit is allowed for it until it is actually paid. A UK-resident client with an open HMRC enquiry, a payment plan, or a disputed assessment needs that 24 month clock diarised in the compliance file.

Where UK tax is genuinely contested, the credit is not available at all until the contest is resolved and the liability finally determined. Publication 514 describes an election to take a provisional credit for a portion of a contested foreign income tax liability, made by filing Form 7204 with the return and followed by Schedule C (Form 1116) filings until the matter is resolved. That is a specialist route rather than a routine one, but it exists, and it is preferable to claiming a credit for a number that is still under argument.

What records make a UK foreign tax credit defensible?

The credit is only ever as good as the file behind it. For a wealthy filer with employment, partnership, property and investment income running through both systems, the record set is not housekeeping. It is the evidence that allows a two-country position to survive review years later, often after the preparer who built it has changed. IRS practice looks for the receipt for the foreign tax payment or the foreign tax return itself, with secondary evidence such as a copy of the payment where direct evidence genuinely cannot be produced, and a certified translation where a document is not in English.

The filed Self Assessment return and the HMRC tax calculation for each UK year, being the SA302 or its online equivalent.
The HMRC statement of account showing every payment and every repayment with its actual date, which is the primary source document for the paid basis.
P60 and P11D documents, partnership statements, and PAYE coding notices that explain why a withheld figure moved during the year.
A schedule of exchange rates used, with the source recorded, applied on the basis that matches your election: payment date rates for the paid basis, and the average rate for the year to which the tax relates for the accrued basis.
The apportionment working itself, showing the day count or payroll basis used to split each UK year across the two US calendar years it touches.
A rolling foreign tax credit carryover schedule by income category, tied each year to Schedule B (Form 1116).
A file note recording which basis was elected, the date the accrual election was made, and the reasoning, so consistency can be demonstrated a decade later.
The Self Assessment foreign pages, SA106, and their HMRC notes where Foreign Tax Credit Relief has been claimed in the UK on non-UK income.

Two traps that survive the obvious fixes

The first trap is that the accrual election fixes the tax side of the mismatch but leaves the income side untouched. Once elected, the UK liability for a year ended 5 April is credited cleanly in the US year containing that date. But the income on the Form 1040 remains calendar-year income, and the Form 1116 limitation still divides calendar-year foreign source taxable income by calendar-year total taxable income. A year of sharply rising or falling UK income therefore still produces a limitation that does not correspond to the tax, even on the accrued basis. Anyone who tells you the accrual election eliminates the mismatch is describing half of it.

The second trap is that the permanence of the election collides with mobility. The accrual election applies to all foreign taxes qualifying for the credit and must be followed in all later years. A client who elects accrual while UK resident and then relocates to a jurisdiction whose tax year is the calendar year, or takes on income taxed under an entirely different foreign regime, carries that election with them. That is not a reason to avoid it. It is a reason to make it as a documented decision about a whole cross-border career, rather than as a keystroke on a single Form 1116.

There is a quieter third trap, and it is sterling. On the paid basis, each UK payment translates at the exchange rate in effect on its own payment date. On the accrued basis, the general rule is the average rate for the tax year to which the tax relates. Two economically identical UK liabilities can therefore produce materially different USD credits purely because of currency movement across the period. For a filer with a large UK liability, that FX effect is not a rounding item, and it should be modelled before the basis is chosen rather than discovered afterwards in a carryover schedule.

None of this is complicated so much as it is disciplined. Compute the UK return first. Choose the basis deliberately and record the choice. Apportion income and tax on the same method and keep that method stable. Extend rather than estimate. Reconcile the carryover annually. Treat the redetermination duty as a standing obligation rather than an ambush. The mismatch between 31 December and 5 April is permanent, and no amount of planning will move either date. The damage that mismatch does to a foreign tax credit, on the other hand, is entirely within the control of whoever prepares the two returns.