The Complete 2026 US Expat Tax Guide for Americans Living in the UK

If you are an American living in the UK, your tax situation is more complex than most people realise and more manageable than most people fear. The United States taxes its citizens on worldwide income regardless of where they live, which means moving to London does not end your IRS obligations. But it does not mean you pay tax twice either. With the right approach, the right forms and the right specialist guidance, most Americans in the UK owe little or nothing to the IRS after their UK taxes are accounted for.

At Jaffe & Co, as trusted tax advisors London expats have relied on since 1981, we navigate this landscape daily for ourselves as US citizens and for our clients across London and worldwide. This is the guide we wish every newly arrived American had on their first day in the UK.

Your Core US Filing Obligation

Every US citizen and green card holder living in the UK must file a US Form 1040 annually reporting worldwide income to the IRS regardless of whether any US tax is ultimately owed. This obligation exists even if you pay full UK income tax through PAYE, have lived in the UK for decades, or hold no US bank accounts.

The filing deadline for Americans abroad is June 15, an automatic two-month extension beyond the standard April 15 domestic deadline, with a further extension to October 15 available on request. Tax owed, however, is still due by April 15, after which interest begins to accrue on any unpaid balance.

How to Avoid Paying Tax Twice

The most important concept for every American expat in the UK is the Foreign Tax Credit, and understanding it properly is the difference between an anxious filing experience and a straightforward one.

The FTC allows you to offset taxes already paid to HMRC against your US tax liability on the same income dollar for dollar. For most Americans in the UK, a high-tax jurisdiction, the FTC reduces or eliminates US income tax liability on employment income. The UK's income tax rates are generally higher than US rates, which means the credit typically covers the full US liability.

The alternative tool is the Foreign Earned Income Exclusion, which excludes up to $132,900 of foreign earned income from US taxation in 2026. For most Americans in the UK, the FTC is the stronger strategy, but the right choice depends on your specific income profile, and making the wrong decision costs you unnecessarily.

What You Must Report Beyond Your Tax Return

Filing Form 1040 is the beginning, not the end of US compliance for Americans in the UK.

FBAR (FinCEN Form 114): If the aggregate value of all your non-US financial accounts, including UK current accounts, savings, ISAs, pensions, and digital banking platforms, exceeded $10,000 at any point during the year, FBAR filing is required. Non-wilful violations carry penalties starting at $16,536 per account in 2026.

Form 8938 (FATCA): If your total foreign financial assets exceeded $200,000 at year-end as a single filer, Form 8938 is required alongside your tax return. This is entirely separate from FBAR filing; one does not satisfy the other.

Form 8833: If you are taking a treaty-based position on pension income or employer contributions, this disclosure must be filed with your 1040. Treaty benefits are never automatic; they must be actively claimed.

As specialist US tax preparation services providers, we include all of these in every client engagement as standard practice, not as optional additions.

ISAs and UK Pensions: The Two Biggest Surprises

ISAs: The UK's Individual Savings Account is tax-free under HMRC rules, but the IRS does not recognise this exemption. Every pound of interest, dividends, and capital gains inside your ISA must be reported on your US individual income tax return as ordinary taxable income. UK-domiciled funds inside a Stocks and Shares ISA may also qualify as Passive Foreign Investment Companies, triggering Form 8621 reporting and potentially punitive tax treatment.

UK Pensions: All UK pension income is taxable on your US return as ordinary income. The 25% tax-free lump sum that UK law allows is fully taxable in the US without careful advance planning. Employer pension contributions may be reportable as current-year income unless a treaty election is correctly made via Form 8833.

These two areas produce the most expensive and most avoidable mistakes and where specialist guidance makes the clearest financial difference.

The New FIG Regime: A 2026 Development

From April 2025, the UK introduced the Foreign Income and Gains regime, a four-year exemption from UK tax on foreign income for eligible new UK arrivals. For US citizens, opting in creates a significant complication: income exempt from UK tax cannot benefit from the Foreign Tax Credit on the US return, meaning the IRS may collect more, not less. Opting in also causes you to forfeit the UK Personal Allowance of £12,570. For most American expats, the FIG regime is not beneficial once both systems are modelled together.

Making Tax Digital: New From April 2026

Self-employed Americans and landlords in the UK earning above £50,000 annually must now comply with Making Tax Digital, maintaining digital records and submitting quarterly updates to HMRC. This creates a new compliance layer that must be carefully coordinated with US annual filing. A single adviser handling both UK and US obligations produces significantly better outcomes than two separate advisers working independently.

If You Have Missed Prior Years of Filing

The IRS Streamlined Foreign Offshore Procedure allows qualifying non-willful filers to come into full compliance by filing three years of returns and six years of FBARs, paying any tax owed plus interest. Most expats find they owe little or nothing after applying the Foreign Tax Credit to back returns. This procedure is only available before the IRS initiates contact; the right time to act is always now.

FAQs

Do I have to file a US tax return if I pay full UK income tax through PAYE? Yes, the US filing obligation is based on citizenship, not residency; PAYE does not satisfy the annual Form 1040 requirement.

Is the Foreign Tax Credit or FEIE better for Americans in the UK? For most Americans in the UK, the Foreign Tax Credit is the stronger strategy; UK tax rates are generally high enough to eliminate US liability when applied correctly.

Does my UK ISA need to be reported to the IRS? Yes, ISA income is fully taxable on your US return, and ISA accounts count toward FBAR reporting thresholds regardless of their UK tax-free status.

What is the penalty for missing an FBAR filing? Non-wilful FBAR violations carry penalties starting at $16,536 per account per year in 2026  even when no tax is owed and UK compliance is complete.

Can Jaffe & Co help if I have not filed US returns for several years? Yes, we guide clients through the IRS Streamlined Foreign Offshore Procedure to achieve full compliance with significantly reduced or eliminated penalties for qualifying situations.