US Tax Deadlines for Expats: What Wealthy US-UK Clients Should Know The US tax deadlines expats must meet do not stop at 15 April. Living in the UK automatically grants an extension to 15 June. However, interest still runs from April, FBAR and foreign-trust forms follow their own calendar, and everything sits awkwardly against the […]
The US tax deadlines expats must meet do not stop at 15 April. Living in the UK automatically grants an extension to 15 June. However, interest still runs from April, FBAR and foreign-trust forms follow their own calendar, and everything sits awkwardly against the UK’s 6 April tax year. Missing one date can cost far more than the tax itself.
By the Jungle Tax Cross-Border Tax Team — reviewed by a US-UK dual-qualified adviser (CPA / Enrolled Agent).
Your Form 1040 is technically due 15 April 2026 for the 2025 tax year, but as a US citizen or green card holder resident abroad on that date, you receive an automatic two-month extension to 15 June 2026. You do not file anything to claim it — being outside the United States and Puerto Rico is enough. The catch is that this extension covers filing only, not payment: interest on any balance owed accrues from 15 April regardless of when you actually file.
For wealthy clients with investment income, rental portfolios or business profits, that distinction matters. The US tax deadlines expats rely on are really two separate clocks — one for lodging the paperwork and one for settling the bill — and the Internal Revenue Service treats them very differently. The IRS guidance for citizens and resident aliens abroad sets this out in full.
The practical upshot is that a high earner who waits for the automatic June extension without paying anything in April is already accruing interest from the first day of the extension, resulting in a six-figure liability that quietly adds up over the weeks leading up to filing. Where a balance is likely, we advise clients to make a good-faith payment by 15 April — even an estimate — so the interest clock is stopped on the bulk of the bill while the detailed return is finalized. It is a small discipline that routinely saves clients more than our fee would cost.
If June is not enough, filing Form 4868 extends your filing deadline to 15 October 2026. Abroad filers who want the full extension should submit it by 15 June rather than 15 April. Beyond that, a discretionary extension to 15 December is available on written request to the IRS, though it is granted sparingly and is not a right. None of these extensions moves the payment date — a point we labor with every client, because it is where avoidable interest quietly builds.
Wealthy clients often assume that because they are always due a refund, extensions are irrelevant to them. That assumption is dangerous. Foreign tax credits and the foreign earned income exclusion are claimed on a filed return; until the return is lodged, the IRS has no record of the reliefs that wipe out your liability. A late or unfiled return can therefore convert a nil-tax position into an assessed balance with penalties attached. Our US tax return service is built around filing early enough to leave room for the UK figures you need.
Below is the deadline calendar we give to US-UK clients. Diarising these US tax deadlines, which expats commonly overlook, is the single cheapest piece of tax planning available.
|
Obligation |
Standard date |
Extended date
|
|---|---|---|
|
Form 3520-A (calendar-year foreign trust) |
15 March 2026 |
15 September 2026 (Form 7004) |
|
Form 1040 filing |
15 April 2026 |
15 June (auto, abroad), then 15 October (Form 4868) |
|
Balance of tax due (interest runs) |
15 April 2026 |
No extension available |
|
Q1 estimated tax |
15 April 2026 |
— |
|
FBAR (FinCEN Form 114) |
15 April 2026 |
15 October 2026 (automatic) |
|
Q2 estimated tax |
15 June 2026 |
— |
|
Q3 estimated tax |
15 September 2026 |
— |
|
Discretionary extension |
— |
15 December 2026 (on request) |
|
Q4 estimated tax |
15 January 2027 |
— |
Quarterly estimated payments fall on 15 April, 15 June and 15 September 2026, with the final installment on 15 January 2027. Clients with dividend, interest, or self-employment income that is not subject to withholding usually need to pay these to avoid an underpayment penalty. The IRS estimated tax pages confirm the schedule.
The trap for US-UK clients is that the estimated tax rules make little allowance for the UK tax you are simultaneously paying to HMRC. Your foreign tax credit is settled when the return is filed, but the IRS expects payments across the year on income that the UK may tax months later. Building a safe-harbor payment plan — usually pegged to the prior year’s liability — avoids penalties. At the same time, your final credit position is calculated, and it is one of the US tax deadlines that expats most often trip over. This is a routine part of our cross-border tax planning for clients with substantial unwithheld income.
Yes. The FBAR — FinCEN Form 114 — is due 15 April 2026, with an automatic extension to 15 October 2026 that requires no application. If your combined non-US accounts exceeded USD 10,000 at any point in 2025, you must file. Wealthy UK-resident clients almost always cross that threshold once current accounts, ISAs, pensions, and joint holdings are added together.
The FBAR is filed separately from your tax return, through FinCEN rather than the IRS, and penalties for non-wilful failure are severe. The IRS FBAR overview explains who must report, and the actual filing is made on the FinCEN BSA E-Filing system. Do not assume your accountant has filed it simply because your 1040 is done — the two are different lodgements on different systems.
Form 8938 under FATCA reports specified foreign financial assets and is filed with your 1040, so it follows the same extended deadlines. It overlaps with, but does not replace, the FBAR — many clients must file both. The reporting thresholds are higher for those living abroad, but wealthy portfolios easily meet them.
The distinction matters because the two forms count different things and answer to different authorities. The FBAR captures accounts you control; Form 8938 captures assets you own, including certain foreign shares, interests in non-US funds, and some pension rights. A client can breach one threshold and not the other, or both. Reviewing the whole balance sheet once a year, ahead of the season, is the only reliable way to know which forms apply. Our US expat tax team runs that review as standard before any return is prepared.
Foreign trusts pull your calendar forward. For a calendar-year trust, Form 3520-A is due 15 March 2026 — a full month before the main season begins — with an extension to 15 September available via Form 7004. Form 3520, reporting your transactions with foreign trusts and certain large foreign gifts, is generally due with your 1040 and follows those extensions.
Many UK families hold structures that meet the US definition of a foreign trust without realizing it, including certain pension arrangements and family investment vehicles. The IRS guidance on Form 3520-A, its Form 3520 instructions, and the broader foreign trust reporting requirements set out the details. Penalties here start at USD 10,000 and climb, so the March date deserves a place at the very top of your diary.
The reason foreign trusts are so unforgiving is that the penalty is not tied to tax owed — it is tied to the value in the structure and the failure to report, even where no US tax is due at all. A dormant family trust generating modest income can still expose its US owner to a five-figure penalty for a missed information return. Where a client discovers historic non-compliance, the IRS’s delinquent international information return procedures and reasonable-cause statements offer a route back. Still, they work best before the IRS makes contact. Early, deliberate diarising of the 15 March date is far cheaper than any remediation.
The two systems run on different years, and that mismatch is where cross-border planning earns its keep. The US taxes the calendar year to 31 December; the UK taxes the year from 6 April to 5 April. UK Self Assessment returns are due by 31 October (paper) or 31 January online — so a UK online return covering 2025-26 is due 31 January 2027, per GOV.UK.
The consequence is a timing problem for foreign tax credits. UK tax paid in one period must be matched against US income in a different period, and getting the ordering wrong can strand a credit or trigger double taxation. Sequencing the two filings — often lodging the US return first, or deliberately extending it to capture finalized UK figures — is a core part of how we manage the US tax deadlines that expats juggle alongside HMRC. State filing deadlines add a further layer for anyone who has not cleanly severed US state residency.
In practice, the client who extends their US return to October is not being disorganized — they are often being strategic. Waiting until the UK Self Assessment position for the overlapping year is settled means the foreign tax credit can be claimed on final, not estimated, figures. That removes the need to amend later and reduces the risk of an IRS query. The judgment call is whether the interest cost of a later payment outweighs the certainty gained, and it is one we make with each client individually rather than by rule of thumb. For those unwinding US state ties, our US tax specialists also check whether a state return is still required.
An anonymized client — a London-based media executive with US citizenship, UK dividends and a family trust — came to us having filed her 1040 on time but missed the 15 March Form 3520-A deadline two years running. She had also assumed her accountant’s return covered her FBAR. The two returns had been prepared by different advisers who never spoke, so nobody owned the full picture.
We regularised the trust filings under the appropriate delinquent-return procedure, aligned her US and UK returns so her UK tax credited correctly against US income rather than being partly lost to a timing mismatch, and moved her onto a single diarised timetable covering every date in the calendar above. The exposure we headed off ran to five figures in penalties alone, before counting the double taxation the credit realignment recovered. The lesson she takes from it is simple: with cross-border affairs, one adviser must hold the whole timetable, not half of it.
If you hold assets and obligations on both sides of the Atlantic, a single missed date can undo a year of careful planning. Our cross-border team maps every deadline to your situation and files on time. Email hello@jungletax.co.uk, call 0333 880 7974, or visit jungletax.co.uk.
Yes. US citizens and green card holders resident abroad on 15 April receive an automatic two-month extension to 15 June to file Form 1040. No form is required, but interest on tax owed continues to accrue from 15 April.
The FBAR (FinCEN Form 114) is due 15 April 2026, with an automatic extension to 15 October 2026. It applies if your non-US financial accounts together exceeded USD 10,000 at any time in 2025.
Yes. Filing Form 4868 extends your filing deadline to 15 October 2026. Expats seeking the full extension should file it by 15 June. The extension covers filing only, never payment.
For a calendar-year foreign trust, Form 3520-A is due 15 March 2026, with an extension to 15 September available by filing Form 7004 using the trust’s EIN before the March deadline.
No. Every US filing extension leaves the payment date on 15 April. Interest, and potentially penalties, accrue on any unpaid balance from that date regardless of when you file.
