US UK Tax Return Year-End Checklist for Americans in London

Before a single form is prepared, a dual filer in London must assemble one evidence pack: every foreign account with its peak balance, UK employment and investment documentation, dated proof of UK tax actually paid, and the entity paperwork that quietly triggers extra US information returns. This US UK tax return year-end checklist for Americans in London is the assembly stage, not planning.

At Jungle Tax we prepare US and UK returns side by side for founders, executives, fund principals and long-settled dual citizens across London. In our experience the difference between a clean filing season and a six-week scramble is almost never technical skill. It is whether the client arrived with the right documents, covering the right period, in a form that can be evidenced if either revenue authority asks. This guide is the document-assembly checklist we work from internally, written out in full.

Why document assembly, not planning, is the real year-end task

Most year-end content aimed at Americans abroad is planning content: harvest losses, top up a pension, time a disposal. That advice arrives too late for anyone already resident in the UK with a settled financial life, and it is not what a preparation engagement needs. What a preparer needs is source documents.

The reason is structural. A US federal return and a UK Self Assessment return describe the same financial life over two different periods, in two currencies, using two different definitions of almost everything. The US measures the calendar year to 31 December. The UK measures 6 April to 5 April. No single UK document you receive maps cleanly onto a US return, and no single US document maps cleanly onto a UK one. Every figure has to be rebuilt from underlying records, and rebuilding requires the records.

The second reason is defensive. FBAR and Form 8938 are information returns with penalties that attach to the failure to report, not to any tax underpayment. The evidence trail behind a reported peak balance matters as much as the number itself. Under the automatic exchange of information regime, UK financial institutions report accounts held by US persons directly to the IRS, so what you file is compared against what your bank reported. Discrepancies are visible.

What documents does a US UK dual filer need before preparation can begin?

We group the pack into six categories. Work through them in order; each one feeds the next.

• The account inventory - every foreign financial account, with peak and year-end balances.
• UK employment documentation - P60, P45, P11D, payslips, share scheme records.
• UK investment, property and pension documentation - consolidated tax vouchers, contract notes, ISA and GIA statements, pension valuations, rental accounts.
• Foreign tax paid evidence - dated to the correct period, distinguishing tax withheld from tax paid.
• Entity and holding paperwork - company, partnership and fund documents that trigger additional information returns.
• Currency and methodology notes - the conversion sources you used, recorded once and applied consistently.

The master account inventory

Build a single schedule listing every non-US financial account you held at any point in the calendar year, whether or not it produced income, whether or not it was open at 31 December, and whether or not you consider it yours in substance. Include current accounts, savings, cash ISAs, stocks and shares ISAs, general investment accounts, SIPPs and other pension arrangements, offshore bonds, spread-betting and brokerage accounts, digital-asset custodial accounts, business accounts over which you hold signature authority, and accounts held jointly with a non-US spouse.

For each line, record: institution name and address, account number, account type, whether your interest is direct or as a signatory only, the maximum value reached during the calendar year, the balance at 31 December, the currency, and the conversion rate applied. The IRS specifies that FBAR filers must retain records showing account holder name, account number, institution name and address, account type and maximum value, generally for five years from the FBAR due date. Build the schedule so it already satisfies that standard.

How do you evidence FBAR peak balances correctly?

The FBAR test is aggregate, not per account. If the combined maximum value of your foreign accounts exceeded 10,000 US dollars at any moment in the calendar year, every account is reportable - including the dormant one with 40 pounds in it. This catches almost every American living in London, because a single month's salary passing through a current account clears the threshold.

Three assembly errors recur:

• Using the year-end balance as the peak. The peak is the highest balance at any point. A London bonus paid in March and moved to a mortgage offset in April can produce a peak many multiples of the 31 December figure. Pull the full statement run, not the closing statement.
• Ignoring closed accounts. An account closed in July is still reportable for that calendar year. Download the final statements before the bank retires online access - most UK institutions purge closed-account history within a limited window, and reconstructing it later requires a written request.
• Double counting between linked accounts. If funds moved from a savings account to a brokerage account, both accounts report their own peak. That is correct and intentional; you may report an aggregate far above your actual wealth, and that is not a problem. What is a problem is netting them to look tidier.

For UK institutions that provide only twelve months of downloadable history, the practical answer is to download in January every year and keep a permanent local archive. The full technical statement of who must file and what must be retained is on the IRS FBAR page. If unfiled years are already behind you, our FBAR penalty calculator sets out the exposure ranges.

Form 8938: what additional evidence does FATCA reporting require?

Form 8938 overlaps with the FBAR but is not the same return, and the documents it needs go further. It reports specified foreign financial assets, which includes accounts but also stock in a foreign company held outside an account, interests in foreign partnerships, foreign-issued life insurance and annuity contracts with cash value, and interests in other non-US pooled vehicles. A private company shareholding held in certificated form is invisible to your bank statements and must be captured separately.

The thresholds for a US person whose tax home is abroad are substantially higher than for someone in the United States, which is one of the few structural advantages of the position. Form 8938 also asks for the maximum value during the year and requires you to identify where each asset is reported elsewhere on the return - so the schedule must cross-reference to your Schedule B, Schedule D, Form 8621 and Form 1116 entries. Assemble the valuation evidence with that cross-reference in mind. Filing thresholds and definitions are set out on the IRS Form 8938 page.

Where FBAR and Form 8938 documentation diverge

Assembly point	FBAR (FinCEN Form 114)	Form 8938 (FATCA)
Filed with	FinCEN, electronically, separate from the return	Attached to the Form 1040
Reporting period	Calendar year	Your US tax year
Threshold basis	Aggregate peak above 10,000 US dollars at any time	Higher thresholds, tested at year end and at peak
Signature-authority-only accounts	Reportable	Generally not reportable
Directly held foreign shares	Not reportable unless in an account	Reportable
Foreign pension interests	Generally reportable where an account exists	Reportable, with valuation evidence
Evidence to assemble	Statement run showing peak, institution details	Peak and year-end value, plus cross-reference to income reported

What UK employment documents does the US return actually need?

Your P60 summarises the UK tax year to 5 April. Your Form 1040 needs the calendar year to 31 December. A P60 therefore straddles two US returns and cannot be used as a W-2 substitute, however convenient that would be.

The document that solves this is the payslip run. Assemble all twelve monthly payslips (or 52 weekly) for the calendar year and total gross pay, PAYE income tax deducted, employee National Insurance, pension contributions and any benefits processed through payroll. Most London employers' payroll portals allow a bulk download; many purge access at termination, so extract them before any job change.

Also assemble:

• P60 for both overlapping UK tax years - the one ending in April of the calendar year and the one ending the following April - so the pro-ration can be reconciled and evidenced.
• P45 for any mid-year employment change, plus final settlement statements.
• P11D covering benefits in kind - private medical cover, car and fuel benefit, interest-free loans above the de minimis, relocation packages. These are UK-taxed benefits that also require US characterisation, and they are the single most commonly omitted document.
• Share scheme documentation - RSU vest statements showing vest date, quantity, fair market value at vest and shares withheld for tax; option exercise notices; ESPP purchase confirmations with the discount and the lookback price; and any records for tax-advantaged UK schemes such as EMI, CSOP, SAYE or a Share Incentive Plan. UK and US treatment of these diverge at the point of taxation, the measure of income and the sourcing, so the underlying grant and vest records - not the summary - are what preparation needs.
• Employer tax equalisation or protection calculations, hypothetical tax deductions, and any assignment letter, if you are on an inbound or outbound package.

What UK investment, pension and property records should you assemble?

Collect the consolidated tax certificate or annual tax voucher from every UK platform and broker, covering dividends, interest, equalisation payments and any accumulated income on accumulating funds. Then collect the underlying contract notes for every purchase and disposal in the year, because UK and US cost-basis rules differ: the UK pools shares of the same class under the section 104 regime and applies same-day and 30-day matching, while the US applies its own identification and wash-sale rules. A gain figure computed for HMRC cannot be lifted onto a Schedule D. The transaction-level records are mandatory.

Specifically assemble:

• ISA statements - cash and stocks and shares, with full holdings and transaction history. The ISA wrapper is invisible to the IRS: income and gains inside it are fully reportable, and the underlying funds are usually non-US collective investment vehicles.
• Fund holdings detail for every UK, Irish or Luxembourg-domiciled fund, ETF or investment trust, including ISIN, units held, purchase dates and prices, distributions received, and year-end value. These are the inputs for passive foreign investment company analysis and any Form 8621 that follows. If a fund holds UK reporting-fund status, capture the reporting-fund income statement too, because that is a UK requirement running in parallel.
• Pension documentation - annual statements for every workplace scheme, SIPP and defined benefit arrangement, showing opening and closing values, employer and employee contributions, and any transfers in or out. Defined benefit entitlements need the scheme's annual benefit statement. Where you rely on the US-UK treaty for deferral of growth, the file needs the scheme rules or provider confirmation of its character, not just a balance.
• Rental property records - a rent schedule, agent statements, mortgage interest certificates, service charge and ground rent demands, repair invoices split between capital and revenue, and, for a US return, the cost, improvement history and in-service date needed to compute depreciation. US depreciation on foreign residential property is mandatory, uses a longer recovery period than domestic property, and is recaptured on sale, so the acquisition file matters years before you sell.
• Offshore bonds and life policies - policy schedules, chargeable event certificates and surrender statements.
• Digital asset records - full transaction exports with acquisition dates, disposal proceeds and fees.

How do you evidence foreign tax paid and date it to the correct year?

This is where more foreign tax credit claims fail than anywhere else. The credit is claimed either on the paid basis or the accrued basis, and the choice governs which year's UK tax lands on which US return. A UK Self Assessment balancing payment made in January relates to a UK tax year that ended the previous 5 April, which itself straddled two US calendar years. Filing the claim without a documented allocation is guesswork.

Assemble, for the calendar year:

• PAYE income tax deducted per payslip, totalled for the calendar year, not the P60 figure.
• Your HMRC Self Assessment statement of account, showing balancing payments and payments on account, each with its actual payment date and the UK tax year it was allocated to.
• Bank evidence of each payment to HMRC, so the date is independently provable.
• Any HMRC calculation (SA302) and the filed return for the relevant UK years.
• Records of any refund received, because a refund of previously credited foreign tax is a redetermination event requiring notification.
• Withholding certificates or dividend vouchers showing tax withheld at source in third countries.

Keep the mirror-image file too. Where the UK is giving credit for US tax on US-source income, HMRC expects evidence of the foreign tax paid - the position set out in its helpsheet on relief for foreign tax paid (HS263). The two claims must be internally consistent: the same income cannot be treated as UK-source for one authority and US-source for the other.

Which entity and holding paperwork triggers additional information returns?

The returns in this category carry the largest penalties and are the most frequently missed, because the trigger is ownership or a role, not income. Run this list against your affairs and assemble the paperwork wherever the answer is yes.

• A UK limited company you own or direct. Even a modest consultancy vehicle or a personal service company can bring a US person within the controlled foreign corporation regime. Assemble the statutory accounts, trial balance, share register, incorporation documents, dividend vouchers, director's loan account movements and confirmation statement. A US information return for foreign corporations may follow, and it is prepared from a US-basis restatement of UK GAAP accounts - which takes weeks, not days.
• A partnership or LLP interest. Assemble the partnership accounts, your capital and current account statements and the allocation schedule.
• A foreign disregarded entity or UK branch operation. A single-member UK entity or an unincorporated branch of a US business is commonly treated as disregarded for US purposes and carries its own annual information return. Assemble the formation documents, the accounts on a US basis, and the functional currency and exchange records used to prepare them.
• Non-US funds. Almost every UK, Irish or Luxembourg-domiciled fund is a passive foreign investment company for US purposes. Assemble annual statements sufficient to compute either the mark-to-market or the default excess-distribution treatment, and any prior-year election records.
• A UK employer share plan or equity award. Options, restricted stock and share incentive awards granted by a UK employer need the grant, vesting and exercise records, the plan rules, and the amounts already taxed through UK payroll. Without them the US cost basis cannot be established and the same award is easily taxed twice.
• Transfers of property to a foreign corporation. Assemble the transfer documentation and valuations.

If any of these apply and prior years were filed without them, the correct route is usually a voluntary catch-up rather than a quiet amendment. Our IRS streamlined filing specialists handle these disclosures, including the Foreign Offshore Procedure for taxpayers resident outside the United States.

What currency conversion evidence should you keep?

Every figure on a US return must be in dollars, and every figure on a UK return in sterling. The IRS position is that you generally use the rate prevailing when you receive, pay or accrue the item, and that where multiple rates exist you use the one that most properly reflects income - guidance published on its foreign currency and exchange rates page. In practice a preparer will use transaction-date rates for discrete items such as a share disposal or a property sale, and an annual average for a stream of salary or rent.

Record, once per year, in a short methodology note: the rate source used, whether an average or spot rate was applied to each income category, and the specific rate used for FBAR maximum values. Consistency across years is more defensible than accuracy in any single year, and an undocumented change of method between years invites questions from both sides.

What if records are missing, or years were never filed?

Assembly frequently uncovers a compliance gap rather than a document gap - an ISA never reported, an FBAR never filed, a UK company never disclosed, or a run of years missed entirely by someone who did not realise that US citizenship carries a filing obligation regardless of residence. Accidental Americans born in the United States to British parents, and long-term residents who assumed UK tax paid was the end of the matter, are the two profiles we see most often in London.

Do not begin by filing the current year in isolation. A current-year return filed correctly while prior years sit wrong can foreclose the more favourable catch-up routes. The sequence is: establish the number of open years, reconstruct the account inventory across that whole period, quantify the exposure, and then choose the disclosure route. Where records genuinely cannot be reconstructed, banks and platforms will produce historic statements on written request, and reasonable estimation supported by a documented methodology is accepted in some contexts - but that judgment belongs with your adviser, not your spreadsheet.

How long must the records be kept once the returns are filed?

Two retention clocks run in parallel. On the US side, FBAR supporting records are generally kept for five years from the return's due date, and the basis records behind a property, a share holding or a pension run for as long as you hold the asset plus the assessment period after disposal. On the UK side, HMRC requires records to be kept until at least the end of a defined window after the filing deadline, with a longer period where you are self-employed or a landlord; the general framework is set out in the GOV.UK guidance on Self Assessment record keeping. Where a claim, election or carryforward is involved - a foreign tax credit carryover, a pension basis, a PFIC election - keep the file indefinitely. Carryovers are only as good as the evidence supporting the year they arose.

A working timetable for the London dual filer

The dates below are the assembly milestones, not the filing deadlines, and they assume the calendar-year US return and the UK Self Assessment for the tax year ending the following April.

Period	US side assembly	UK side assembly
Early January	Download all 31 December statements and full-year statement runs before institutions purge history	Extract December payslip and year-to-date figures
January to February	Complete the account inventory with peak and year-end values; note conversion sources	Confirm the prior UK year's Self Assessment is filed and the statement of account is downloaded
February to March	Assemble broker consolidated vouchers, contract notes, fund holdings for PFIC analysis	Assemble rental accounts and agent statements
April	Deliver the pack to your preparer ahead of the standard filing deadline	Collect the P60 for the UK year just ended; capture the 5 April holdings position
May to July	Finalise the return under the automatic extension available to filers abroad	Collect the P11D covering benefits in kind
Autumn	Complete any extended filing and confirm the FBAR is submitted	Prepare and file Self Assessment; reconcile foreign tax credit positions both ways

The single most valuable habit is the January download. Almost every painful reconstruction we are asked to perform traces back to an account closed, a job left or a platform migrated, with the underlying history no longer available. Documents are cheap to keep and expensive to recover.

Assembling the pack with a preparer who files both returns

A checklist only works if the person receiving it prepares both sides. A US preparer who never sees the Self Assessment cannot verify that foreign tax credits match the tax actually paid; a UK accountant who never sees the Form 1040 cannot check that the same income is not being sourced two different ways. The interaction is where the money is, and it is where generalist advice consistently falls short. Further reading across our cross-border guides and our overview of working with US UK tax accountants sets out how the two filings are reconciled in practice.

If you are assembling this year's pack and want it reviewed before preparation begins - or if the assembly has surfaced accounts, entities or years that were never reported - contact our cross-border team for a confidential consultation. We will tell you precisely which documents are missing, what the exposure looks like, and the order in which to put it right.