Specialist US UK Tax Services: When UK Tax Changes Later
Specialist US UK tax services for filers whose UK liability shifts after the US return is lodged. Section 905(c) notification, done right. Talk to us.
One side settled, the other still moving
When HMRC changes your UK tax after the US return has already been lodged, the foreign tax credit you claimed becomes wrong retroactively. Section 905(c) makes that your problem to report, not the IRS's problem to discover: you must notify the IRS of the redetermination on Schedule C of Form 1116, and in many cases amend the earlier US year as well.
This is one of the least-understood mechanics in US-UK compliance, and it surfaces constantly in catch-up work. At Jungle Tax we see it most often in the six to eighteen months after a client thinks the hard part is over. Our Specialist US UK tax services treat the redetermination as part of the engagement, not an afterthought, because the moment the UK number moves the US filing stops being final.
What is a foreign tax redetermination, and why does a UK change cause one?
A foreign tax redetermination is a change in your foreign tax liability that affects the US foreign tax credit you have already claimed. The Internal Revenue Code treats three events as redeterminations: foreign tax that accrues in an amount different from the amount you claimed as a credit; accrued foreign tax that is not paid within a defined window after the close of the year it relates to; and foreign tax that is paid and then refunded, in whole or in part.
Read against a UK Self Assessment cycle, that definition is far broader than it looks. Almost every routine UK event that adjusts a liability after the event is, in US terms, a redetermination. An HMRC repayment following an amended return is a refund. A revised liability after an enquiry closes is a change in the amount accrued. A balancing payment settled long after the year end can fall foul of the payment-window rule. None of these feel like tax controversy to a UK filer. All of them create a US reporting duty.
The crucial point for anyone reading this from the UK side: HMRC will not tell the IRS, and the IRS will not adjust your credit for you. The obligation runs one way, and it runs to you.
Why does this happen so often in US-UK catch-up cases?
The two tax years do not line up
The UK tax year runs from 6 April to 5 April. The US tax year is the calendar year. Any UK liability credited against a US year is therefore a constructed figure, apportioned or traced across a boundary that does not exist in UK law. When the underlying UK liability later moves, the apportionment moves with it, and the constructed figure that supported your credit no longer reconciles to anything HMRC holds.
The UK filing deadline falls after the US one
A US return for a calendar year is due 15 April following, or 15 June with the automatic expatriate extension, or 15 October on extension. The UK return covering the overlapping period is not due online until the following 31 January. In a normal year, the US return is prepared using an estimate of the UK liability, and the UK figure is only finalised months later. The gap between estimate and outturn is the single most common source of redeterminations we see.
HMRC keeps its own windows open
A UK taxpayer can amend a Self Assessment return within twelve months of the 31 January filing deadline. After that, overpayment relief remains available for four years from the end of the tax year. HMRC's own assessing powers run longer still. The practical effect is that a UK liability can legitimately change years after the US return that credited it was signed and filed.
Catch-up filings are built on reconstructed numbers
In a compliance catch-up, whether through the Streamlined Foreign Offshore Procedures or a straightforward set of late returns, the UK figures are frequently reconstructed from statements, payslips and HMRC account records rather than from a return that was filed contemporaneously. When the UK position is subsequently tidied up properly, the reconstructed credits move. Anyone advising on IRS streamlined filing without planning for that second wave is only doing half the job.
Which UK events trigger a US notification?
| UK event | How it looks to HMRC | US consequence under section 905(c) |
|---|---|---|
| Amended Self Assessment return within the 12-month window | Routine correction, revised calculation issued | Redetermination in the year the change occurs; Schedule C required |
| Overpayment relief claim after the amendment window closes | Standalone claim in writing to HMRC | Refund of foreign tax; relates back to the original credit year |
| Closure notice ending an HMRC enquiry | Liability agreed or determined | Change in accrued foreign tax; may increase or decrease the credit |
| Discovery assessment raising additional UK tax | Assessment for an earlier year | Additional foreign tax; treatment differs by cash or accrual basis |
| PAYE reconciliation or P800 repayment | Automatic HMRC repayment | Refund of foreign tax, however small; still reportable |
| Balancing payment settled well after the UK year end | Late payment with interest | Potential deemed refund under the payment-window rule |
| Remittance basis position revised for an earlier year | Recomputed UK liability | Redetermination, often across several US years at once |
Note what is not on that list: a change in your US income, a correction to your US deductions, or a missed US information return. Those are ordinary amendment territory. A redetermination is specifically about the foreign tax number, and it carries its own machinery.
Do you file Schedule C, amend the earlier year, or both?
Both, more often than not, and the two filings do different jobs.
Schedule C (Form 1116) is the notification. It is attached to the US return for the year in which the redetermination occurs, and it identifies the redetermination, the years to which it relates, the separate income category, the original and revised foreign tax figures, the currency and the exchange rates used. It is filed whether or not your US tax liability actually changes. That last point catches people out: a redetermination that washes through without altering the bottom line still has to be reported.
The amended return is the correction. If the redetermination changes your US tax liability for an earlier year, you file an amended return for that year in addition to the Schedule C. One filing tells the IRS what happened; the other fixes the number.
The December 2025 revision of Schedule C separates increases from decreases across Parts I and II and adds discrete columns for tax refunded and additional tax paid, which makes the UK repayment case considerably easier to present cleanly than it was under earlier versions. The IRS publishes the current schedule and its instructions alongside the main form at About Form 1116.
What are the deadlines, and why are there two of them?
The direction of travel governs the clock, and this asymmetry is the part generalist guidance almost always misses.
Where the redetermination increases your US tax liability, the notification is due by the due date, including extensions, of the original return for the year in which the redetermination occurred. It is a hard deadline with a penalty attached, and it does not wait for you to get around to the amendment.
Where the redetermination decreases your US tax liability, you are in refund-claim territory and the ordinary limitations period applies. Critically for cross-border filers, refund claims attributable to foreign taxes benefit from an extended statutory window that is materially longer than the standard three-year rule. A UK amendment that surfaces four or five years later is very often still worth pursuing on the US side, where a purely domestic claim would be dead.
| US / IRS | UK / HMRC | |
|---|---|---|
| Routine correction window | Generally three years from filing to claim a refund | 12 months from the 31 January filing deadline |
| Extended window | Substantially longer period for refund claims attributable to foreign taxes | Overpayment relief: four years from the end of the tax year |
| Who must initiate | The taxpayer, by Schedule C and amended return | The taxpayer, by amendment or written claim |
| Reporting duty where no tax changes | Yes - Schedule C is still required | No equivalent standalone duty |
| Penalty for silence | Percentage of the deficiency, escalating monthly | Behaviour-based penalties on the underlying inaccuracy |
HMRC sets out the UK amendment and overpayment relief mechanics on its Self Assessment corrections guidance, and the underlying double taxation relief framework sits in the HMRC International Manual.
Cash basis or accrual basis: the election that governs everything
Whether you claim the foreign tax credit on the paid basis or elect to accrue is the single most consequential choice in this area, and it is usually made once, early, and never revisited. It should be.
On the paid basis, UK tax is credited in the US year in which it is actually paid. A balancing payment made in January 2027 for UK 2025/26 lands on the US 2027 return. This keeps the credit simple to evidence but pushes it into a year whose US income may bear no relationship to the UK income that generated the tax, which is where limitation problems begin.
On the accrual basis, UK tax is credited against the US year to which it relates, which produces a far better economic match and is generally the right answer for a client with steady UK employment or UK trading income. The trade-off is that an accrual is by definition an estimate until HMRC agrees it, so the accrual basis manufactures redeterminations. The election is also binding for later years once made, so it is not a decision to take casually inside a single year's engagement.
There is a genuine asymmetry buried in the mechanics that repays attention. For a taxpayer on the paid basis, additional foreign tax paid in respect of an earlier year is generally picked up in the year of payment rather than related back. But a refund of foreign tax previously credited relates back to the year in which the credit was taken. Increases and decreases therefore do not travel the same route, and a UK enquiry that produces both an additional assessment for one year and a repayment for another will require two quite different treatments in the same submission.
What happens if the UK tax goes down?
This is the common case in HNW catch-up work, because tidying up a UK position properly tends to unlock relief that was never claimed. Pension contributions, gift aid, allowable expenses, correct treatment of a foreign pension, an overlooked loss: all of them reduce the UK liability, and every reduction that produces an HMRC repayment reduces the foreign tax you actually bore.
The US consequence is that the credit claimed on the original return was overstated. You report the redetermination on Schedule C for the year the repayment occurs, and you amend the earlier US year, which will generally produce additional US tax and interest from the original due date. That interest charge is not a penalty and is not waivable on sympathy grounds; it is the price of having had the use of money that was not yours.
The planning point is timing. Where a UK repayment is foreseeable, it is frequently better to sequence the UK amendment before the US filing rather than after, so the correct credit goes in first time. That is a scheduling decision, and it is one of the reasons we run the two jurisdictions as one workstream in our US tax services and UK tax services engagements rather than as two sequential projects.
What happens if the UK tax goes up?
An additional UK liability, whether from a discovery assessment, a closed enquiry, or a voluntary disclosure, increases the foreign tax available for credit. That is usually good news, but only if it is claimed, and only if it is claimed within the applicable window.
Two traps recur. The first is that the additional UK tax may not be creditable in the year the client assumes, because of the paid-versus-accrued distinction above. The second is that additional UK tax frequently pushes the credit above the limitation for the year in question, so the incremental tax generates no immediate US benefit at all. Whether that stranded amount does anything useful is a separate analysis, and one that should be run before anyone assumes the UK payment has been neutralised on the US side.
The payment-window rule that catches late UK settlements
Where foreign tax is accrued and claimed but not actually paid within a defined period after the close of the year to which it relates, the Code treats it as refunded. It does not matter that you fully intend to pay, or that HMRC is content to wait, or that a time-to-pay arrangement is in place. The deemed refund happens by operation of law, it is a redetermination, and it must be reported.
For a UK filer this is a real exposure, not a theoretical one. Deferred balancing payments, disputed liabilities held over pending an enquiry, and instalment arrangements on a large capital gain all sit squarely in this territory. When the UK tax is eventually paid, it comes back into credit, but the interim reporting and the interim US liability are both real.
How this interacts with a streamlined filing
Streamlined submissions are especially exposed, for a structural reason. The procedure requires three years of amended or delinquent returns and six years of FBARs, all prepared at once, and the foreign tax credits across those years are frequently the largest numbers on the page. If the UK position for any of those years is subsequently corrected, the redetermination reaches back into a submission that has already been certified as non-wilful.
Handled properly, this is unremarkable: you notify, you amend, and the earlier certification is unaffected because the change reflects new information rather than an original misstatement. Handled badly, it looks like the numbers were never right, which is precisely the impression you cannot afford to give after a non-wilfulness certification. Our US UK tax accountants build the follow-through into the original engagement letter for this reason.
Penalties, interest, and what reasonable cause actually requires
Failure to notify the IRS of a redetermination carries a dedicated penalty, calculated as a percentage of the resulting deficiency and escalating for each month the failure continues, subject to an overall ceiling. It is separate from, and stacks on top of, ordinary accuracy-related exposure and interest on the underpayment.
A reasonable cause defence is available, but it is not a matter of asserting good intentions. It requires an affirmative written statement setting out all the facts relied on, made under penalties of perjury. In practice, the statements that succeed are the ones that document a real process: the date HMRC issued the revised calculation, the date the adviser was instructed, the reason for any delay, and the corrective filing made as soon as the facts were established. The statements that fail are the ones that say the client did not know.
On the UK side, the corresponding risk is different in kind. HMRC's penalty regime keys off behaviour and off whether a disclosure is prompted or unprompted. The consequence for cross-border filers is that the same underlying event, a corrected UK liability, is judged on process in the US and on candour in the UK. Both need managing, and they need managing together.
A worked sequence
Consider a US citizen resident in London who files a US return for 2024 in October 2025, crediting an estimated UK liability. In March 2026 the 2024/25 Self Assessment return is amended to claim relief that was originally missed, and HMRC repays a material sum in May 2026. The correct sequence is:
- Establish the revised UK liability by year, in sterling, with the HMRC calculation and repayment date evidenced.
- Identify which US years the reduced UK tax was credited against, and re-run the credit for each affected year.
- Prepare Schedule C (Form 1116) for the US 2026 return, the year in which the redetermination occurred, showing the original and revised foreign tax figures, the relation-back years, and the exchange rates applied.
- Prepare an amended US return for each earlier year whose liability changes, with a recomputed Form 1116.
- Calculate interest from the original due dates and settle it with the amendment rather than waiting for a notice.
- Diarise the notification deadline against the 2026 return due date, extensions included, because that is the date the penalty runs from.
Two currency points are easy to get wrong and expensive to correct. The original credit and the revised figure must be reported in the foreign currency with the applicable exchange rates identified, and a refund is generally translated at the rate applicable when the refund is received rather than at the rate originally used. A sterling repayment therefore does not automatically reverse a fixed dollar amount, and the difference is not an error to be smoothed over.
What good looks like
The firms that handle this well do three things. They decide the paid-versus-accrued question deliberately at the outset and document why. They keep a live schedule mapping every UK liability to the US year it was credited against, so that when a UK figure moves it is obvious in minutes which US years are affected. And they treat the UK amendment and the US notification as one instruction rather than two, so nothing is left to a client's judgement about whether an HMRC letter is worth forwarding.
For clients with UK trusts, UK pension arrangements, or multiple income sources across both systems, that mapping is not optional. It is the difference between a fifteen-minute update and a forensic reconstruction. We build and maintain it as standard for high net worth clients precisely because the reconstruction, done later and under a deadline, costs an order of magnitude more.
Speak to us before the numbers drift apart
If your UK liability has moved, is about to move, or is sitting under an open HMRC enquiry while a US return has already been filed, the position is fixable now and considerably harder to fix once a deadline has passed. We handle the UK amendment and the US notification as a single, evidenced workstream, with the interest computed and the reasonable cause file built before anyone needs it. To discuss your position in confidence, contact our cross-border team for a private consultation.
