Tax help when you're moving between the US and the UK

Your situation

A job offer, a relationship, a return home — and suddenly a date on which everything about your tax life will change. Movers in both directions share the same problem: two tax systems briefly overlapping, one set of assets built entirely under the old system, and a short pre-move window in which choices are still cheap.

What each country will expect from you

Moving to the UK: residence is determined by the statutory residence test, and the arrival year can often be split between non-resident and resident periods. Once resident you are within Self Assessment for anything untaxed at source — register by 5 October after the tax year, file online by 31 January. Qualifying new arrivals may claim the four-year foreign income and gains regime that replaced the remittance basis from 6 April 2025. If you are American, your US filing obligations continue unchanged alongside all of this.

Moving to the US: the substantial presence test can make you a US resident taxpayer — on worldwide income — earlier than you expect, and everything you leave in the UK becomes "foreign" to your new tax home: ISAs lose their shelter in US eyes, UK funds can fall into the punitive PFIC regime, and UK accounts start counting towards the $10,000 FBAR trigger.

In both directions, the country you leave keeps a claim on some of what you built there. US retirement accounts stay within the US system and are eventually drawn under treaty rules; UK pensions acquire US reporting the day their owner becomes a US person; and a home left behind and later let or sold generates filings in both countries for years after the move itself.

The classic traps

• Selling on the wrong side of the residence line. The same disposal can be tax-free or heavily taxed depending on which week it happens.
• Arriving with the wrong portfolio. Funds that were ideal at home can be toxic to the destination country — PFICs for arrivals to the US, non-reporting funds for arrivals to the UK.
• Straddled income. Bonuses, vesting equity and deferred pay that span the move can be claimed by both countries; the treaty and careful sourcing sort it out, but only if someone is watching.
• Forgetting the country you left. US states can cling to former residents, and UK duties can continue for departures — leaving cleanly is a filing exercise, not just a flight.
• Departure paperwork on autopilot. Payroll instructions, withholding certificates and residence notifications in the old country rarely update themselves; stale withholding is usually recoverable, but slowly and through extra filings.

One firm, both returns

A move is the one moment when you genuinely need both countries' rules applied to the same facts at the same time. We prepare US returns and UK Self Assessment under one roof, so the departure-year and arrival-year filings tell one consistent story — residence dates, split years, credits and elections all aligned. Fixed fees are agreed before work begins.

When to get advice

Ideally three to six months before you move, while sales, contributions and account changes are still options rather than regrets. If the move has already happened, the arrival-year returns still hold most of the remaining levers. Either way, a consultation before the first post-move filing is the single highest-value hour of the whole process.