Most people treat the exchange rate as background noise, a number that affects what their money buys overseas but not what they owe the IRS. US tax law disagrees. IRC §988 makes currency movement a taxable event in its own right, separate from whatever deal produced it. Where this ambushes ordinary taxpayers is not a trading account, it is the day they pay off a foreign mortgage: a US person who borrowed abroad can owe ordinary income tax on a "gain" never received in cash, on a house that may have lost value.
What Does IRC Section 988 Actually Tax?
IRC §988 taxes the change in exchange rates between the date a transaction is booked and the date it is paid, and treats that change as a separate item of ordinary income or loss. Section 988(a)(1)(A) provides that foreign currency gain or loss on a §988 transaction is computed separately and treated as ordinary. Section 988(b) defines it as the amount attributable to exchange rate changes between the booking date and the payment date.
Two consequences follow. Character is fixed: holding a currency position for fifteen years does not convert the result into capital gain. The only escape is the §988(a)(1)(B) election for forward contracts, futures contracts, and options, which must be made and the transaction identified on the day the position is opened, and which is unavailable for a debt instrument. And the currency result is bifurcated from the economics underneath it, measured independently and often not allowed to offset them.
Which Transactions Count as Section 988 Transactions?
Section 988(c)(1)(B) lists the triggering transactions, and the list is broader than most taxpayers expect because it reaches ordinary borrowing and ordinary accruals, not just currency speculation.
Section 988 Transactions Under §988(c)(1)(B)
Statute- Acquiring a debt instrument, or becoming the obligor under one, denominated in or determined by reference to a nonfunctional currency (§988(c)(1)(B)(i)). Holding a foreign bond or lending abroad puts you on one side. The sleeper is the other side: a foreign currency loan, including a home mortgage, is a §988 transaction on the day you sign.
- Accruing any item of expense, gross income, or receipts payable or receivable later in a nonfunctional currency. Invoicing a foreign client in their currency creates exposure between invoice and payment.
- Entering into or acquiring a forward contract, futures contract, option, or similar instrument denominated in a nonfunctional currency.
The obligor half of that first item turns a household financing decision into a tax position. A US person who funds a home abroad with a local currency mortgage has, in the eyes of the Code, taken a short position in that currency. Nobody experiences it that way. The law measures it that way anyway.
Why Does Paying Off a Foreign Mortgage Create a Taxable Gain?
Because you borrowed a fixed number of foreign currency units and repay that same fixed number, but the dollar value of those units moved in between. Reg. §1.988-2(b)(6) sets the obligor's computation: translate the principal at the spot rate on the date you became the obligor, then subtract the principal translated at the spot rate on the date payment is made or the obligation is transferred or extinguished. A positive result is exchange gain, because you discharged a liability worth more dollars using currency worth fewer.
The illustrations at Reg. §1.988-2(b)(9) work the mechanic through. Example 6 runs it in the loss direction: an individual borrows £10,000 when the pound is worth $1.50 and repays when it has risen to $1.70, realizing an exchange loss because it now takes more dollars to retire the same debt. Reverse the rate movement and the sign reverses with it. When the dollar strengthens against the loan currency, the same formula produces gain.
Two details make this worse.
Refinancing usually counts. The trigger is payment, transfer, or extinguishment of the obligation, including a deemed disposition under §1001 from a material change in the instrument's terms. Refinancing with a new lender extinguishes the old loan outright, and a same-lender refinancing generally clears the §1.1001-3 significant modification threshold, so the currency position closes even though no money leaves the household. Selling the property and retiring the mortgage from the proceeds does the same.
There is no offset from the property side. The dollar strengthening that creates your mortgage gain is often the same movement that cut the dollar value of the house, and those do not net. Rev. Rul. 90-79 holds that the borrowing and repayment of the mortgage is a separate transaction from the purchase and sale of the residence. The First Circuit affirmed in Quijano v. United States, 93 F.3d 26 (1st Cir. 1996), rejecting a couple's attempt to offset a roughly $100,000 currency loss on a pound sterling mortgage against the gain on the UK home it financed, and refusing to treat the mortgage as an integrated hedge under §988(d). Symmetry is not available: the gain is reportable, the personal loss is not deductible under IRC §165(c).
A Worked Example: What Does the Gain Actually Look Like?
Foreign Mortgage Payoff, Worked
ExampleA US citizen buys an apartment in the eurozone, rents it out, and borrows €500,000 when the spot rate is €1 = $1.40. Years later she sells and retires the full €500,000 of principal, when the spot rate is €1 = $1.10.
- Principal at the borrowing date rate: €500,000 x $1.40 = $700,000
- Principal at the payment date rate: €500,000 x $1.10 = $550,000
- Reg. §1.988-2(b)(6) result (rental property): $700,000 minus $550,000 = $150,000 exchange gain. Had the apartment been her personal residence, §988 would not apply at all under §988(e)(1), but Rev. Rul. 90-79 measures the same two dates and produces the same $150,000 taxable gain.
That $150,000 is ordinary income under §988(a)(1)(A), and she never received it in dollars. The loan and the property are separate transactions, so the currency result stands on its own. Had this been her personal residence instead, §988 would not apply, the gain would still be taxable under Rev. Rul. 90-79, and any currency loss would be nondeductible under §165(c).
Real loans amortize, which makes the arithmetic longer but not different. Each principal payment is measured against the spot rate on the date you became the obligor, so a borrower paying down a foreign mortgage has been closing slices of a currency position all along. Reconstructing that history from years of foreign statements is the part that reliably needs a professional, and it is standard cross-border tax work rather than something a general preparer will surface on their own. One more moving part: the foreign currency you actually hand over is itself property. If you acquire the currency ahead of the payoff and it moves before you pay, you have a second, separate item under Reg. §1.988-2(a)(2) on disposing of that currency, which can add to or offset the principal result. Funding the payoff from same-day sale proceeds generally leaves it at zero.
Does the $200 De Minimis Rule Save You?
No, and this is the most common misunderstanding in this area. IRC §988(e)(2) excludes gain only where an individual disposes of nonfunctional currency in a personal transaction, and only to the extent the gain does not exceed $200. Retiring a mortgage is not a disposition of currency. Disposition of nonfunctional currency is its own trigger under §988(c)(1)(C), while a mortgage sits under §988(c)(1)(B)(i) as an obligation you took on, and its payoff is the closing of that separate position, so the exclusion never reaches it.
Three further limits are routinely overstated.
What §988(e) Does and Does Not Do
Caution- It is gain-only. §988(e)(2) suppresses gain and creates no deduction. Personal currency losses are separately shut off: §988(e)(1) turns off §988 treatment for personal transactions, and IRC §165(c) denies any deduction for losses not incurred in a trade or business or a transaction entered into for profit.
- It is per transaction, not annual. The $200 is a cliff, not a bracket. Once the gain on a transaction exceeds $200, the exclusion does not apply to that transaction at all.
- It only covers currency. Buying euros to fund your payoff and then spending them can be a currency disposition the $200 rule reaches. The payoff itself is not.
How the property is used changes the analysis. Under §988(e)(3), a "personal transaction" is any transaction by an individual except to the extent expenses properly allocable to it would qualify under IRC §162, other than travel expenses, or §212(1) or (2), meaning production of income or management of income-producing property but not expenses connected with taxes. Rev. Rul. 90-79 applied that test to a residence mortgage: no allocable expenses met §162 or §212, so §988 did not govern and pre-§988 principles controlled, under which the payoff was still a closed and taxable transaction. Put a tenant in the property and the calculus shifts: the mortgage carries §212 or §162 expenses, §988 applies on its own terms, and both gain and loss become ordinary and recognized. That is a real difference between an expat's home and a foreign rental property, worth settling before you sign the loan.
What Are Functional Currency and a Qualified Business Unit?
Your functional currency is the yardstick everything else is measured against, and for a US individual it is the dollar. IRC §985(b) makes the dollar the functional currency unless the taxpayer has a qualified business unit (QBU) operating in a foreign economic environment and keeping its books in another currency, which then becomes that QBU's functional currency. IRC §989(a) defines a QBU as any separate and clearly identified unit of a trade or business that maintains separate books and records.
Living, earning, and banking abroad do not change your functional currency. It stays the dollar, which is exactly why every foreign currency item must be translated and why currency movement becomes income at all. A QBU is a business concept, typically a foreign branch or disregarded entity, not something an expat acquires by moving overseas.
Which Exchange Rate Are You Required to Use?
The IRS has no official exchange rate. It generally accepts any posted exchange rate, provided the rate is used consistently. The yearly average table published on IRS.gov is a convenience that spares taxpayers from tracking daily rates on recurring income, not a mandate. Consistency matters more than the source: pick a defensible published rate, apply it the same way across the return and across years, and document it. Two points follow.
Spot rates govern discrete events. The mortgage computation above turns on two specific dates, not an annual average. Averages suit income earned ratably through the year, such as salary. They do not suit a single dated transaction like a loan payoff or a sale, a point worth pairing with the basis rules on selling foreign property.
FBAR follows a different rule. FinCEN directs FBAR filers to use the Treasury year-end rate for maximum account values on FinCEN Form 114. The same taxpayer, in the same year, can therefore legitimately use a chosen posted rate on the income tax return and the Treasury rate on the FBAR. That is not an inconsistency. It is two agencies with two instructions.
Does the Foreign Tax Credit Offset Currency Gain?
Usually not, because the country where the property sits does not tax the same item. It measures the mortgage in its own currency, where nothing happened: you borrowed €500,000 and repaid €500,000. The gain exists only because the US insists on a dollar yardstick, so there is no foreign tax on it to credit and the foreign tax credit on Form 1116 often provides no relief. Anyone planning a move abroad should price this in before financing a foreign purchase, since the timing of a payoff or refinance is one of the few variables still under the taxpayer's control.
Bottom Line
Exchange rate movement becomes income the moment a currency position closes, and under IRC §988 that income is ordinary. For most individuals the position they do not know they hold is a foreign currency mortgage: §988(c)(1)(B) treats becoming the obligor as a §988 transaction, and the day they pay, refinance, or sell, the position closes and is measured, under Reg. §1.988-2(b)(6) if the property is a rental or business asset, and under the pre-§988 rules of Rev. Rul. 90-79 if it is a personal residence. The gain is real even when no dollars move, the $200 de minimis does not reach it, and the offsetting loss on the property is generally unavailable when the property is personal.
Have questions about Section 988 foreign currency gains or a foreign mortgage payoff? Contact TS CPA for a free consultation. We respond within the same day.
Official IRS and Government Sources
- IRC Section 988, Treatment of Certain Foreign Currency Transactions
- Reg. Section 1.988-2, Recognition and Computation of Exchange Gain or Loss
- IRC Section 985, Functional Currency
- IRC Section 989, Other Definitions and Special Rules
- IRS Foreign Currency and Currency Exchange Rates
- IRS Yearly Average Currency Exchange Rates