US Person Selling UK Property: Capital Gains in Both Countries

US person selling UK property: an introduction

A US person selling UK property reports the sale to two tax authorities that measure the gain in different ways. The UK works in pounds and often exempts a main home completely. The United States works in dollars and caps its exemption. Therefore, a sale that is tax free in Britain can still produce a US bill.

This article explains how each country taxes a US person selling UK property, why the two figures differ and where sellers get caught. Furthermore, it covers the deadlines and the records to keep. Our full guide to US-UK double taxation and the treaty sets out the wider rules on gains and credits.

Why a US person selling UK property faces two tax systems

The United States taxes its citizens and green card holders on worldwide income and gains, wherever they live. Britain taxes its residents on the same basis. Consequently, an American living in London falls into both nets at once. The treaty does not remove either charge on property. Instead, the foreign tax credit prevents the same gain being taxed twice in full.

The two calculations at a glance

The UK computes the gain as sale price less cost, both in pounds. The US converts the purchase price into dollars at the rate on the purchase date. It then converts the sale price at the rate on the sale date. As a result, a move in the exchange rate becomes part of the US gain. In our experience, this single difference causes most of the surprises.

How does the UK tax the sale?

The UK charges capital gains tax on the sterling gain, unless private residence relief covers it. For a main home, that relief usually removes the whole gain. For a rental flat or a second home, tax is normally due.

Private residence relief on a main home

Private residence relief exempts the gain on a property that has been your only or main home throughout your ownership. The relief has no upper limit. Furthermore, the final nine months of ownership always qualify, even if you have moved out. HMRC explains the conditions in its guidance on tax when you sell your home.

However, periods when the home was let can fall outside the relief. Letting relief is now narrow. Specifically, it applies only where you let part of the home while living there yourself, as HMRC's rules on letting out part of your home set out.

Rates on rental and second properties

Where relief does not apply, the UK taxes the gain at 18% within the basic rate band and 24% above it. HMRC publishes the figures on its page for Capital Gains Tax rates. Additionally, each person has an annual exempt amount, shown under Capital Gains Tax allowances. That amount is £3,000 for the 2026-27 tax year.

The 60-day UK return

If UK tax is due on a residential property, you must report the sale and pay within 60 days of completion. You do this through HMRC's service to report and pay Capital Gains Tax on UK property. No return is needed from a UK resident when relief covers the whole gain. Importantly, the 60-day payment also helps on the US side, as explained below.

How does the US tax the same sale?

The United States taxes the dollar gain at 0%, 15% or 20% when you have owned the property for more than a year. For a main home, an exclusion removes the first $250,000 of gain, or $500,000 on a joint return. Anything above that is taxable.

The section 121 exclusion

The exclusion is in section 121 of the Internal Revenue Code. You qualify if you owned the home and lived in it as your main home for two of the five years before the sale. The IRS explains the tests in Publication 523 and in Topic 701 on the sale of your home.

Notably, the amounts are fixed in the statute and do not rise with inflation. London prices have risen a great deal. Consequently, long-term owners often exceed the limit. Moreover, the $500,000 figure needs a joint return. Where your spouse is not American and does not file, only your share of the gain is counted, against a $250,000 exclusion.

The gain is measured in dollars

The US gain uses the exchange rate on each date. The IRS publishes yearly average exchange rates, although a sale needs the rate for the actual day. Therefore, a US person selling UK property can show a larger or smaller gain in dollars than in pounds. If the pound has weakened since you bought, the dollar gain shrinks. If it has strengthened, the dollar gain grows.

The Net Investment Income Tax

Higher earners can owe a further 3.8% on the taxable part of the gain. The IRS describes this on its page for the Net Investment Income Tax. Whether foreign tax credits can offset it is disputed, so we treat it as a real cost when we run the numbers.

Rental and second properties

A US person selling UK property that was never their home gets no exclusion at all. The whole dollar gain is taxable. Furthermore, the US expects depreciation to be deducted from rental income each year, whether or not you claimed it. That depreciation reduces your cost. Consequently, it increases the gain on sale, and that part is taxed at up to 25%. Therefore, the US figure for a rental flat is rarely the simple difference between two prices.

What is the mortgage currency trap?

The mortgage currency trap is a taxable US gain that arises when you repay a sterling mortgage with pounds that cost fewer dollars than the pounds you borrowed. It is separate from the gain on the property. Furthermore, it has no UK equivalent, so no UK tax exists to credit against it.

Why repaying a sterling mortgage can be taxable

The IRS treats the loan as its own transaction. You borrowed a dollar amount and repaid a different dollar amount. Therefore, any saving is a currency gain. The underlying rules on foreign currency are in section 988 of the Internal Revenue Code. In contrast, a loss on the mortgage, when the pound has risen, is personal and not deductible. Practitioners disagree on whether the gain is ordinary income or capital gain.

An illustrative example

Consider a typical case. Emma is a single US citizen who bought a London flat for £500,000 when the pound stood at $1.60. Her dollar cost was $800,000. She borrowed £400,000, which was $640,000 at that rate. Years later, she sells for £900,000 at $1.30, which is $1,170,000.

The UK gain of £400,000 is fully covered by private residence relief, so the UK tax is nil. However, the US gain is $370,000. After the $250,000 exclusion, $120,000 is taxable, and at 15% that is $18,000. In addition, repaying the mortgage costs only $520,000. The $120,000 difference is a separate currency gain. Hence, a sale that Britain treats as exempt produces two US charges.

How do you avoid paying tax twice?

You avoid double tax by claiming a foreign tax credit in the United States for the UK tax paid on the same gain. The credit is claimed on Form 1116. Because UK rates on property are now usually higher than US rates, the credit often covers the whole US charge.

The foreign tax credit on Form 1116

The IRS explains the credit on its foreign tax credit page and on its page for Form 1116. Take a rental flat as an example. Suppose the UK gain is £120,000 and the UK tax is about £28,000. The US gain on the same sale is $75,000, taxed at 15%, or $11,250. The UK tax, converted into dollars, exceeds that figure. Therefore, the credit removes the US tax and leaves a surplus to carry forward.

However, the credit cannot help where the UK charged nothing. That is why a US person selling UK property that was their main home can still owe US tax. Additionally, the mortgage currency gain has no UK tax to match it.

A home owned jointly with a British spouse

Many Americans in Britain own their home with a spouse who is not a US person. In that case, the US usually counts only the American half of the gain. However, only one $250,000 exclusion is then available. Electing to file jointly doubles the exclusion, but it brings your spouse's worldwide income into the US net. Hence, a US person selling UK property with a British spouse should compare both routes before the sale.

Timing the UK payment

The two countries use different tax years. The US taxes the gain in the calendar year of sale. Meanwhile, the UK tax year runs to 5 April. Paying the UK tax within 60 days usually places it in the same US year as the sale. Otherwise, the credit can arrive a year too late to match the gain. Consequently, you should decide the payment plan before completion, not when the US return is due.

What records and deadlines matter?

Keep the purchase and sale completion statements, the exchange rate on each date and evidence of every improvement. Without them, the dollar calculation cannot be done properly. Moreover, good records often reduce the US gain.

Records to keep

Improvement costs increase your cost for both countries. A new kitchen, an extension or a loft conversion all count. For the US, each cost is converted at the rate on the date you paid it. Therefore, keep the invoices with their dates. Similarly, keep every mortgage statement, because each capital repayment and each remortgage can produce its own currency calculation.

Deadlines on both sides

Any UK tax on a residential sale is due within 60 days of completion. The US return for the year of sale is due on 15 April, with an automatic extension to 15 June for Americans abroad. A further extension to 15 October is available on request. In practice, a US person selling UK property should tell their preparer before exchange of contracts, so both computations are ready.

If you have already sold without reporting

Some sellers assume that a tax-free UK sale needs no US reporting. That is a common and honest mistake. However, the sale still belongs on the US return for that year. If earlier returns are missing or wrong, a formal catch-up route is the safe fix. Our guide to IRS Streamlined Filing explains how it works. Importantly, acting before the IRS makes contact keeps the penalty-free route open.

How US UK Tax Experts can help

We prepare both computations from the same file. First, we work out the UK gain and any relief. Next, we rebuild the dollar cost from your completion statement and improvement records. We then calculate the mortgage position and the credit. In addition, we file the 60-day UK return where one is due and report the sale on both annual returns.

Our property and capital gains service covers sales of homes and rental property. Furthermore, we prepare US and UK tax returns together, so the credit claimed in one country matches the tax paid in the other.

Conclusion

In summary, a US person selling UK property needs two calculations, one in pounds and one in dollars. UK relief can exempt a main home in full, while the US exclusion stops at $250,000 or $500,000. The exchange rate and the mortgage can each add to the US figure. However, where UK tax is due, the foreign tax credit usually covers the US charge.

Therefore, gather your records early and model both sides before you accept an offer. Ultimately, the cost of the sale depends less on the price than on the preparation.

Contact us

Are you a US person selling UK property this year, or have you sold one without reporting it to the IRS? Email us at hello@usuktaxexperts.com. Alternatively, send a short description of your situation through our contact page. We reply within one working day with the filings that apply and the dates that matter.