One form tells HMRC you have gone. The rest of the year is the work.

The form that tells HMRC you have left the country. It records your departure date and your expected income afterwards. HMRC uses it to review your tax code and to repay tax over-deducted through PAYE.

Not always, though filing it is usually sensible. HMRC's publication on leaving the UK and getting your tax right explains the form and who needs it. You can skip it where you already complete a Self Assessment return, because the return does the same job.

You do not need it where you already complete a Self Assessment return, because the return does the same job.

Where PAYE was your only exposure, the form is how a refund reaches you. Leaving in June often means a whole year's allowances against three months of pay.

Possibly, and more often than people expect. A return is due for the departure year where you have untaxed income, capital gains to report, or a continuing UK source such as rent.

Registration deadlines apply, and they do not pause because you have moved.

Our guide to registering for Self Assessment covers the timing and the penalties for missing it.

UK sources, broadly. GOV.UK's guidance on tax on UK income if you live abroad sets out what stays in charge once you are non-resident. Rent from a British property is the common one, and certain pensions and some investment income can also remain.

Rent from a British property is the common one. Certain pensions and some investment income can also stay within the British net.

Bank interest and dividends are treated differently from rent, so the picture is not uniform.

So leaving does not close your British file. It narrows it.

Under the statutory residence test, which has specific rules for years of departure. HMRC's guidance note on the test sets them out. Where they apply, the year divides into a resident part and a non-resident part, and Britain taxes worldwide income only for the first of those.

That treatment is mechanical rather than optional. It depends on why you left and what you did afterwards.

Our guide to the statutory residence test works through the conditions.

Getting the split right is the difference between reporting a whole year of American income to Britain and reporting none of it.

It follows its own rules once you work abroad, separate from income tax. GOV.UK's guidance on National Insurance if you work abroad explains when contributions continue and when they stop.

Voluntary contributions are also possible, and they protect your state pension record.

Whether that is worth doing depends on how many years you already hold and what you expect to need.

For an American, the social security agreement then decides which system collects on your new earnings.

Not in structure, only in content. You still report the whole calendar year wherever you lived during it, so the move does not split the American filing the way it can split the British one. What changes is which relief you can claim for that year.

What changes is the relief you claim. Leaving Britain part way through a year can end your qualification for the foreign earned income exclusion for that year, depending on the test you were using.

The foreign tax credit continues to work on UK tax you actually paid.

Our comparison of the exclusion and the credit explains which survives a mid-year move.

Your employer operates the code until you leave, then issues a P45. That document shows pay and tax to the date of leaving, and it is the single most useful piece of paper in the whole exercise.

Keep it. Both HMRC and your American return will rely on those figures.

Where a bonus or share award arrives after departure, the payroll may deduct at a rate that assumes you are still here.

That is recoverable, and it takes months. Telling payroll your leaving date in advance prevents most of it.

Closing accounts feels tidy and is not always wise. A UK account remains useful for rent, refunds and pension correspondence, and closing it can complicate a repayment from HMRC.

ISAs are the exception worth thinking about. You cannot keep subscribing once you are non-resident, and an American never had the US tax benefit anyway.

Whatever you keep, the balances still count towards your American reporting thresholds.

Our comparison of Form 8938 and the FBAR covers those thresholds.

A UK pension does not need to move when you do, and moving it is rarely simple. Growth inside a qualifying scheme has treaty protection for a US citizen, which survives your departure.

Transfers abroad raise a separate set of charges and conditions.

So the default of leaving the pension where it is usually costs nothing and avoids a great deal.

Our article on UK pensions under US rules sets out the treatment.

Which side of 5 April you leave changes your British year. Which side of 31 December you arrive changes your American one.

A move in February and a move in May produce different filings from identical facts.

Where the date is genuinely flexible, model both. We have seen a fortnight's difference change a five-figure outcome.

Where it is not flexible, at least know which year each item falls into before you go.

Returning within a few years raises the temporary non-residence rules, which can pull gains realised while abroad back into UK charge. That matters most for anyone who sold assets after leaving.

So a two-year posting is a different planning problem from a permanent move.

Decide honestly which one you are doing, and if the answer is uncertain, plan for the shorter one. Reversing an optimistic assumption later is expensive.

Sometimes, because arriving somewhere creates a residence there. A move to New York or California starts a state filing obligation from the day you establish residence, with its own rules and its own year.

Those states look at ties rather than at passports. A property, a driving licence and a family home all count.

Plan the arrival state alongside the departure country. People spend months on the British side and overlook the state entirely.

In our practice the state return is the filing clients least expect in a repatriation year.

Considerably more people than HMRC. Your employer, your bank, your pension provider, the electoral roll and, if you let the property, a letting agent all need telling. Your GP and the local council matter too, and council tax on an empty property is a real cost rather than an administrative one.

Your GP and the local council matter for practical rather than tax reasons, though council tax on an empty property is a real cost.

Write the list before you go and work through it. Each of these becomes harder to correct once post is arriving at an address you no longer control.

Gather rather than file. You want your P45, your payslips for the year, your P60 from the previous year and a note of your departure date.

Add statements for every UK account as at the date you leave, and a valuation of anything you are keeping.

Those documents are easy to obtain while you are here and awkward afterwards.

In our practice, clients who left with a folder spent about a third of what those who left without one did.

Considerably quieter than the departure year, with one British filing and one American one. The British return covers any continuing UK source and nothing else, while your American return reports everything with credit for the UK tax paid on those sources.

Your American return then reports everything, with credit for the UK tax on those sources.

That pattern repeats annually until the UK source ends. It is much simpler than the year of the move, which is worth knowing while the move feels overwhelming.

HMRC repayments after departure are slow rather than difficult. Expect weeks at best and months where a return is involved.

Keep a UK account open to receive one, or be prepared to give HMRC overseas bank details.

Chase in writing with the reference from your P85 or return. Telephone queues from abroad are an expensive way to ask a simple question.

Work through this in the month before departure where you can.

Take an illustrative departure. An American leaves London in July after three years, having been on PAYE throughout, and keeps her flat and lets it out.

She files a P85 and receives a refund, because a full year of allowances sat against four months of salary. She then files a UK return each year for the rental income as a non-resident.

Her American return covers the whole calendar year, with the credit relieving the UK tax she actually paid. The figures are illustrative; the two-filing pattern is standard.

First, filing a P85 while also in Self Assessment, which confuses rather than helps. Second, assuming departure ends all UK filing.

Third, ignoring the split year rules and reporting too much or too little. Fourth, closing the UK bank account before the refund arrives.

Fifth, letting a post-departure bonus be taxed as though you never left. Sixth, leaving without the P45.

Seventh, treating leaving the UK as a single event. It is a year with two halves, and the filings follow the halves rather than the flight.

We map the departure year across both calendars first, because that determines every filing that follows. Then we handle the British final position and the American return together, so the same figures appear on both.

Our UK Self Assessment service covers the final return and any continuing obligations such as rental income.

Tell us your departure date and what you are keeping, and we will set out the filings in order.