US Citizens in the UK: IRS, FBAR & HMRC Reporting Guide

For a US citizen in the UK, reporting is the part of cross-border life that causes the most anxiety and the most avoidable trouble. The reassuring truth is that the two systems are built to work together: pay tax once, claim the credit, and you are generally not taxed twice. The risk is not double taxation; it is the web of information returns that sit on top of the tax, where honest people get caught out simply because nobody told them the forms existed.

This article is for US persons resident in the UK, and dual-filers generally, who want a clear map of what to report, to whom, and at what thresholds.

The basic principle: you file in both countries

The US taxes its citizens and green-card holders on worldwide income wherever they live; the UK taxes its residents. Soa US person in the UK files a UK Self Assessment return and a US federal return, each covering worldwide income. To stop the same income being taxed twice, foreign tax credits and the US-UK treaty allow tax paid in one country to offset tax owed in the other. In most cases this means paying broadly the higher of the two rates overall, not both in full.

The US information returns that bite on UK accounts

The FBAR (FinCEN Form 114)

If your foreign financial accounts together reach $10,000 at any point in the year, you must file an FBAR reporting them. This is a single, fixed threshold with no adjustment for filing status or living abroad, and it captures UK current accounts, savings, ISAs, investment accounts, and pensions. It is filed separately from your tax return.

Form 8938 (FATCA)

Once your specified foreign financial assets exceed the FATCA thresholds, you also file Form 8938 with your US return. The thresholds are higher for those living abroad - broadly $200,000 at year-end or $300,000 at any time for single filers (and $400,000 / $600,000 for married filing jointly) - compared with much lower thresholds for US residents. Form 8938 overlaps with, but does not replace, the FBAR; many people file both.

Form 8621 (PFICs)

Each PFIC you hold - most non-US funds qualify - generally needs its own annual Form 8621. This is where holding UK funds turns into a recurring reporting burden, and another reason US persons often hold individual shares or US-domiciled funds instead.

Foreign-trust forms

Some arrangements, including certain self-directed pensions such as SIPPs, can raise foreign-trust reporting on Forms 3520 and 3520-A. A relief procedure removes those forms for some tax-favoured foreign retirement arrangements, but it may not extend to participant-directed schemes like SIPPs, so whether it applies depends on the structure and should be confirmed.

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The UK side

On the UK side, a US person who is UK-resident is generally taxed on the arising basis - worldwide income and gains as they arise - and reports through Self Assessment. New arrivals may instead use the four-year Foreign Income and Gains regime that replaced the non-domicile remittance basis from 6 April 2025, sheltering foreign income and gains during the initial period. UK tax actually paid then feeds the foreign tax credit calculation on the US side, which is why the two returns must be prepared with an eye on each other rather than in isolation.

How to check your dual-reporting requirements

A simple framework helps. First, list every account and asset, UK and US, with its highest balance in the year. Second, test the US information thresholds: anything pushing foreign accounts over$10,000 means an FBAR; foreign assets over the FATCA thresholds mean Form 8938;any non-US fund means Form 8621; certain trusts mean the 3520 series. Third, map the income: every source belongs on both returns, with credits aligned. Fourth, confirm the UK basis: arising, or FIG for a recent arrival. Working through those four steps each year keeps the picture honest and surfaces problems before a deadline does.

An illustrative example

Consider a hypothetical US citizen, age 45,two years into life in London, who diligently files her US return reporting her salary but has never filed an FBAR — unaware that her UK current account, savings, and a small ISA together passed $10,000 long ago, and that the ISA's funds are PFICs needing Form 8621. Nothing about her situation is aggressive; she simply did not know the information returns existed. A structured review brings her filings current and prevents the problem compounding. This example is hypothetical and for illustration only.