What Nobody Tells You About US Tax Living in the UK

You’ve landed your dream life in Britain — a flat in a leafy postcode, a job you love, weekends in the Cotswolds. The last thing on your mind is the IRS. But if you hold a US passport or green card, the taxman in Washington may still have a claim on your income, no matter how long you’ve been paying HMRC.

In reality, US expat taxes in the UK can involve both systems. The UK may tax you because you live or work there, while the United States may still require you to file because you are a US citizen or green card holder. For a deeper breakdown of double taxation, FBAR, FATCA, ISAs, pensions, and UK tax residency rules, Flamingo Compliance has a practical guide to US expat taxes in the UK.

Do expats pay taxes after moving to the UK?

The simple answer to “do expats pay taxes?” is: often, yes — but the more important question is where, on what income, and what reporting is required.

For Americans living in Britain, there are usually two separate questions:

First, are you taxable in the UK? This depends on your UK income, your residence position, and HMRC rules.

Second, do you still need to file with the IRS? For many US citizens and green card holders abroad, the answer is still yes if they meet the filing threshold. The United States generally taxes citizens and resident aliens on worldwide income, even when they live abroad.

That does not automatically mean you will pay twice on the same income. Relief mechanisms such as the Foreign Tax Credit, the Foreign Earned Income Exclusion, the US-UK tax treaty, and the Totalization Agreement can reduce or prevent double taxation in many cases. But filing and reporting obligations can still apply even when the final US tax bill is low or zero.

The PAYE trap: “I already pay UK tax, so I’m done”

One of the most common mistakes around taxes for US expats in the UK is assuming that PAYE solves everything.

Imagine a US citizen working in London for a UK employer. Their salary is taxed through PAYE. From a UK perspective, this may cover much of their income tax position. But from a US perspective, they may still need to file a US tax return, report their UK salary, and claim Foreign Tax Credits for tax paid to HMRC.

This is where US citizens working in UK taxes become more complicated than expected. The issue is not always whether more tax is due. Often, the issue is whether the right forms are filed, the right income is reported, and the right relief is claimed.

For many Americans, the surprise is psychological. They are not trying to avoid tax. They simply assume that one developed tax system must somehow “talk to” the other. It usually does not work that neatly.

UK tax residency still matters

Even though the US taxes citizens differently from most countries, UK tax residency is still a major part of the picture.

HMRC uses the Statutory Residence Test to decide whether someone is a UK tax resident. Spending 183 days or more in the UK during a UK tax year usually makes someone a UK tax resident, but people can also become resident with fewer days if they have enough UK ties, such as a home, family, or work.

This is where US tax living in the UK becomes more than a filing question. Your number of UK days can affect whether HMRC taxes you as a UK resident, whether certain UK regimes apply, and how your UK tax position interacts with your US filing.

For people who travel frequently between the UK, US, Europe, and other countries, day-counting can become surprisingly fragile. A few extra trips, a delayed return, or a longer-than-planned stay can change the picture.

That is why tools like Flamingo Compliance exist. The app is designed for internationally mobile people who need to track tax residency, visa limits, and physical presence across countries, with reports they can share with advisors. Flamingo positions itself as a compliance tracking app, not a tax advisor — useful when the practical problem is evidence, dates, and records rather than interpretation alone.

The accounts that catch Americans off guard

Another reason US expat taxes UK searches are so common is that normal UK financial products can look very different from the IRS perspective.

An ISA is a classic example. In the UK, an Individual Savings Account can be tax-efficient. But for US tax purposes, it may not receive the same treatment. Income, gains, or underlying investments may still need to be reported.

UK pensions can also be complex. Workplace pensions and SIPPs may involve treaty considerations, and the treatment can depend on the pension type, contributions, growth, and withdrawals. Even the UK’s 25% tax-free lump sum can raise US questions.

Then there are PFIC rules. Many ordinary non-US funds, ETFs, and investment trusts can create extra US reporting and potentially unfavorable tax treatment. What feels like a normal UK investment choice may create an unexpected US tax admin burden.

FBAR and FATCA: reporting even when no tax is due

For many Americans abroad, the tax bill is not the only issue. Account reporting can matter just as much.

If the total value of foreign financial accounts exceeds $10,000 at any point during the year, an American may need to file an FBAR. This is an aggregate threshold, not a per-account threshold. A current account, savings account, and investment account can together trigger reporting even if no single account looks especially large.

FATCA reporting may also apply through Form 8938 if foreign financial assets exceed certain thresholds. Again, the issue is not necessarily that extra tax is owed. The issue is that the IRS may still expect disclosure.

This is why US taxes for expats in the UK are often less about one dramatic tax bill and more about staying organised across two systems.

What usually goes wrong

Most mistakes happen because people rely on memory, assumptions, or old advice.

They assume UK tax replaces US filing. They forget FBAR because each account is below $10,000. They treat ISAs as tax-free everywhere. They choose the Foreign Earned Income Exclusion without comparing it to the Foreign Tax Credit. They ignore former US state tax residency. Or they assume the US-UK treaty removes the need to file a return.

The pattern is familiar: nothing feels urgent in year one. Then, after a few years abroad, someone speaks to an advisor, applies for a mortgage, sells an investment, changes visa status, or starts catching up on filings — and suddenly the missing records matter.

The practical takeaway

The best way to think about US tax for expats in the UK is not “Will I be taxed twice?” but “What do I need to file, report, prove, and track?”

Living in Britain does not automatically end US tax filing obligations. Paying HMRC does not automatically close the IRS side. And being under one country’s tax system does not mean the other country disappears.

For Americans in the UK, the safest habit is to keep clean records early: income, accounts, investments, travel days, and residency position. Tax advisors can interpret the rules, but they still need accurate information to work with.

That is where tools like Flamingo Compliance can be useful. The tax residency and visa tracking app helps internationally mobile people monitor travel days, residency thresholds, visa limits, and physical presence across countries, so they have clearer records to share with advisors when questions come up.