US/UK Tax Planning Before You Move: The 90-Day Pre-Departure Checklist

Pre-move tax planning between the US and the UK is the work you do in the ninety days before the move, when residence dates, asset sales and account structures are still choices rather than facts to be reported. The same sale of a fund, the same pension contribution, the same house completion can be tax-free or taxable depending on which side of the move date it falls. Once you have landed, the options narrow to compliance.

This checklist is organised by time: what to settle three months out, one month out and in the final week, for both directions of travel. It draws on our guides to the Statutory Residence Test, split year treatment and the moving abroad tax checklist, and on our cross-border tax planning service, which runs this process for clients moving either way.

Why does the timing of a US/UK move matter so much for tax?

Because both countries decide residence by dates and day counts, and residence decides what is taxed. GOV.UK's guidance for people coming to the UK is blunt: you pay UK tax on income if you come to live, work or study here, and whether foreign income is taxed depends on whether you are resident. The IRS's substantial presence test makes a Brit a US tax resident after 183 weighted days, and US citizens are taxed wherever they live. Layer on the UK's 6 April tax year against the US calendar year, and a move in, say, early March produces a different pattern of liabilities from a move in late April. The planning window is before the date is fixed.

Ninety days out: fix the timeline and the big decisions

1. Choose the move date deliberately. Check which UK split-year case you will meet (Case 1 to 3 leaving, Case 4 to 8 arriving) and how the date affects the US year. A Brit arriving in the US in the second half of the year may stay a US non-resident for that year; an American leaving the UK needs to be non-resident the following UK year for the departure cases to work.
2. Map every asset and account on both sides: bank accounts, ISAs, SIPPs and workplace pensions, 401(k)s and IRAs, brokerage accounts, property, company shares, crypto. Note the owner, the country, the current value and the original cost.
3. Investments: decide what to sell and what to restructure. A Brit moving to the US faces two problems on arrival: the US taxes gains from original cost, not from the value on arrival, and UK funds become PFICs. Realising gains while still UK resident, within the UK's capital gains annual exempt amount and rates, and switching to US-compliant holdings is often the largest saving in the whole move. Our guides to investing as an American in the UK and US ETFs for UK residents cover the mirror problems for Americans heading east.
4. Pensions. Decide whether to roll a 401(k) into an IRA while you still have a US address (custodians are reluctant afterwards), whether to make final UK pension contributions while UK relief is available, and how a SIPP will be disclosed on Form 8833 once you are US resident. See 401(k)s for UK residents and SIPPs on a US return.
5. Property. If you will sell a main home, check both reliefs before exchange: the US Section 121 exclusion of $250,000 ($500,000 for a couple) against UK private residence relief, and the Section 988 currency gain on repaying a sterling mortgage, which catches Americans who did nothing but pay off their loan. If you will let the property, understand the non-resident landlord rules on the UK side and Schedule E depreciation on the US side.
6. Business interests. A UK limited company owned by a new US resident becomes a controlled foreign corporation with Form 5471 and possible GILTI; a US LLC owned by a new UK resident is opaque to HMRC and transparent to the IRS. Both can be restructured before the move far more cheaply than after. See founder tax for a US/UK startup.

Thirty days out: the exits and the elections

Moving from the US to the UK	Moving from the UK to the US
Break state residency: new licence, voter registration and address outside the state; close state-linked accounts; keep dated evidence. California, New York and Virginia are the hardest to leave.	Decide whether to use the UK's departure rules: tell HMRC via form P85 or the SA109 pages, and check that UK-source income such as rent will be reported as a non-resident (GOV.UK's guidance on UK income if you live abroad).
Decide, with numbers, whether to claim the UK's four-year Foreign Income and Gains regime. For a US citizen it can simply shift tax to the IRS while costing the personal allowance; see our FIG regime guide.	Decide whether to accelerate UK income (bonus, dividends) into the UK year, or defer US income until after arrival, depending on which country's rate is lower for that item.
Do not open an ISA holding UK funds; set up US-compliant investing instead.	Sell or restructure UK funds and ISAs that would become PFICs on arrival; realise gains within the UK exempt amount.
Make a final IRA or 401(k) decision and set W-8/W-9 status with US custodians.	Make final UK pension contributions while relief is available; obtain a state pension forecast.
List every non-US account for the FBAR and Form 8938 you will file from now on (thresholds).	Open a US bank account and brokerage early; many UK platforms will close accounts for US residents.

The final week: record everything

The move date is the reference point for most of the calculations that follow, so the last week is about evidence.

• Statements showing every account balance on the move date, in local currency.
• Valuations of property, investments and company shares on that date, with the source.
• The exchange rate on the date, from a published source you will use consistently.
• Travel documents proving the date itself, and the lease, completion or employment start date at the destination.
• A note of where your home, family and possessions were on either side of the date; the UK's accommodation and family ties and the US domicile tests both look at facts, not intentions.

Our guide to handling the UK and US tax year mismatch explains how those records flow into both returns in the first year.

What a well-planned move looks like in practice

Illustrative example: a British software engineer accepts a role in Austin starting 1 September 2026. Ninety days out she maps a stocks and shares ISA with £40,000 of gains across four UK funds, a workplace pension and a flat in Leeds. In June she sells the funds, using her UK capital gains exempt amount and paying UK tax at UK rates on the rest, so the US will never tax that history or treat the funds as PFICs. In July she makes a final pension contribution and obtains a state pension forecast. In August she lets the flat, registers under the non-resident landlord scheme and opens a US brokerage account. She moves on 1 September, keeps statements from that day, files a UK split-year return for 2026/27 and a US Form 1040-NR for 2026 because she is under the substantial presence threshold, then a full Form 1040 from 2027 with the Leeds rent on Schedule E and the pension disclosed on Form 8833. Texas has no state income tax. This is illustrative only; the right sequence depends on the actual assets and dates.

What should Americans moving to the UK do differently from Brits moving to the US?

The checklist is the same shape in both directions but the emphasis flips. For an American heading to Britain, citizenship means the US return never stops, so the planning is about not creating UK structures the US punishes: no UK funds inside an ISA, no UK pension contributions beyond what the treaty protects without a Form 8833 plan, and an honest look at whether the UK's four-year FIG regime does anything other than hand tax to the IRS. The state exit is the one genuinely American task, and the one most often skipped. For a Brit heading to America, the US return starts from the first day of residence and reaches back to original cost, so the planning is about cleaning the slate before arrival: realising gains, exiting UK funds, deciding what to do with the pension, and choosing an arrival date that keeps the first US year a non-resident one if the numbers favour it. HMRC, meanwhile, needs to be told you have gone and will keep taxing UK rent and some UK pensions as a non-resident.

The common thread is that the higher-tax country sets the floor and the lower-tax country credits it, so moving assets and income across the date is only worth doing where the two countries treat the item differently. Our guides for Americans in the UK and Brits in the US list those items side by side.

The mistakes we see most often

• Moving first and asking afterwards, when the ISA is already a PFIC and the gains already belong to the US.
• Leaving California or New York without breaking residency and paying state tax on a London salary.
• Treating the UK's FIG regime as free money without modelling the US side.
• Selling the main home a month after the move instead of a month before, and losing one country's relief.
• Not recording move-date balances and values, then reconstructing them years later for an audit.

The bottom line

Three months is enough time to choose the date, clean up the investments, decide on pensions and property, exit the state or tell HMRC, and record the position on the day you go. It is not enough time if the house is already under offer and the contract already signed. Our moving abroad service runs this checklist for clients moving in either direction, from London and Manchester to New York and San Francisco, with US CPAs and UK tax advisers working as one team. The earlier you talk to us, the more of the move is still a choice.