Specialist US UK Tax Services: Filing Both Returns Late

A dual filer who has fallen behind needs the US and UK returns prepared as one connected engagement, not by two unconnected firms. The two systems use different tax years, different payment dates and different disclosure routes. Prepared separately, the filings routinely contradict each other and the foreign tax credit lands in the wrong year.

That single structural problem is why Specialist US UK tax services exist as a distinct discipline rather than as two domestic compliance services bolted together. At Jungle Tax we prepare both sides of a dual filer's compliance position from one reconciled dataset, and when a client is late on one or both sides we build the catch-up so that the US narrative and the UK narrative describe the same facts, in the same order, with the same numbers.

What actually goes wrong when the US and UK returns are prepared separately?

The failure is rarely a technical error inside either return. Taken in isolation, the UK Self Assessment is usually correct and the US Form 1040 is usually correct. The damage happens in the space between them, and it takes four recognisable forms.

• The credit lands in the wrong year. The UK adviser reports income for the year ended 5 April. The US preparer needs the tax paid during the calendar year. Nobody owns the translation, so the US return either over-claims a credit that has not yet been paid or under-claims one that has.
• The two disclosures tell different stories. A streamlined certification says the client did not understand a US filing obligation. A UK disclosure, drafted six weeks later by a different firm, says the client relied on their accountant. Both may be honest. Read together by a reviewing officer, they look rehearsed and inconsistent.
• Income is characterised differently on each side. An employer pension contribution, a share award, a partnership distribution or a property disposal is classified one way for HMRC and another way for the IRS, with no reconciling note explaining why the two figures differ. The difference is often correct. Unexplained, it reads as an error.
• Nobody holds the whole timeline. The client is late on the US side for six years and late on the UK side for two. Each firm fixes its own window. The overlap years are never reconciled and the resulting credit position is guesswork.

For a high-net-worth dual filer these are not cosmetic issues. They decide how much tax is actually paid, whether penalties are mitigated, and whether a catch-up filing is accepted quietly or opened for enquiry.

How do you reconcile a 6 April to 5 April UK tax year with a US calendar year?

The UK tax year runs 6 April to 5 April. The US tax year for an individual is the calendar year. Every UK tax year therefore straddles two US tax years, and every US tax year draws on two UK tax years. There is no election that makes this go away for an individual filer, so the reconciliation has to be built by hand.

The working method is to abandon the idea of converting one return into the other and instead build a single underlying ledger of income and tax events, each tagged with its actual date. From that ledger both returns are then generated. The ledger, not either return, becomes the source of truth.

The reconciliation ledger in practice

• Date every item, not just the period. Salary by pay date. Bonus by the date of constructive receipt. Dividends by payment date, not declaration date. Interest by credit date. Disposals by contract date for UK capital gains and by trade date for US purposes, noting where those diverge.
• Split UK PAYE by month. A P60 covering the year to 5 April is not directly usable on a US return. Monthly payslips, or an employer's payroll extract, let you allocate both gross pay and tax deducted to the correct calendar months.
• Convert at the right rate. Each item should be translated at the spot rate on its own date, or at an average rate applied consistently and disclosed. Mixing methods across years is one of the fastest ways to produce figures that cannot be reconciled later.
• Track the tax separately from the income. The income allocation and the tax-paid allocation are two different exercises. UK tax on year one income is frequently paid in a calendar year that also carries UK tax on year two income.

US versus UK: the structural differences that drive the mismatch

Feature	United States (IRS)	United Kingdom (HMRC)
Tax year	Calendar year, 1 January to 31 December	6 April to 5 April
Basis of liability	Citizenship and residence, worldwide income	Residence and, for some, the four-year FIG regime
Return deadline	Mid-April, with an automatic extension for filers abroad and a further extension available on request	31 October for paper, 31 January for online filing
How tax is settled	Withholding plus quarterly estimated payments	PAYE plus payments on account and a balancing payment
Double tax relief	Foreign tax credit on Form 1116, or exclusion of foreign earned income	Foreign Tax Credit Relief claimed on the foreign pages of the return
Late-filing catch-up route	Streamlined Filing Compliance Procedures, delinquent information return procedures, or amended returns	Digital Disclosure Service, Worldwide Disclosure Facility, or late returns with penalty mitigation
Offshore account reporting	FBAR and Form 8938, with separate thresholds and separate penalties	No standalone equivalent; foreign income and gains reported on the return
Assessment window	Generally three years, extended where income is substantially understated or certain forms are missing	Four, six or twenty years depending on the taxpayer's behaviour

Why does the date UK tax was paid decide which US year gets the credit?

This is the single most valuable thing a joint engagement gets right and two separate firms almost always get wrong.

Most individuals claim the US foreign tax credit on the cash basis. On that basis, foreign tax is creditable in the US year in which it is actually paid, not the year in which the underlying income arose. The IRS explains the mechanics in its guidance on the foreign tax credit for individuals. HMRC's own position on relieving doubly taxed income is set out in its guidance on tax on foreign income.

Now overlay the UK payment architecture. A UK Self Assessment liability is typically settled through two payments on account, due 31 January and 31 July, followed by a balancing payment the following 31 January. A single UK tax year is therefore usually paid across three separate dates spanning two calendar years, and any one calendar year will contain payments referable to two different UK tax years.

What that means for a filer who is behind

When a client is catching up, the distortion is severe. Someone who settles four years of UK liability in one lump sum in, say, March creates a single US calendar year carrying an enormous foreign tax payment, sitting against one year's worth of income. The credit limitation bites, a large excess credit is generated, and the earlier US years, which is where the income actually sat, may show tax due with no credit available.

Handled properly, that outcome is managed rather than accepted. The levers include:

• Sequencing the UK payments deliberately so that settlement falls in the calendar years where creditable capacity exists, rather than whenever the UK firm happens to finalise the figures.
• Considering the accrual election. An individual may elect to claim the credit in the year the foreign tax accrues rather than the year it is paid. It aligns the two systems far better, but it is made on a timely filed original return and, once made, binds all future years. For a client mid-way through a catch-up, that is a decision with a long tail and it must be modelled before it is made, not after.
• Using the carryback and carryforward. Excess credits can generally be carried back one year and forward ten, within the same category of income. Categorising correctly at the outset determines whether that relief is usable at all.
• Keeping the general and passive categories clean. UK employment income, UK dividends, UK interest and UK rental profits do not all sit in the same basket. A joint engagement allocates the UK tax between baskets on a defensible basis; a US-only preparer working from a single SA302 total usually cannot.

What evidence proves the date UK tax was actually paid?

A foreign tax credit claim is only as strong as the evidence behind it, and the evidence has to establish both the amount and the date. UK documents are not designed with that in mind, so the pack has to be assembled deliberately.

• SA302 tax calculation for each UK year, showing the computed liability.
• Tax year overview from the HMRC online account, which shows the liability and what has been paid against it.
• HMRC statement of account showing the actual payment dates, allocations and any interest charged. This is the document that carries the dates, and it is the one most often missing from a US file.
• Bank evidence of each payment leaving the client's account, matched line by line to the statement of account.
• P60 and P45 forms plus monthly payslips for PAYE deducted, since PAYE is paid across the year rather than in instalments.
• PAYE coding notices, which explain why deductions in a given month differ from the headline rate and prevent a reviewer treating the difference as unexplained.
• Repayment records, because a UK refund reduces the foreign tax paid and must be reflected in the US position for the correct year.

Where PAYE has over-collected and a refund follows, or where HMRC later amends a liability, the US credit already claimed is no longer accurate. US rules require a foreign tax redetermination to be reported when the foreign tax paid changes after the credit has been claimed. A firm running both sides sees the HMRC amendment as it happens and adjusts the US position in the same cycle. Two unconnected firms typically never learn of it, and the US return stays wrong.

If you are behind on both sides, which return should be prepared first?

Neither, in isolation. The correct answer is that the data is built first, the strategy is fixed second, and the returns are then filed in a deliberate order. Our working sequence for a dual filer in arrears is set out below, and it is the part of US UK tax accountant work that generalist firms most often skip.

• Step one: establish residence and status for every open year. UK residence under the statutory residence test, any split-year treatment, and US status including any period of non-residence. Everything downstream depends on this and it must be settled before a single figure is entered.
• Step two: build the full-period ledger. All income, all gains, all foreign accounts, all pension activity, dated and converted, covering the longest open window on either side rather than the shorter one.
• Step three: identify the disclosure route on each side. On the US side that usually means assessing eligibility for the IRS streamlined filing procedures, including the non-willful certification and the required years of returns and FBARs, as described in the IRS guidance on the Streamlined Filing Compliance Procedures. On the UK side it means choosing between a straightforward late return, a disclosure facility, or a formal disclosure with a considered behaviour analysis.
• Step four: draft both narratives together, before either is finalised. One factual chronology, written once, from which both the US certification and the UK disclosure are derived. They will use different language and different legal tests. They must not use different facts.
• Step five: model the credit position across all years. Run the US years with the UK payments allocated by actual date. Test the accrual election. Test the carryback. Identify which UK payments, if any, should be timed differently.
• Step six: settle the UK position in the modelled sequence, so that the payment dates support the credit outcome rather than undermining it.
• Step seven: file, then reconcile. Once both sides are lodged, produce a reconciliation schedule that explains every difference between the UK figure and the US figure for the same economic item. Keep it on file. If either authority asks, the answer already exists.
• Step eight: monitor for amendment. Any HMRC adjustment, refund or enquiry outcome is fed back into the US position immediately.

How can a US streamlined certification contradict a UK disclosure?

Both routes require the taxpayer to explain, in their own words, why the filings were not made. The tests are different. The US streamlined procedures turn on whether the conduct was non-willful. UK penalty mitigation turns on whether the behaviour was careless, deliberate, or neither, and on the quality of disclosure.

Because the tests differ, the temptation is to write two documents that each optimise for their own test. That is exactly the trap. Tax authorities exchange information, and a client's own signed statements are the most persuasive evidence available against them. The safe approach is a single chronology of facts, drafted once, from which each submission draws. Where the two authorities weigh those facts differently, that is a matter of legal analysis in each jurisdiction, not a matter of telling two stories.

Practical points that repeatedly cause contradictions:

• Dates of arrival and departure stated loosely in one document and precisely in the other.
• Account opening dates reported on FBARs that do not match the account histories disclosed to HMRC.
• Reliance on advisers asserted on one side and not mentioned on the other, when the same adviser was engaged throughout.
• Source of funds described one way for a UK disclosure and differently in a US narrative covering the same deposits.
• Amounts that differ because of exchange rates or timing, with no reconciling note, which reads as inconsistency rather than as translation.

Which assets behave differently on each side?

Cross-border return preparation for a wealthy dual filer is largely an exercise in handling items that the two systems treat incompatibly. The following recur in almost every catch-up file, and each one requires the two returns to be prepared together.

• ISAs. Tax-free in the UK, fully taxable in the US, and frequently holding non-US funds that trigger passive foreign investment company reporting with its own elections and its own deadlines.
• UK pensions. The treaty offers real protection, but the position on employer contributions, growth, lump sums and drawdown is nuanced and the interaction with the treaty's saving clause has to be worked through rather than assumed.
• UK unit trusts, OEICs and investment trusts. Ordinary UK retail investments that create significant US reporting obligations most UK advisers never mention.
• UK residential property. Different gain calculations, different rates, different rebasing, different treatment of mortgage exchange gains, and a UK reporting deadline that runs from completion rather than from the year end.
• Share awards and carried interest. Vesting, exercise and disposal are recognised at different moments in each system, and the sourcing of the income between the two countries drives the credit position.
• Trust interests. A structure that is efficient in the UK can be a US grantor trust with annual filing obligations attached. Our high-net-worth and private client work addresses this routinely.

What has changed for 2026 that dual filers should know?

Two shifts matter for anyone catching up now. First, the UK replaced the long-standing remittance basis for non-domiciled individuals with a residence-based regime for foreign income and gains from 6 April 2025, with transitional provisions for those previously taxed on the remittance basis. Any catch-up covering years either side of that change involves two different UK regimes within the same engagement, and the US treatment of the same income does not change at all, which alters the credit arithmetic across the transition. Our UK tax services team handles that boundary directly.

Second, the UK penalty regime for late filing continues to escalate steeply with time, with daily penalties and tax-geared penalties layered on top of the initial fixed penalty. HMRC sets out the current position in its guidance on Self Assessment penalties. Because unprompted disclosure attracts materially better treatment than prompted disclosure, the value of moving before HMRC or the IRS makes contact is measured in real money. The same principle applies on the US side, where streamlined relief is generally unavailable once the IRS has already initiated contact.

What does a properly reconciled engagement deliver?

At completion, a dual filer who came to us behind should hold six things: a complete set of filed US returns for the disclosure period; a complete set of UK returns or a formal disclosure for the corresponding period; the required FBARs and information returns; a reconciliation schedule tying every UK figure to its US counterpart; an evidence pack proving the amount and date of every foreign tax payment claimed; and a forward plan for payment timing so the credit position stays aligned in future years.

That last point is what turns a remediation into a permanent fix. Once the ledger exists and the payment calendar is deliberate, the annual cycle becomes routine. Our US tax services and UK teams then run both returns from the same file every year, and the mismatch never reopens.

Speak to us in confidence

If you are behind on one side or both, the position is almost always more recoverable than it feels, provided the two filings are built together and the disclosure is made before either authority makes contact. We work with founders, executives, investors and internationally mobile families whose affairs sit across both systems, and every engagement is handled under professional privilege and with complete discretion. To review your position, contact our cross-border team for a confidential, no-obligation consultation, and we will tell you plainly what the exposure is, what the route through looks like, and what it will cost.