Property Across the Atlantic: Buying, Letting and Selling in Two Tax Systems

One asset, two complete rulebooks

Own property in one country while taxable in the other and every event in the property's life — purchase, letting, refinance, sale — is measured twice, under rules that agree on almost nothing but the address. The US computes everything in dollars, the UK in sterling; the US taxes calendar years, the UK April years; and each applies its own reliefs to its own version of the numbers. Credits reconcile the totals eventually, but only if both computations are done properly and the timing mismatch is managed.

Letting: two different profit figures

The recurring shock for landlords is that the two returns rarely show the same profit:

• Depreciation. The US requires residential buildings to be depreciated in computing rental profit, and claws the benefit back on sale. The UK does not depreciate residential property at all.
• Mortgage interest. The UK restricts relief for residential landlords to a basic-rate credit; the US generally deducts rental interest in full.
• Expenses and losses follow different rules on each side, and losses trapped in one system cannot offset the other's profit.

So a UK letting can show a HMRC loss and an IRS profit in the same year — with real tax due to one country and nothing to credit from the other. Non-resident owners add their own layer: the UK's Non-resident Landlord scheme for UK property, and US withholding rules for foreign owners of US rentals.

Currency: the tax on exchange rates

Two currency effects surprise almost everyone:

On sale, the US computes gain in dollars: sale proceeds at completion-date rates against cost at purchase-date rates. A London flat that went nowhere in sterling can show a six-figure dollar gain — or the reverse — purely from exchange-rate movement across a long ownership.

On the mortgage, US rules can treat repaying or refinancing a sterling debt as generating a taxable foreign currency gain if the dollar cost of discharging the debt fell while it was outstanding. The UK does not recognise the event, so the US tax stands alone, uncreditable — one of the genuine double-tax pockets in the US–UK system. The asymmetry stings: equivalent currency losses on a personal mortgage are generally not deductible.

Neither effect appears on any UK document. They exist only in the dollar ledger a US filer must keep from the day of purchase.

Selling: the 60-day clock and the annual one

The UK now expects CGT on UK residential property to be reported and paid within 60 days of completion where tax is due — a separate online return, well inside the Self Assessment cycle, and applying to non-resident sellers too. The US taxes the same sale through the ordinary annual return for the calendar year of sale. Sequencing matters for credits: which country's tax is paid first, and in which of each other's years it lands, determines how smoothly relief flows.

The main-residence mismatch

Both countries relieve gains on your own home; they do not relieve the same amount. UK private residence relief can eliminate the entire gain on a property occupied as your main residence throughout, with absences handled by formula. The US home sale exclusion is a capped dollar amount per taxpayer (an inflation-unindexed cap — see the IRS figures), with the excess taxable. A long-held family home can therefore be entirely tax-free to HMRC and still produce a substantial US bill — driven by house-price growth and currency movement together — with no UK tax available to credit against it. For US citizens in the UK selling the family home, this single mismatch is often the largest tax event of their expat years, and the one most worth modelling before exchange of contracts.

Before you transact

Property decisions worth pricing in both systems before committing: whose name goes on title (spouses may be taxed very differently, especially with a non-US spouse), whether to repay or refinance a sterling mortgage in a favourable rate window, when to sell relative to a move, and how depreciation claimed today reshapes the eventual sale. Every one of these is cheap to decide early and expensive to discover late — usually on a completion statement that can no longer be amended.