US/UK Cross Border Tax Preparation Checklist: Every Document to Gather

A US/UK cross border tax preparation checklist has four parts: who you are and what you filed last year, what you earned in each country, what you hold in non-US accounts at its highest value, and where you were on each day of the year. Gather those for the US calendar year and for both UK tax years it touches. Most delays come from the last two parts, which no employer or bank sends automatically.

This checklist is for Americans in the UK, British nationals in the US and anyone else who files in both countries, whether you prepare your own returns or hand them to a firm. It lists each document, says which return uses it and flags the ones that have to be requested or built by hand.

Why is a cross border tax preparation checklist longer than a normal one?

Three reasons, and each adds documents that a single-country filer never needs.

The tax years overlap. The US taxes the calendar year and the UK taxes 6 April to 5 April. One US return draws on parts of two UK tax years, as our article on the UK tax year and the US tax year explains. A P60 covers one UK year, so it never matches a US year on its own.

The US wants balances as well as income. The IRS's comparison of Form 8938 and the FBAR says both report the maximum value of accounts or assets during the year. Bank statements show closing balances. The peak has to be found.

Residence is decided by days. Which country taxes what depends on where you were. Neither tax authority counts your days for you.

Part 1: identity, status and last year

Document or detail	Used for
Social Security number or ITIN for you, your spouse and each dependant	US return
UK Unique Taxpayer Reference (UTR) and National Insurance number	UK return
Citizenship, visa or green card status, and the date it began	Both
Last year's US return, with adjusted gross income and any carryovers	US return; e-filing identity check
Last year's UK return and SA302 tax calculation	UK return; payments on account
Last year's FBAR	Continuity of the account list
IRS identity protection PIN, if you were issued one	US e-filing
Bank details for refunds and payments in each country	Both

The US items in this table follow the IRS's own Gather your documents page, which lists Social Security numbers, bank account details, last year's adjusted gross income and any identity protection PIN. If you do not have last year's figures, the IRS provides transcripts through an Individual Online Account and HMRC provides an SA302 for the last four years.

Part 2: income documents

Employment

• P60 for each UK tax year that overlaps the US year. GOV.UK says you get a P60 if you are working for the employer at the end of the tax year.
• P45 if you left a UK job during the year.
• P11D if you received company benefits such as medical insurance or a car.
• Monthly payslips for the whole calendar year. These are what allow UK pay and UK tax to be re-cut from the UK tax year into January to December.
• Form W-2 from any US employer, and Form 1099-NEC for US contractor income.
• Details of share awards, options and bonuses: grant, vesting and sale dates and the values on each.

Savings and investments

• Bank and building society statements and annual interest summaries. GOV.UK's record-keeping guidance lists statements showing interest and income, dividend vouchers and unit trust tax vouchers.
• US Forms 1099-INT and 1099-DIV for US accounts.
• Annual tax packs from UK investment platforms, including ISAs. An ISA is ignored on the UK return and fully reportable on the US one.
• For every sale: what was sold, the dates and amounts of purchase and sale, and the currency.
• A list of every fund held outside a pension, with the fund name and identifier. UK funds can fall under the US passive foreign investment company rules, and the preparer needs the holdings to check.

Pensions

• Annual statements for each UK workplace pension and SIPP, showing your contributions, your employer's contributions and the year-end value.
• Statements for US plans: 401(k), IRA and Roth IRA, and Form 1099-R for any distribution.
• For pensions in payment: the P60 from the pension provider, State Pension details and Form SSA-1099 for US Social Security.

Property and self-employment

• Rental income and expenses by month, mortgage interest statements and letting agent statements.
• The purchase price, purchase date and cost of improvements for any let property. The US return claims depreciation, which needs these.
• Completion statements for any property bought or sold in the year.
• Business income and expense records, and records of estimated tax payments.

Part 3: what account information do you need for the FBAR and Form 8938?

This part is the one people leave until last and it takes the longest. For every financial account outside the United States you need the institution's name and address, the account number, the type of account and its maximum value during the year.

The IRS says the FBAR is required when the combined value of your foreign financial accounts exceeded $10,000 at any time during the calendar year. The test is cumulative, so several small accounts count together. Values are converted to US dollars using the end of the calendar year exchange rate.

Include:

• Current, savings and joint accounts.
• ISAs and investment platform accounts.
• Pension accounts, so that your preparer can decide how each is reported.
• Accounts you can sign on but do not own, such as an employer's account or a parent's.
• Accounts opened or closed during the year.

Form 8938 is a separate test with higher thresholds. The IRS comparison page gives them as follows.

Filer	Value on the last day of the tax year above	Or value at any time in the year above
Living abroad, unmarried or married filing separately	$200,000	$300,000
Living abroad, married filing jointly	$400,000	$600,000
Living in the US, unmarried or married filing separately	$50,000	$75,000
Living in the US, married filing jointly	$100,000	$150,000

You do not need to work out which form applies. Give your preparer the maximum and year-end value of every account and let them test the thresholds. Our comparison of the FBAR and Form 8938 explains the difference.

Part 4: days, moves and tax already paid

What travel records do you need for a US/UK tax return?

A dated list of every day spent in the UK, in the US and elsewhere, with flight times for the days you crossed a border. Two tests show why precision matters.

On the US side, the physical presence test for the foreign earned income exclusion needs 330 full days in a foreign country during any period of 12 consecutive months. The IRS defines a full day as 24 consecutive hours beginning and ending at midnight, so arrival and departure days usually do not count.

On the UK side, HMRC's Statutory Residence Test guidance says you are UK resident for the tax year if you spend 183 days or more in the UK in that year. Below 183 days the answer depends on further tests that look at your home, your work and your ties, and those need dates too.

Passport stamps are no longer reliable evidence. Use airline confirmations, a calendar and, if needed, card statements showing where you were spending.

Tax paid and payments made

• UK tax deducted under PAYE, from the P60 and payslips.
• Self Assessment payments, including payments on account made on 31 January and 31 July, with dates.
• US federal and state tax withheld, and estimated tax payments with dates.
• Tax withheld on dividends or interest by either country.

GOV.UK tells people with overseas income to keep proof of income earned abroad and proof of tax already paid, in the UK or abroad. Those two items are what make a foreign tax credit claim hold up in either direction.

Life events

Tell your preparer, with dates, about any of these: a move between countries, marriage or divorce, a child, a new job, a house purchase or sale, an inheritance or large gift, a pension withdrawal, a new company or a change in immigration status. Each one can add a form. If you are changing firms as well, our guide to switching US UK tax accountants lists the workpapers to request from the old one.

The currency question

Send documents in the currency they were issued in. Do not convert them yourself. The IRS says it has no official exchange rate and generally accepts any posted rate that is used consistently, and different items call for different rates: an average for regular income, the rate on the day for a one-off transaction, the year-end rate for account balances. A preparer needs the sterling figures and the dates to apply them. Our guide to the IRS exchange rate for pounds covers the choices.

When to gather each document

1. All year: keep a running log of travel days and save each payslip.
2. January: download December statements for every non-US account and note the year's highest balance while the online history is still available.
3. January to March: US Forms W-2 and 1099 arrive. Request annual statements from pension providers.
4. After 5 April: the UK tax year closes. P60s and platform tax packs follow over the next few weeks.
5. Before your US filing date: send the full set. If UK documents for the second UK tax year are not yet available, payslips and statements fill the gap.
6. After filing: store both returns, the FBAR confirmation and the supporting documents together.

Illustrative example: an American analyst in Manchester sends her preparer a P60 and a W-2 in March and assumes the job is done. The preparer comes back with eleven questions. Her P60 covers April 2025 to April 2026, so nine months of 2026 UK pay are missing until she finds her payslips. She has four UK accounts and a workplace pension; she knows the December balances but not the highest ones. She took three trips to the US and cannot say whether she was there for 34 days or 37. Each answer takes a week. The following year she keeps a travel log and downloads statements in January, and the same return takes one exchange of emails. This example is illustrative and does not describe a real client.

What people get wrong when gathering documents

Sending year-end balances only. The FBAR and Form 8938 ask for the maximum value.

Leaving out accounts with little in them. The $10,000 FBAR test is on the combined total. Once it is met, every account is listed.

Treating the ISA as invisible. It is tax-free in the UK only.

Converting everything to dollars first. It removes the information the preparer needs to choose the right rate.

Assuming one P60 covers the US year. It covers a UK tax year. The US year needs parts of two.

Throwing away purchase records. The cost of a house or a fund is needed in the year it is sold, which may be decades later. The IRS's record retention periods and GOV.UK's record-keeping rules are minimums.

Using the checklist

Work through the four parts in order and mark each line as sent, not applicable or still to come. A preparer can start with parts 1 and 2 and should not finish without parts 3 and 4. What happens to the documents next is set out in our guide to the US/UK cross-border tax preparation process.

US/UK Cross Border Tax — US CPAs and UK tax advisers working as one team; London, Manchester, New York, San Francisco. Our US/UK cross border tax preparation service uses one document request for both returns, and the same file feeds your UK Self Assessment return. To receive a checklist tailored to what you hold, get in touch.