US–UK Year-End Tax Planning 2026: The Deadlines and Numbers That Matter Before 31 December

Cross-border filers get two year ends, ten weeks apart. Decisions that look identical — realising a gain, making a gift, topping up a pension — can land in different tax years in each country depending on which side of 31 December or 5 April they fall. This guide collects the dates and the 2026 figures we have verified against primary sources, so you can see what is actually worth doing before each deadline.

Short answer

Before 31 December 2026 (US tax year end): review realised gains and losses, use the $19,000 annual gift exclusion (or $194,000 to a non-citizen spouse), and check any new UK fund purchases for PFIC exposure. Before 31 January 2027: file your UK Self Assessment for 2025/26 and pay what is due. Before 5 April 2027 (UK tax year end): use UK allowances — and, if you are a former remittance-basis user, note that 2026-27 is the final year of the Temporary Repatriation Facility's 12% rate. And on 28 October 2026 the UK Budget may change the UK side of this list — we will update this guide after the speech.

The 2026 US numbers, from the IRS

These figures come from Revenue Procedure 2025-32 and apply to US tax year 2026 — the return you will file in early 2027:

Two of these reward action before 31 December. The annual gift exclusion does not carry over: a $19,000 gift made on 31 December and another on 1 January moves $38,000 without touching your lifetime exclusion, while waiting until January halves what this year lets you do. The same logic applies to the $194,000 non-citizen-spouse exclusion — relevant to many of our clients whose husband or wife is British, because unlimited marital transfers only apply when the recipient spouse is a US citizen.

Deadlines between now and April

• 28 October 2026 — the UK Budget. The date was confirmed by the Chancellor in July. Treat pre-Budget speculation as exactly that; decisions worth accelerating purely on rumour are rare.
• 31 December 2026 — last day of the US tax year. Capital gains and losses, gifts, and charitable deductions for 2026 all settle on this date.
• 15 January 2027 — final 2026 quarterly estimated payment for US filers who pay as they go.
• 31 January 2027 — UK Self Assessment online filing and payment deadline for the 2025/26 year, including the first payment on account for 2026/27.
• 5 April 2027 — UK tax year end: ISA allowance, CGT annual exempt amount, pension annual allowance, and the TRF's 12% rate (below) all reset or expire.
• 15 April 2027 — 2026 US returns and FBARs due; expats get an automatic filing extension to 15 June and FBARs extend automatically to 15 October.

Before 31 December: the US side

Gains and losses. US capital-loss harvesting only works against the US year end — and for UK residents the same disposal also lands in the UK's 2026/27 year, usually at different rates with a different allowance (£3,000 annual exempt amount in 2025/26). Model both sides before selling; the saving in one country can be smaller than the cost in the other, and the US wash-sale rule and the UK's 30-day share-matching rule disagree about buying back.

Charitable giving. Donations to US charities are generally not deductible for UK tax, and Gift Aid donations to UK charities are generally not deductible on the US return — timing a gift for 31 December only helps if the charity's status matches the return you are claiming it on. Dual-qualified charities exist for exactly this problem.

PFIC check before you buy. If year-end bonuses are heading into investments, remember that most UK funds, index trackers and ETFs — including everything inside a Stocks & Shares ISA — are PFICs to the IRS. Checking before purchase costs nothing; unwinding after costs Form 8621 work at best.

Before 5 April: the UK side

The TRF's last 12% year. Former remittance-basis users can designate pre-April 2025 foreign income and gains under the Temporary Repatriation Facility at a flat 12% — but only until 5 April 2027. The final year, 2027-28, charges 15%, and then the facility closes. If you have legacy offshore funds you ever intend to bring to the UK, this is the planning window with an actual price on it.

FIG regime arrivers. New UK arrivers within their first four years of residence can receive foreign income and gains free of UK tax under the FIG regime — but the clock runs on tax years of residence, not on use. If 2026/27 is year two, nothing extends the window.

Allowances that reset. The £20,000 ISA subscription limit (US filers: see the PFIC point above before using it for funds), the £3,000 CGT annual exempt amount, and unused pension annual allowance from 2023/24 (which drops out of the three-year carry-forward after 5 April 2027) all work on a use-it-or-lose-it basis.

What about the Budget?

We do not plan around leaks. The Budget lands on 28 October 2026; if it changes anything material to US–UK filers — rates, allowances, the FIG or TRF rules — the change will have a commencement date, and that date is what planning hangs on. We will update this guide once the documents are published.

Sources

• IRS Rev. Proc. 2025-32 — 2026 inflation adjustments (FEIE, gift exclusions, estate exclusion, standard deduction)
• GOV.UK — Chancellor's letter confirming the Budget date of 28 October 2026
• GOV.UK — Self Assessment deadlines
• IRS — Report of Foreign Bank and Financial Accounts (FBAR)

US figures: tax year 2026. UK figures: tax year 2025/26 unless stated; the 28 October 2026 Budget may change 2026/27 onwards. This is general information, not advice on your facts.