Offshore Disclosure When UK and US Years Do Not Match

Offshore disclosure across two tax authorities rarely covers the same years twice. A Streamlined Foreign Offshore pack reconstructs six years of records — three US tax years plus six FBAR years — while HMRC's assessable span is set by behaviour and may be four, six, twelve or twenty. The real decision is which UK years to put in front of HMRC.

That decision is almost never addressed in published guidance. UK disclosure pages explain HMRC's time limits. US pages explain the streamlined programme. Neither explains what to do when the two spans are different lengths, start in different months, and are driven by entirely unrelated logic — which is the ordinary situation for an American in London, or a Briton who has returned home with a US filing history behind them. This guide is about that single problem: choosing the UK span when the US span is already fixed, deciding whether to volunteer years HMRC can no longer assess, and keeping two disclosures consistent when they deliberately cover different periods.

Why the two spans are set by completely different machinery

The US programme is a template. Under the Streamlined Foreign Offshore Procedures, an eligible taxpayer files delinquent or amended returns for each of the most recent three years for which the return due date has passed, and delinquent FBARs for each of the most recent six years for which the FBAR due date has passed. Nothing about the taxpayer's conduct changes those numbers. Non-willfulness is a gate to eligibility, not a dial that lengthens or shortens the pack. Every submission, whether the underlying facts are mild or genuinely messy, reaches back across the same six calendar years of financial records.

HMRC works the other way round. The number of years is an output of behaviour, not an input. Where a taxpayer registered for Self Assessment by the appropriate deadline and took reasonable care, HMRC's published disclosure guidance points to a maximum of four years. Careless behaviour, with timely registration, points to six. Where the inaccuracy involves an offshore matter, the reach extends up to twelve years. Deliberate conduct — and a failure to notify chargeability at all — points to twenty. Crucially, HMRC's own guide to making a disclosure puts that classification on the taxpayer: you decide whether the error arose despite reasonable care, through carelessness, or deliberately, and the number of years follows from your answer.

So two disclosures built by the same adviser, from the same bank statements, for the same client, will cover different sets of years — and in neither case is the number a matter of preference. One is fixed by programme design. The other is fixed by an honest behavioural analysis you have to be able to defend.

US versus UK: what actually fixes the number of years?

Question	United States (Streamlined Foreign Offshore)	United Kingdom (voluntary disclosure)
What sets the span?	Programme terms: three tax years of returns, six years of FBARs	Behaviour: broadly four, six, twelve or twenty years
Who decides?	The IRS, in advance, for everyone	The taxpayer self-assesses; HMRC may disagree
Does conduct change the span?	No — non-willfulness is an eligibility condition only	Yes — it is the entire determinant
Year end	31 December	5 April
What is actually filed	Three returns, six FBARs, a signed non-willful certification	One disclosure covering the chosen years: tax, interest and penalties computed year by year
Can the span be varied for one income source?	No — it is client-wide	Yes — behaviour can differ source by source, so the span can be ragged
Consequence of getting it wrong	Submission may be treated as outside the programme	Years left open, and mitigation for disclosure quality reduced

The years themselves do not even line up

Before comparing spans, note that the two calendars are offset by nearly three months. A US tax year ends on 31 December; a UK tax year ends on 5 April. Every UK year therefore straddles two US years, and every US year straddles two UK years.

The practical effect is larger than it sounds. A streamlined pack covering the 2022, 2023 and 2024 US years touches parts of five UK tax years. A six-year FBAR span touches parts of seven. So a UK year you have decided sits outside HMRC's assessable window can still be half-covered by an FBAR you are about to file, and by account balances the IRS will hold. Interest, dividends and distributions have to be apportioned by payment date, never by year label — and any schedule that maps "2022" to "2022/23" without dates will produce two sets of figures that do not reconcile.

The four overlap shapes you will actually meet

In practice the span mismatch resolves into one of four patterns, and the right answer differs in each.

• UK window shorter than the US pack. The client registered for Self Assessment on time, filed UK returns, and took reasonable care over UK-source income — but never filed in the US. The UK reach may be four years while the FBAR span is six. The oldest years of the US pack correspond to UK years HMRC can no longer assess at all. This is the most common shape for professionally advised UK residents who simply never engaged with their US citizenship.
• UK window longer than the US pack. The client never notified chargeability to HMRC, or the offshore matter falls into the extended offshore reach. The UK disclosure may run to twelve or twenty years while the US pack still stops at six. Here the US filing is a subset of the UK one, and consistency runs in a single direction: everything in the US pack must appear in the UK disclosure, but not the reverse.
• Roughly equal spans. Careless behaviour with timely registration gives six UK years against six FBAR years. Superficially the cleanest case — but the calendar offset still leaves ragged edges at both ends, and the three filed US returns still cover only half the UK period.
• Ragged, source by source. The most realistic and least written-about shape. Behaviour is rarely uniform across a wealthy client's affairs: UK employment income reported correctly, an offshore deposit account overlooked carelessly, a foreign pension nobody thought was reportable, a distribution never notified at all. Each source can carry its own behaviour and therefore its own span, inside one disclosure. The US pack, by contrast, treats every source identically.

Identifying which shape you are in is the first substantive step, and it has to be done before any figure is computed. Our IRS streamlined filing team and UK disclosure team work the span question jointly for exactly this reason.

Should you offer HMRC years it can no longer assess?

This is the question that decides the shape of the whole engagement, and it deserves a direct answer: sometimes, and never by default.

The starting point is that HMRC cannot assess a year that falls outside the applicable limit for the behaviour disclosed. But there is no rule stopping a taxpayer from putting information — or money — forward voluntarily, and settlements can and do include amounts a taxpayer offers for periods that could not be assessed. So the choice is genuinely open, and it is a judgement call rather than a compliance requirement.

When volunteering out-of-span years helps

• The US pack already documents them in full. If FBARs are going to the IRS for six years, the marginal cost of describing those same years to HMRC is close to zero — and silence about years you have plainly reconstructed elsewhere can look selective rather than time-barred.
• The narrative requires them. An account opened seven years ago whose balance only makes sense with its earlier history; an income source that began outside the span and continued inside it. Truncating the story at the assessing limit can make the in-span figures look inexplicable.
• You are seeking full credit for disclosure quality. HMRC's penalty mitigation turns on telling, helping and giving access. A demonstrably complete picture supports the top of the reduction range in a way a minimal one does not.
• The out-of-span figures produce little or no UK tax. Where earlier years fall within allowances or were taxed at source, you are volunteering information rather than money — cheap completeness.

When volunteering out-of-span years harms

• It can recharacterise the behaviour. This is the serious one. Volunteering a longer history is, in substance, evidence that the omission ran longer and started earlier. Handled clumsily, an offer intended to look cooperative can support a conclusion of deliberate conduct — which does not close four years, it opens twenty.
• The earlier years cannot be evidenced to the same standard. Banks purge records; portfolios change custodian. A half-supported figure for an out-of-span year invites scrutiny of the well-supported ones.
• It confuses a year-by-year analysis. Penalties are computed year by year on the behaviour for that year. Adding years computed on a different, looser basis muddies the schedule HMRC will actually work from.
• It creates an unanswerable question. If you offer a year, you must be able to explain how you arrived at the number. "We estimated it to be helpful" is not a position you want on the record.

The middle path: disclose the facts, not necessarily the tax

In most span-mismatch cases the right answer is neither silence nor a full computation. The disclosure narrative describes when each account was opened, when each income source began, and what the position was before the assessable period — while the computation is confined to the years properly in scope. The story is complete; the numbers are bounded.

What makes this work is saying so explicitly. A single sentence in the covering narrative — identifying which years are computed, which are described only, and why — converts what could look like an omission into a stated, defensible position. Leaving the reader to notice the gap for themselves is what turns a technical judgement into a credibility problem.

How to decide which UK years go into the disclosure

1. Fix the US span first. It is mechanical and not open to argument: three tax years, six FBAR years, counted from the most recent due dates that have passed. Confirm the counts against the IRS guidance for US taxpayers residing outside the United States.
2. Map every source to the years it existed — in both calendars, by date, not by label.
3. Assess behaviour per source, per year. One behaviour conclusion for the whole client is almost always wrong for a complex estate.
4. Take the longest span any single source requires. That sets the outer edge of the UK disclosure.
5. Test the out-of-span years for US exposure. Which of them are already documented by an FBAR, an account opening date, a foreign asset schedule or a pension history in the US pack?
6. Decide, for each exposed year, between full computation, narrative-only, or nothing — and write down the reason at the time.
7. Reconcile against the US certification. No year in the UK disclosure should contradict anything asserted in the US narrative.
8. Keep a span memorandum on file. If either authority asks why a year is absent, the answer should already exist on paper, dated.

Keeping two disclosures consistent when they cover different periods

"Non-willful" is not the same as "reasonable care"

The single most damaging inconsistency we see is vocabulary. The US certification requires the taxpayer to state that the failure resulted from non-willful conduct — negligence, inadvertence, mistake, or a good-faith misunderstanding of the law. That description sits perfectly comfortably alongside HMRC's careless. It does not automatically mean reasonable care was taken.

A narrative drafted to sound maximally innocent for the IRS, which asserts the taxpayer did everything a reasonable person would do, filed alongside a UK disclosure computed on a careless six-year basis, is a documented contradiction between two filings held by authorities that exchange information about the same accounts. The discipline is to write one factual account of what happened and derive both filings from it — never to draft each to its own audience.

Figures that must reconcile even outside the overlap

Account opening and closing dates. Peak balances. Income by source and by date. Currency conversion method. These appear in both submissions regardless of which years are computed for tax. An FBAR filed for a year excluded from the UK disclosure still exists, is still readable, and still states a maximum balance.

Currency deserves particular care. US filings and UK filings use different conversion conventions, so the same underlying interest will convert to two different figures. Document the method used on each side so that a discrepancy reads as arithmetic rather than as a second version of events.

Where the earlier US years surface anyway

It is tempting to think the US pack only "says" three years, because only three returns are filed. It does not. The six FBAR years stand on their own. The certification narrative addresses the history of the non-compliance rather than a three-year window. Cost basis, carried-forward items, holdings acquired before the covered period and long-standing pension arrangements all carry their history into the filed returns. Any assessment of which UK years are genuinely exposed has to be made against the whole pack, not against the three returns.

Sequencing: which disclosure goes first?

There is no ordering rule, but there are practical constraints. The facts should be fixed — accounts identified, balances reconstructed, behaviour analysed — before either submission is finalised, because each one commits you to a version of events. Notifying HMRC starts a clock: under the digital disclosure route you are expected to submit the disclosure and pay within a defined window after receiving your disclosure reference, which is not enough time to run a full six-year US reconstruction from a standing start.

In most engagements that means the reconstruction work is done once, jointly, and the notification to HMRC is timed so the UK computation can be delivered inside the window while the US pack is finalised in parallel. Where a nudge letter or an IRS contact has already arrived, that sequencing becomes considerably tighter — and eligibility for the US programme itself may be affected.

A worked example of the mismatch

A US citizen, UK resident in London since 2011, registered for Self Assessment on arrival and has filed UK returns on time every year. UK employment income and a UK investment portfolio have always been reported correctly. Two offshore deposit accounts have produced modest interest — never included on the UK returns. No US returns have been filed since 2016.

The US span is fixed: three years of returns, six years of FBARs, a signed certification. Six calendar years of records must be reconstructed.

The UK span is not. The client registered on time and took reasonable care over the UK sources, so those sit at the shorter end. The offshore interest is a different question: if the omission was careless, the reach is six years; if the facts place it in the extended offshore category, it is longer. The UK disclosure is therefore ragged — a short span for the UK sources, a longer one for the offshore interest, inside one submission.

Now vary the facts. Had the client never registered for Self Assessment at all, the failure-to-notify analysis would extend the UK reach dramatically, and the six-year US pack would become the shorter of the two documents. Same client, same accounts, opposite mismatch — and an entirely different answer to what goes in front of HMRC.

The mistakes we see most often

• Assuming the UK number must equal the US number, and disclosing six UK years because the FBARs cover six.
• Treating the US non-willful certification as the UK behaviour conclusion.
• Mapping years by label rather than by date, and producing schedules that cannot reconcile.
• Disclosing to HMRC only the years the US pack happens to cover — which is an arbitrary boundary with no UK basis.
• Volunteering twenty years of figures "to be safe", and inadvertently supplying the evidence for a longer assessing period.
• Filing the UK disclosure before the behaviour analysis is finished because the notification clock is running.
• Never recording, at the time, why a particular year was left out.

None of these is a computational error. They are all decisions taken without recognising that a decision was being made — which is precisely what a span mismatch does to an otherwise careful catch-up.

Getting the span decision right

Jungle Tax prepares US and UK catch-up filings for internationally mobile individuals and families whose affairs sit on both sides of the Atlantic. We build the US streamlined pack and the UK disclosure from a single reconstructed evidence file, decide the span question deliberately and document it, and make sure two submissions written for two authorities tell one consistent story. You can read more about our approach to US-UK cross-border compliance and our work with high-net-worth clients, or browse our full library of cross-border guides.

If you are preparing a streamlined submission and are unsure how many UK years belong in front of HMRC — or whether to offer years HMRC can no longer assess — contact our cross-border team for a confidential consultation. The span decision is far easier to take before either disclosure is filed than to defend afterwards.