Taxes and currency conversion basics

This is general information, not tax advice. Tax rules differ by country, by type of income and sometimes by year, and they change. The aim here is to explain the thinking behind the rate question so you can ask your accountant or tax authority sharper questions.

The problem is simple to state. You earn, spend or hold money in one currency, and your tax return wants a single figure in another. Somebody has to pick the exchange rate. That choice can move your taxable total up or down, usually by a modest amount, occasionally by a lot.

The principle most tax authorities share

Strip away the national detail and you tend to find three ideas.

First, the rate should reflect the date the money arose. Not the day you did your bookkeeping, and not the day you filed. If a client paid you in the middle of March, March is the date that matters.

Second, you’ll often be allowed a reasonable alternative, such as an average rate across a month or year, where the payments were spread out. One average is simply less work than three hundred separate conversions.

Third, whichever method you pick, use it consistently, and keep evidence of where the rate came from. Switching methods each year because one happens to give a lower number is the sort of thing that attracts questions.

Those ideas are common, but they are not universal, and a rule that suits one tax type may not suit another. Each country has its own wording, and some pick the rate for you. The next sections show three official examples. They’re snapshots from November 2026, not a full rulebook.

Example: HMRC in the UK

HMRC’s guidance splits between companies and individuals, so it helps to take them separately.

For companies, HMRC’s Corporate Finance Manual says that for direct taxes its staff will generally accept the exchange rate a company uses in preparing its accounts, provided it uses that rate consistently. It adds that the London closing rate has no official or privileged status, that HMRC publishes monthly rates (the ones used for VAT) and annual averages and closing rates for certain dates, and that staff should not reject averages from a major international bank or a well-accredited financial website without good reason. It also says rates from general internet sites usually aren’t London closing rates.

For individuals, the Self Assessment foreign notes (SA106) say that to convert income to pounds you use the exchange rate at the time the income arose, and point to HMRC’s published yearly rates if you’re unsure. The notes don’t say whether that published figure counts as an average or a spot rate, so check the page itself, or ask an adviser, before leaning on it.

If you invoice in euros, our EUR to GBP page shows a current mid-market reference. That isn’t a tax rate, and HMRC’s published figures are separate.

Example: the IRS in the United States

On its yearly average exchange rates page, the IRS says US taxpayers must report in US dollars and that, “in general”, you should use the exchange rate prevailing, which it calls the spot rate, when you receive, pay or accrue the item. It carves out an exception for certain qualified business units, which can generally use the currency of a foreign country.

It also says it has no official exchange rate and “generally, it accepts any posted exchange rate that is used consistently.” The same page publishes a table of yearly average rates. It doesn’t spell out, on that page, exactly when you should prefer an average over the spot rate, so anyone choosing between the two should ask their preparer instead of guessing. And one more line from the page is easy to miss: the rates there don’t apply when paying US tax to the IRS. If the IRS receives a tax payment in foreign currency, it converts using the date the processing bank converts it.

Example: Canada, the CRA and the Bank of Canada

On its guidance for foreign employment income, the CRA says to report in Canadian dollars, converting with the Bank of Canada exchange rate in effect on the day the amount arises. If you received payments at different times during the year, the page recommends the Bank of Canada’s annual average rate. It also says the CRA may accept rates from other providers if they meet certain conditions listed on that page.

Meanwhile the Bank of Canada describes its own daily exchange rates as indicative only, built from averages of aggregated price quotes from financial institutions, and published once each business day. Each is expressed as the Canadian dollar value of one unit of the foreign currency. If you convert dollars regularly, the USD to CAD page will show you the direction of the pair, but it won’t stand in for the tax authority’s table.

Note the family resemblance, and note what none of them promise: that any one rate is the only correct one. Day-of rate as the default, an average where payments are scattered, and documentation always. Three different agencies, one shape.

A worked example with a made-up freelancer

All figures are illustrative. Say a made-up freelancer called Dana invoices a US client $1,000 three times in a year, and her home currency is the Indian rupee. The rates on the payment days are 86.00, 88.00 and 92.00 rupees per dollar, and the year’s average is 88.50. (These numbers are invented, so don’t treat them as real rates for any year.)

Here the difference is 500 INR. In this example the method barely matters, because the rates rose and fell around the average. In a year where a currency moved sharply in one direction and most of the payments came late, the gap would be wider, which is exactly why authorities ask for consistency.

There’s a third number that isn’t either of those: what Dana’s bank actually credited after its own rate and fees. That money is real, but it isn’t necessarily what your tax authority wants you to record as income. Whether the difference counts as a cost, a loss or something else is a question for her tax adviser. Keep the bank statement, the invoice and a note of the rate source side by side.

Practical habits that make this easier

• Record the date, the amount in the original currency and the rate used for every foreign transaction at the time, not at year-end.
• Name the source of each rate (tax authority table, central bank, your bank) and save a copy or screenshot, since pages get updated.
• Pick one method, write down why, and use it every time the same kind of item comes up.
• If you hold foreign accounts or assets, ask whether separate reporting rules apply; the rate to use there can differ from income rules.
• Ask before you file if your income is large, volatile or in a currency with several official rates.

Our converter can show you roughly where a pair traded, with rates refreshed hourly, and the rate grid lays many pairs out together. For anything that goes on a return, though, use the table or method your tax authority or adviser names. A convenient number and an accepted number are different things.

Sources

• Yearly Average Currency Exchange Rates, Internal Revenue Service
• CFM12070: exchange rates used in company accounts, HMRC internal manual
• Foreign notes, tax year 2025 to 2026 (SA106), GOV.UK
• Line 10400 Other employment income, Canada Revenue Agency
• Daily exchange rates, Bank of Canada

Checked: November 2026