The first thing to be clear about is that moving abroad does not end your US filing obligation. Citizens and Green Card holders report worldwide income every year, wherever they are living. What changes is not whether you file but how the numbers get there.
This piece walks through the four things that genuinely change when you file from the UK: the reliefs available, the disclosure forms that appear, the deadlines, and the order the two countries' returns need to be prepared in.
Two reliefs do most of the work
The Foreign Earned Income Exclusion takes a slice of employment income out of the US calculation entirely — $130,000 for the 2025 tax year and $132,900 for 2026, indexed annually. Foreign tax credits instead give you dollar-for-dollar credit for tax already paid to HMRC, across every income type, with excess credits carrying forward for 10 years.
They are not interchangeable, and the choice compounds. Because UK tax rates usually exceed US ones, credits alone often wipe the US bill while building a carryforward buffer — and they keep IRA contributions and refundable child tax credits available, which the exclusion can cost you. Revoking the exclusion later locks you out of it for five years, so the first year's choice deserves modelling, not a software default.
The forms with no UK equivalent
You also pick up filing obligations that simply do not exist in the UK system. FBAR reporting is triggered by the combined high balance of your non-US accounts crossing $10,000 at any point in the year — an aggregate test, measured at each account's annual peak, that an ordinary London salary crosses without noticing. It carries no tax, only a disclosure duty and meaningful penalties for missing it.
Form 8938 stacks a second, higher-threshold disclosure on top for larger asset totals, and holding UK funds — including inside an ISA — can add PFIC reporting on Form 8621. None of these forms changes the tax you owe; all of them change the risk of getting the paperwork wrong.
Deadlines shift, and order matters
Living abroad gives you an automatic filing extension to 15 June, with a further extension to 15 October on request — though payment is still due 15 April, and interest runs from that date on anything unpaid. The FBAR nominally shares the April date but auto-extends to October.
The extra room is genuinely useful, because a US return prepared before the UK position is settled often has to be revisited. The UK tax year ends 5 April and Self Assessment figures firm up over the summer; preparing the two returns together, in the right order, is what makes the credits land cleanly instead of approximately.