The Cross-Border Tax Guide to Selling a UK Home
Cross-border tax on the sale of a UK home involves three separate layers that rarely get discussed together: UK Private Residence Relief, the US Section 121 exclusion, and a hidden currency gain under Section 988 that can survive even when both main reliefs apply in full. Missing any one layer can turn a tax-free sale into a five-figure US tax bill.
By the TaxYork Cross-Border Tax Team — reviewed by a US-UK dual-qualified adviser (CPA / Enrolled Agent).
Do I have to pay tax in both the UK and the US when I sell my house?
Potentially yes. Most dual filers selling a genuine main home end up paying little or nothing once UK and US reliefs are applied correctly. The UK taxes the sale under its Private Residence Relief rules, while the US applies the Section 121 home sale exclusion separately, and each country calculates the gain on its own terms. The complication is that a third, uncapped tax charge can arise on the mortgage itself, quite apart from the property gain.
Why do two tax systems look at the same sale differently?
HMRC calculates the gain in sterling from the original purchase price to the sale price under its own Capital Gains Tax rules. In contrast, the IRS calculates gain in US dollars using the exchange rate on each relevant date under Section 121 of the Internal Revenue Code. A property that shows a modest gain in pounds can show a very different figure once converted, particularly after years of currency movement between the US dollar and sterling. This mismatch is the root cause of most surprises in cross-border tax cases we see at TaxYork, especially when selling a UK home.
Is my main home exempt from capital gains tax in the UK?
Private Residence Relief gives a full UK Capital Gains Tax exemption on the sale of your only or main home, covering the entire period of ownership provided you lived there throughout, did not let out part of the property, and the grounds are under 5,000 square meters. The final nine months of ownership always count towards relief even if you had already moved out, which helps sellers who relocate before completion.
When Private Residence Relief does not cover the whole gain
Letting part of the property, running a business from a dedicated room, or owning grounds larger than 5,000 square meters can all restrict full relief. Sellers who lived abroad for extended periods while still owning UK property should check the qualifying periods carefully against HMRC's HS283 help sheet before assuming full relief applies automatically. Full guidance on the underlying rules also sits on the main gov.uk tax when you sell your home page.
Relief or rule
What it covers
What it does not cover
UK Private Residence Relief
UK Capital Gains Tax on the property, full ownership period plus final 9 months
Letting relief beyond the final 9 months; grounds over 5,000 sq m
US Section 121 exclusion
Up to $250,000 single / $500,000 MFJ of US property gain
Section 988 currency gain on a foreign-currency mortgage
Section 988
Nothing — it creates a separate, uncapped ordinary-income charge
Losses are generally non-deductible; gains are fully taxable
Do US citizens pay capital gains tax on selling a UK property?
US citizens and green card holders remain taxable on worldwide gains, so a UK home sale must be reported on the US return regardless of UK relief. Section 121 allows a US taxpayer to exclude up to $250,000 of gain if single, or $500,000 if married filing jointly, provided the home was owned and used as the main residence for at least 24 of the 60 months before sale. This exclusion applies to a foreign home exactly as it would to a US one, so long as the ownership and use tests set out in 26 U.S. Code Section 121 are met.
How the ownership and use tests work in practice
The 24 months do not need to be consecutive, which helps dual filers who split time between the UK and the US. A seller who lived in the property for 30 months over the past six years, then rented it out before selling, can usually still claim the full exclusion. However, the rental period may trigger separate depreciation recapture rules that a US preparer needs to check line by line. Getting this timeline right is often the deciding factor in cross-border tax planning when selling a UK home, since a few months either way can change the outcome entirely.
Do I pay tax on currency exchange gains when I sell foreign property?
Yes, and this is the layer most dual filers never see coming. Section 988 treats the repayment of a foreign-currency mortgage as a separate transaction from the sale of the home itself, so if the dollar has weakened against sterling since the mortgage was taken out, repaying that GBP loan can generate an ordinary-income gain that Section 121 does not shelter at all. The de minimis rule only exempts personal foreign-currency gains of $200 or less per transaction, which rarely covers a full UK mortgage payoff, a point the IRS discusses in its own international practice unit on foreign currency transactions.
Why is this gain taxable, but the equivalent loss is often not??
The IRS treats a Section 988 loss on a personal transaction as generally non-deductible, while a matching gain is fully taxable, an asymmetry practitioners sometimes call the tax whipsaw. A seller who took out a £400,000 mortgage when sterling was strong against the dollar, then repaid it years later after the pound weakened, can face real ordinary income purely from the currency movement, even if the property itself sold at a loss in dollar terms.
What is the 60-day rule for capital gains tax in the UK?
Non-UK residents disposing of UK residential property must file a UK Capital Gains Tax return and pay any tax due within 60 days of completion, regardless of whether a gain or loss arises. This deadline applies even where Private Residence Relief reduces the UK gain to nil, because the relief does not waive the filing obligation itself, and it is one of the most commonly missed steps when selling a UK home in a cross-border tax sale.
Rebasing for non-resident sellers
Non-residents disposing of UK residential property generally rebase the cost of the property to its market value as at 5 April 2015, so only the appreciation since that date is normally within the scope of UK Capital Gains Tax. Getting an April 2015 valuation from an RICS surveyor before filing is essential, since HMRC can query an unsupported figure and the 60-day clock does not pause for a valuation dispute.
Case study: a dual filer selling a London home after relocating to Texas
A husband and wife, both US citizens, bought a house in Richmond, London, in 2014 for £620,000 with a sterling mortgage, lived there as their only home until relocating to Houston in 2022, and sold it in 2026 for £980,000 after their tenant vacated. Private Residence Relief covered the UK gain in full because the final nine months of ownership counted automatically.
On the US return, the couple qualified for the full $500,000 Section 121 exclusion since they had owned and lived in the property for well over 24 of the previous 60 months at the point of sale. Their preparer still identified a $31,000 Section 988 ordinary-income gain on the mortgage payoff, caused entirely by dollar weakness against sterling since 2014, a liability that neither PRR nor Section 121 could touch. Handling cross-border tax in UK home scenarios like this one is precisely why the currency layer needs to be checked before the sale completes, not after.
How does the sale interact with FBAR, FEIE, and estate planning?
Sale proceeds sitting in a UK bank account will usually push balances over the FBAR reporting threshold. If the sterling mortgage was in a foreign currency, the exchange rate history matters for years afterward. If the sale proceeds sat in an unreported UK account, streamlined catch-up may apply. However, sellers with a genuinely reasonable explanation should also consider that if undisclosed foreign accounts surface during a home sale, the reasonable cause route can sometimes apply instead.
Large sale proceeds can also matter more than sellers expect, since large UK sale proceeds can affect worldwide estate exposure once the US estate tax rules for citizens are considered, a point explored in our guide to US estate tax on worldwide assets for dual filers. Sellers moving funds abroad afterward should also keep an eye on the UK Inheritance Tax rules if proceeds remain in a UK estate at death, since the wider financial picture around cross-border tax on the sale of a UK home rarely ends at completion.
Why the Foreign Earned Income Exclusion will not help here
Some sellers assume the Foreign Earned Income Exclusion, worth $132,900 for 2026 under Revenue Procedure 2025-32, might shelter part of the property gain. It will not, because the FEIE doesn't shelter capital gains, only earned income, as we set out in our guide to the Foreign Earned Income Exclusion for dual filers, and a home sale gain is investment income under US law, not wages or self-employment earnings.
What should I do before listing a UK property for sale?
Get a formal RICS valuation dated as close to 5 April 2015 as is practical if the property was owned before that date, since this figure anchors the non-resident CGT computation. Pull together the original mortgage documents showing the GBP amount borrowed and the exchange rate at drawdown, because this is the only way to quantify Section 988 exposure before completion rather than after the funds have already moved.
If the sale is timed around a move back to the US, selling before or after repatriating changes your residency-based reliefs, as we cover in the cross-border tax guide to returning to the US. Hence, the completion date deserves as much planning attention as the asking price.
Coordinating the UK and US filing deadlines
The 60-day NRCGT filing sits on a completely different clock from the annual US Form 1040 deadline, and missing the UK window creates penalties independent of anything owed to the IRS. Sellers who also hold sale proceeds destined for family members should note that gifting sale proceeds to UK family triggers Form 3520 reporting on the US side, a point we explain fully in the cross-border tax guide to gifting wealth to UK family, and a requirement confirmed on the IRS's own About Form 3520 page that is easy to overlook once the property itself has been dealt with. Filers with older undisclosed accounts unrelated to the sale itself may also want to review reasonable cause as an alternative to streamlined filing before the completion date locks in their reporting position.
Getting cross-border tax selling a UK home right before completion
Selling a UK home while filing US taxes is not a problem to solve after completion, because the 60-day NRCGT clock and the Section 988 currency calculation both need figures gathered in advance. TaxYork's dual-qualified advisers model the UK and US positions side by side, flag any currency gain on the mortgage before you commit to a completion date, and prepare both the NRCGT return and the US disclosures in parallel. Contact hello@taxyork.com or call 020 3488 8606 to arrange a pre-sale review, or visit taxyork.com to see how we support dual filers through the entire transaction.