U.S. taxes in the UK: what 🇺🇸 Americans in London actually need to know

UK tax overview for 🇺🇸 Americans — why the Foreign Tax Credit dominates

The United Kingdom is one of the world's most popular destinations for American expatriates — approximately 325,000 U.S. citizens live there, concentrated in London's finance, technology, media, and professional services sectors. The UK operates a progressive income tax system with rates starting at 20% (the basic rate), rising to 40% (higher rate) on income above £50,270, and reaching 45% (additional rate) on income above £125,140. On top of income tax, employees pay National Insurance contributions — currently 8% on earnings between £12,570 and £50,270 per year, and 2% on earnings above that upper limit.

For U.S. citizens, this tax burden is significant — but it is also the key to their U.S. tax strategy. The United States taxes its citizens on worldwide income regardless of residence, but it also provides the Foreign Tax Credit (FTC) as a mechanism to avoid double taxation. When you pay UK income tax on the same income that the U.S. would also tax, you can claim a credit for the UK taxes paid against your U.S. tax liability on that income.

In most cases, the UK's tax burden — particularly for higher earners in London — exceeds the equivalent U.S. tax that would be owed on the same income. A basic-rate UK taxpayer paying 20% plus 8% National Insurance is already at 28% effective rate, which often exceeds the comparable U.S. marginal rate on that income after standard deductions and the U.S. progressive bracket structure. For higher earners, the gap is even larger. This is why the FTC — not the Foreign Earned Income Exclusion — is the standard planning tool for 🇺🇸 Americans in the UK.

The UK tax year runs from April 6 to April 5 — not the calendar year. This mismatch with the U.S. January-through-December tax year creates complexity when claiming the FTC, because you are crediting taxes paid in a UK tax year that spans two U.S. tax years. The IRS allows you to use UK taxes paid in a UK tax year as FTC in the U.S. tax year in which the UK taxes accrue (i.e., the year the income was earned), which is generally the most favorable approach. Your tax advisor should document this election clearly on your return.

The ISA trap — the biggest mistake 🇺🇸 Americans in the UK make

Even if the IRS does not treat your ISA as a foreign trust, the income and gains inside the ISA are still taxable by the United States on an annual basis. Any dividends earned within a stocks and shares ISA must be reported as dividend income on your U.S. return. Any capital gains realized within the ISA on the sale of shares are U.S.-taxable capital gains — not sheltered the way they would be under UK rules.

The practical guidance for 🇺🇸 Americans in the UK is stark:

• Do not open an ISA without first consulting a tax advisor who specializes in U.S. expatriate taxation and is familiar with the foreign trust treatment question.
• If you already have an ISA — particularly a stocks and shares ISA — you need to assess whether Form 3520/3520-A filings are required for past years and whether you should continue contributing.
• Cash ISAs are lower-risk from a foreign trust perspective (the cash account structure is less likely to be characterized as a trust), but interest earned is still U.S. taxable income and must be reported.
• Lifetime ISAs (LISAs) and Innovative Finance ISAs have additional complications and should be approached with extreme caution.

The IRS has been somewhat inconsistent in how aggressively it pursues the foreign trust characterization of ISAs specifically, and there is genuine uncertainty in the tax law on this point. Some practitioners argue that a simple cash ISA does not meet the trust definition. However, the risk is real enough that the standard advice among U.S. expat tax specialists is to avoid ISAs entirely, and to address any existing ISAs with professional help.

US-UK tax treaty — key provisions and tie-breaker rules

The Convention Between the Government of the United States of America and the Government of the United Kingdom of Great Britain and Northern Ireland for the Avoidance of Double Taxation and the Prevention of Fiscal Evasion with Respect to Taxes on Income and on Capital Gains — known simply as the US-UK tax treaty — is one of the most comprehensive bilateral tax agreements the United States has signed. It was originally enacted in 1975 and most recently updated with a protocol in 2001, with additional technical corrections since.

Residency and tie-breaker rules

For tax purposes, both the U.S. and the UK may consider you a resident — the U.S. because you are a citizen, and the UK based on your physical presence and domicile. The treaty's tie-breaker rules (Article 4) determine which country has primary taxing rights when both claim you as a resident. The tie-breaker test looks at:

1. Where you have a permanent home available to you
2. Where your center of vital interests is (personal and economic relations)
3. Where you have your habitual abode
4. Nationality

For most 🇺🇸 Americans living and working in the UK, the UK will be the treaty-resident country, which means the UK has primary taxing rights over your employment income and most other income. The U.S. retains residual taxing rights as the citizenship country, and the FTC mechanism prevents double taxation.

Dividend and interest withholding

The treaty reduces withholding tax rates on cross-border dividends and interest. U.S.-source dividends paid to UK residents face a reduced withholding rate of 15% (or 5% for substantial holdings of 10% or more). UK-source dividends paid to U.S. residents are generally not subject to UK withholding tax. Interest paid between the two countries is generally exempt from source-country withholding under the treaty.

Capital gains

Article 13 of the treaty addresses capital gains. Real property gains are taxable in the country where the property is located. Other capital gains are generally taxable only in the country of residence — which for 🇺🇸 Americans living in the UK means the UK has primary taxing rights. The U.S. still taxes the gain as the citizenship country, but the FTC prevents double taxation.

Saving clause

The treaty contains a "saving clause" (Article 1) which provides that the U.S. retains the right to tax its citizens as if the treaty had not entered into force. This means that most treaty benefits designed to reduce taxation are not available to reduce U.S. citizens' U.S. tax obligations — they are primarily designed to prevent double taxation rather than eliminate U.S. tax entirely.

UK pension contributions — treaty treatment

UK workplace pensions — including auto-enrollment pension schemes, defined benefit schemes, and SIPP (Self-Invested Personal Pension) contributions — are the subject of significant US-UK treaty protections that many 🇺🇸 Americans in the UK are unaware of.

Under Article 18 of the US-UK treaty, contributions made by a U.S. citizen working in the UK to a UK employer pension plan that is recognized under UK tax law are deductible in calculating U.S. taxable income, subject to certain conditions and limitations. In practical terms, this means:

• Employer contributions to a qualifying UK pension on your behalf are generally not currently taxable as compensation in the U.S.
• Employee contributions to a qualifying UK employer scheme may be deductible for U.S. purposes, analogous to 401(k) pre-tax contributions.
• Pension income in retirement from a UK pension scheme is generally taxable in the country of residence at the time of receipt under the treaty — if you are living in the U.S. when you retire and draw a UK pension, it will be taxable in the U.S.

The treaty pension protections require that you make an election on your U.S. tax return to apply Article 18. This election must be made on a timely filed return (including extensions) and applies to the specific pension arrangements identified. Working with a CPA who understands this election is important — failing to make the election on time can be costly to correct.

FTC vs FEIE in the UK — why FTC wins for almost everyone

🇺🇸 Americans abroad have two primary mechanisms to avoid double taxation on foreign-earned income: the Foreign Earned Income Exclusion (FEIE, Form 2555) and the Foreign Tax Credit (FTC, Form 1116). In the UAE or Qatar — zero-tax jurisdictions — FEIE is the right tool because there are no foreign taxes to credit. In the UK, the analysis is fundamentally different.

Why FTC is almost always better in the UK

The UK's income tax rates are high enough that, for most income levels and filing situations, the UK taxes paid on earned income will exceed the U.S. tax that would be owed on the same income. When UK taxes exceed U.S. taxes on a dollar-for-dollar basis, the FTC eliminates your U.S. liability entirely. There is no remaining U.S. tax to pay.

FEIE, by contrast, has a hard exclusion cap — $130,000 for 2025 (adjusted for inflation). If you earn £150,000 as a London banker, FEIE cannot exclude the full amount. More importantly, even if your income were below the FEIE limit, using FEIE in the UK means you are giving up the ability to use FTC on that excluded income in future years — and if you ever want to switch back from FEIE to FTC, you need IRS permission (Form 2555 revocation) and cannot switch back to FEIE for 5 years.

When FEIE might still make sense in the UK

FEIE may occasionally be preferable for 🇺🇸 Americans in the UK in very specific situations:

• Low earners who are below the UK personal allowance (£12,570) and therefore paying minimal UK tax — the FTC would be small, and FEIE may be more efficient
• 🇺🇸 Americans in their first year in the UK who arrived mid-year and have mixed U.S. and UK income for the year
• Self-employed individuals with complex income sourcing questions

In all other cases — which means virtually all salaried American employees in the UK — the Foreign Tax Credit is the correct and superior strategy.

National Insurance and the US-UK totalization agreement

National Insurance (NI) is the UK's social security contribution system. Employees pay Class 1 NI contributions on their earnings. The current rates are 8% on earnings between £12,570 and £50,270 per year, and 2% on earnings above £50,270. Employers additionally pay 13.8% employer NI on earnings above the secondary threshold.

For U.S. citizens, the question arises: do I owe both UK National Insurance and U.S. Social Security and Medicare taxes on the same wages? Without a totalization agreement, the answer would potentially be yes — creating a crushing double social security burden. Fortunately, the United States and the United Kingdom have a totalization agreement (officially the Agreement on Social Security Between the United States and the United Kingdom).

How the US-UK totalization agreement works

The totalization agreement determines which country's social security system you pay into, based on your employment situation:

• UK local hires: If you work in the UK as a local employee (regardless of citizenship), you pay UK National Insurance and are exempt from U.S. Social Security and Medicare taxes on those wages. Your UK NI contributions count toward UK State Pension eligibility.
• Seconded U.S. employees: If your U.S. employer sends you to work in the UK on a temporary assignment (generally up to 5 years), you may continue paying U.S. Social Security and Medicare taxes and be exempt from UK National Insurance. This requires a Certificate of Coverage from the Social Security Administration.
• Self-employed: Self-employed 🇺🇸 Americans in the UK pay UK NI contributions (Class 2 and Class 4) and are generally exempt from U.S. self-employment tax (which covers Social Security and Medicare) on the same earnings.

UK National Insurance contributions do not generate a U.S. Foreign Tax Credit — they are social security levies, not income taxes. However, they do reduce your UK taxable income indirectly in some scenarios, and they count toward your eligibility for the UK State Pension, which has its own U.S. tax reporting implications when received in retirement.

FBAR for UK accounts — Barclays, HSBC, NatWest, and more

Any U.S. person whose combined foreign financial account balances exceed $10,000 at any point during the calendar year must file an FBAR (FinCEN Form 114) by April 15 (with an automatic extension to October 15). For 🇺🇸 Americans living and working in the UK, this threshold is almost universally exceeded — a monthly salary deposited to a UK current account will typically cross $10,000 within weeks.

UK accounts commonly requiring FBAR reporting include:

• Current (checking) accounts — Barclays, HSBC, NatWest, Lloyds, Santander UK, Halifax, and any other UK high street or online bank
• Savings accounts — all UK savings accounts, including those offered by building societies such as Nationwide, Yorkshire Building Society, and Coventry Building Society
• ISA accounts — cash ISAs and stocks and shares ISAs are foreign financial accounts and must be reported on the FBAR if the combined threshold is exceeded, regardless of any UK tax-free status
• UK investment and brokerage accounts — accounts held with Hargreaves Lansdown, Interactive Investor, AJ Bell, Vanguard UK, or any other UK investment platform
• UK Premium Bonds — National Savings and Investments (NS&I) Premium Bonds are reportable if balances exceed the threshold
• UK pension accounts — the FBAR treatment of UK pension accounts is unsettled; some practitioners report them, others do not. The safer approach is to report them and let the IRS determine they do not qualify rather than fail to report and face penalties.
• UK employer share plan accounts — accounts holding shares acquired through UK tax-advantaged share schemes (SIP, SAYE, EMI) may be reportable

The FBAR is filed electronically via the BSA E-Filing System at bsaefiling.fincen.treas.gov. It is not filed with your tax return. The deadline is April 15 with an automatic (no-action-needed) extension to October 15. Penalties for willful non-filing are severe — up to the greater of $100,000 or 50% of account balances per violation per year. Non-willful penalties are up to $10,000 per violation, and the Supreme Court's 2023 decision in Bittner v. United States held that non-willful penalties are assessed per-form rather than per-account, limiting non-willful exposure somewhat.

RSUs, bonuses, and equity compensation in London finance and tech

London is home to a large population of American finance and technology professionals who receive significant equity compensation — Restricted Stock Units (RSUs), stock options, and performance shares — in addition to cash salaries and bonuses. The UK and U.S. tax treatment of these instruments overlaps but differs in important ways.

Restricted Stock Units (RSUs)

When RSUs vest, the shares are considered employment income in both the UK and the U.S. In the UK, HMRC taxes the fair market value of shares at vesting through PAYE — your employer is required to withhold income tax and National Insurance on the value of shares at vest. In the U.S., the same event is also compensation income taxable as wages.

The good news: because both countries tax the same event — vesting — the UK tax paid at vest is generally eligible for the U.S. Foreign Tax Credit against the corresponding U.S. tax. Most 🇺🇸 Americans in the UK with RSUs will find that the FTC fully offsets their U.S. tax liability on RSU income, because the UK effective rate on higher-band income (40-45% plus NI) typically exceeds the U.S. rate on the same income.

After vesting, if you hold the shares and they subsequently appreciate before sale, the post-vest appreciation is a capital gain. The UK taxes this gain with the capital gains annual exemption and CGT rates (18% or 24%). The U.S. taxes it as a long-term capital gain if held for more than a year (0%, 15%, or 20% depending on income) or short-term if held for a year or less. The FTC treatment on post-vest capital gains depends on whether you are still in the UK at the time of sale — if so, UK CGT paid will be available as FTC against U.S. capital gains tax.

Stock options — NQSO vs ISO

Non-Qualified Stock Options (NQSOs) are taxed at exercise in both countries — the spread between exercise price and market value is compensation income. UK HMRC taxes through PAYE; IRS taxes as wages. The same FTC logic applies.

Incentive Stock Options (ISOs) have more complex treatment. The ISO spread at exercise is not regular income but is an Alternative Minimum Tax preference item for U.S. purposes. UK law does not recognize the ISO preferential treatment — HMRC taxes the exercise spread as employment income. This mismatch can create situations where UK tax is paid but no corresponding U.S. regular income tax is owed at exercise, meaning the FTC may not be fully usable in the exercise year.

Bonuses and deferred compensation

Cash bonuses are straightforward earned income in both countries. The year in which the bonus is taxable may differ — the UK generally taxes bonuses in the year paid or received, while the U.S. rules for deferred compensation (Section 409A) apply to arrangements where payment is deferred. For most standard annual bonuses paid within 2.5 months of year-end, the timing is the same in both countries.

UK tax-advantaged share schemes

UK employers frequently offer share schemes that are tax-advantaged under UK law: Share Incentive Plans (SIPs), Save As You Earn (SAYE/Sharesave), and Enterprise Management Incentives (EMIs). These schemes provide significant UK tax benefits — reduced or zero NI on exercise, beneficial CGT treatment on disposal. However, U.S. tax law does not recognize these UK-specific advantages. 🇺🇸 Americans participating in these schemes generally owe U.S. tax on the same events that the UK scheme structure tries to minimize, creating potential for suboptimal outcomes. Review participation carefully before enrolling.

Non-dom status — historical context after April 2025 abolition

For decades, one of the UK's most distinctive tax features was the concept of "non-domicile" (non-dom) status. Under the old rules, individuals who were UK resident but not UK domiciled could elect the remittance basis of taxation — meaning they only paid UK tax on overseas income and gains that they actually brought into (remitted to) the UK. Overseas income left offshore was not subject to UK tax. This made the UK remarkably attractive for wealthy international residents, including 🇺🇸 Americans.

This regime largely ended on April 6, 2025. The UK government abolished the remittance basis for new arrivals and significantly curtailed it for existing claimants. As of the 2025-26 UK tax year, the UK has moved to a residence-based tax system. Individuals who have not been UK resident in any of the 10 prior tax years enjoy a 4-year "foreign income and gains" (FIG) exemption in their early years of UK residence — but this is a much more limited relief than the old non-dom regime.

Historically, the non-dom regime created planning complexity for 🇺🇸 Americans specifically, because the U.S. taxes worldwide income regardless of domicile. An American claiming the remittance basis in the UK was potentially paying UK tax only on remitted income while owing U.S. tax on all worldwide income — meaning the FTC generated only from remitted income was available to offset U.S. tax. The abolition of the remittance basis simplifies this in some ways: UK and U.S. taxable income are now more closely aligned, making FTC calculations more straightforward for most 🇺🇸 Americans.

Practical filing steps and UK-specific forms

1. Determine your primary strategy: FTC vs FEIE. For most UK-based 🇺🇸 Americans, this will be FTC. Confirm this with a CPA who can model both options against your actual income profile before committing.
2. Gather UK income documentation. Collect your P60 (end-of-year tax summary from employer), P11D (benefits in kind), and payslips for the UK tax year. If your UK employer uses the standard PAYE system, your P60 is the closest equivalent to a U.S. W-2. Note: the P60 covers April 6 to April 5, not the U.S. calendar year — conversion will be needed.
3. Complete Form 1116 (FTC). Categorize your foreign taxes paid into the correct income baskets — general limitation (for wages and active business income) and passive (for dividends, interest). The basket segregation matters for the FTC calculation.
4. Address the UK tax year mismatch. Decide whether to use the accrual method (credit UK taxes accrued in the U.S. year the income was earned) or the paid method (credit UK taxes actually paid in the U.S. year). Document your election clearly on the return.
5. File the FBAR by April 15 (automatic extension to October 15) at bsaefiling.fincen.treas.gov. Report all UK bank accounts, savings accounts, ISA accounts, and investment accounts if your combined balances exceeded $10,000 at any point during the year.
6. Consider Form 8938 (FATCA) if your total foreign assets exceed the higher thresholds applicable to 🇺🇸 Americans living abroad.
7. Apply the pension treaty election if you are contributing to or receiving employer contributions in a qualifying UK pension. This election must be made on a timely filed return — do not miss it.
8. Address ISA reporting. If you hold an ISA, assess with a specialist whether Form 3520/3520-A filings are required for any past or current years.
9. File Form 1040 by June 15 (the automatic two-month extension for 🇺🇸 Americans abroad). Extend to October 15 with Form 4868 if more time is needed. A further extension to December 15 is available by written request for overseas filers.
10. Submit a UK Self Assessment return if HMRC requires it. Most employees taxed fully through PAYE do not need to file, but those with investment income, self-employment income, rental income, or complex situations typically do.