Most Americans who buy a home in Britain take out a sterling mortgage. It feels like the most ordinary loan in the world. You borrow pounds, you repay pounds, and the bank never mentions dollars.
The IRS does mention dollars. It measures what you borrowed and what you repaid in its own currency. When the exchange rate moves in between, a foreign currency mortgage can produce a taxable gain. No cash profit sits behind it. This guide explains how that happens and what you can plan.
What is a foreign currency mortgage?
It is a home loan in a currency other than the one your tax return uses. For a US citizen or green card holder, that currency is the dollar. So a sterling mortgage on a London home is a foreign currency mortgage, however local it feels.
Nothing about the loan itself is unusual. The interest rate, the term and the repayments work exactly as they would for a British borrower.
The difference is purely in how the American return measures it. Every pound borrowed and every pound repaid has a dollar value on the day it moves.
How does a gain appear when you repay?
It appears when the pound buys fewer dollars at repayment than it bought when you borrowed. You received a certain number of dollars in value at the start. You then hand back fewer dollars in value to clear the same pounds.
The IRS can treat that shortfall as a gain to you. It is real in dollar terms, even though your pound balance simply went from the loan amount to zero.
The reverse is also possible. If the pound strengthens, clearing the loan costs you more dollars than you received. That is a loss, and the next section explains why it does not help.
| Step | In pounds | In dollars |
|---|---|---|
| Borrow at $1.30 per pound | £300,000 | $390,000 |
| Repay at $1.20 per pound | £300,000 | $360,000 |
| Result | Nothing gained or lost | $30,000 gain |
| Repay at $1.40 per pound instead | £300,000 | $420,000 |
| Result | Nothing gained or lost | $30,000 loss, not deductible |
Why is the loss not deductible?
Because the loan financed a personal home rather than a business or an investment. Losses on personal transactions are generally not deductible for individuals. So the tax rules give you the gain when the pound falls and nothing when it rises.
People often call this a one-way street, and the description is fair. You carry the currency risk in both directions, but the tax system only counts one of them.
That asymmetry is the main reason the issue deserves attention. On average, it tilts against the borrower over a long mortgage.
Can you net the loan against the house?
No. In Revenue Ruling 90-79, the IRS treated a foreign currency mortgage and the home it financed as two separate transactions. A loss on one cannot reduce a gain on the other.
So a home that falls in value does not shelter a currency gain on the loan. Equally, a currency loss on the loan does not reduce a taxable gain on the house.
This catches people who assume the two belong together because they were bought together. The purchase and the borrowing belong together commercially, but not for this purpose.
Where does Section 988 fit in?
Section 988 is the part of the tax code that deals with foreign currency transactions. However, it expressly carves out personal transactions entered into by individuals. A loan on your own home is a personal transaction.
That means the special Section 988 rules do not govern your home loan. The gain still exists under the general rules, and the loss is still personal.
The character of the resulting gain is a technical question, and the answer turns on the facts. We would not rely on a general article for it, and neither should you.
When does a repayment actually happen?
Every repayment of principal is, in principle, a repayment for this purpose. In practice, the regular monthly amounts are small. The events that usually matter are the sale of the home, a refinance and a large overpayment.
A refinance with a new lender clears the old loan in full. That can realize the whole currency movement since you first borrowed, even though you still own the house.
A product switch with the same lender is less clear. Whether it counts turns on whether the lender actually discharges the original loan. So check the paperwork before assuming either way.
Does Britain tax the same movement?
Generally not for a sterling borrower living in Britain, and that surprises many people who expect the two systems to agree. Sterling is the British system's own currency. So borrowing and repaying pounds produces no currency result there.
That has a knock-on effect. Where Britain charges no tax on the gain, there is no British tax to credit against the American charge.
Our guide to avoiding double taxation explains how credits normally work. Here they simply have nothing to work with.
Does the currency gain affect your mortgage interest?
No, the two are separate items on the return. The currency result comes from repaying principal. Interest is a cost of borrowing, and it only matters on your return if you itemize deductions.
Where you do itemize, you convert the interest paid each year into dollars. Most Americans in Britain take the standard deduction instead, so the interest rarely changes the answer.
Keep the annual lender statement anyway. It shows interest and principal separately, which is exactly the split this calculation needs.
Which exchange rates do you use?
Use the rate on the day the money moved, both at drawdown and at repayment. A foreign currency mortgage gain depends on two specific dates, so a yearly average rate is the wrong tool here.
The IRS does not publish an official daily rate of its own. Its page on foreign currency and exchange rates says to use a consistently applied rate. It also lists its yearly average rates, which suit regular income better.
The Treasury also publishes reporting rates of exchange each quarter. Whatever source you choose, record it next to the figures and use it consistently.
How does this interact with selling the home?
A sale usually brings both calculations into the same year. You work out the gain on the house in dollars and apply any exclusion you qualify for. Then you work out the mortgage result separately.
The home sale exclusion applies to the house, not to the loan. So even a fully sheltered sale can leave a taxable currency gain on the mortgage.
The IRS guide to selling your home covers the exclusion itself. Our guide to selling a UK home as a US person covers both sides of a British sale.
What happens if you move back to the United States?
Moving does not end the exposure while the loan stays open. A foreign currency mortgage keeps its dollar measurement wherever you live. So the eventual sale or refinance can still produce a gain after you leave Britain.
Letting the home after a move changes the picture again. The loan may then finance a rental property rather than a personal home, and the rules for investment property differ.
That shift deserves advice at the time you start letting. Our guide to UK rental income on a US return covers the reporting that follows.
What can you actually plan?
You cannot control the exchange rate, and nobody should try to trade around it for tax reasons. What remains within your control is smaller, but it is real, and it is mostly about when you act. Timing is the lever.
A refinance or a large overpayment is usually a choice. Knowing roughly where the pound stands against your borrowing rate lets you see the tax effect before you commit.
In our practice we see this most often with refinancing. People refinance for a better rate and discover a currency gain the following spring. A short calculation beforehand would have shown it.
What records make this easy later?
Four documents do almost all the work. Keep the mortgage offer, the completion statement, the annual lender statements and any redemption statement. Together they show every date and amount you will need.
Add the exchange rate beside each key date as you go. Our exchange rate lookup helps with the yearly figures you use elsewhere on the return.
Store all of it with your property file. The same records support the calculation on the house when you eventually sell it.
Handling a foreign currency mortgage, step by step
This list takes an hour to set up and saves a great deal of reconstruction later.
Keep the results with your other property records, since the same documents support the eventual sale.
- Find the drawdown date and amount on the original mortgage offer or completion statement.
- Record the exchange rate for that date, and note the source.
- Log each large overpayment, refinance or redemption with its date and amount.
- Record the exchange rate on each of those dates, using the same source.
- Work out the dollar difference for each repayment event.
- Check any joint mortgage, since only your share belongs on your return.
- Model a refinance or sale before you commit to it.
An illustrative example
Take an illustrative example: an American engineer in Leeds borrows pounds to buy a house. At the time, the pound is strong against the dollar. Several years later, the pound has weakened.
She refinances with a different lender to get a lower rate. The new lender clears the old loan in full. In dollar terms, she repays noticeably less than she borrowed, which produces a gain on her return for that year.
She still owns the house, and she has received no cash. Her British colleague with an identical mortgage has nothing to report, because sterling is his own currency.
Common mistakes with a sterling mortgage
The first is assuming nothing happens until you sell the house. A refinance can realize the full currency movement years earlier.
The second is trying to offset a currency loss. On a personal home loan, that loss is not deductible and cannot be set against the house.
The third is losing the drawdown records. Without the original date and amount, the calculation turns into guesswork a decade later.
How US UK Tax Hub helps
We calculate currency results on mortgages through our US federal returns service, alongside the property sale where there is one. Where a refinance is coming, we can model it first.
If you have a sterling mortgage and a decision ahead, send us the loan details. We will set out the position at a fixed fee agreed first. This article is general information, not personal tax advice; take advice on your own facts from a qualified adviser.