Exchange Rates, Spreads and Fees: What a Currency Conversion Really Costs

An exchange rate is a price: the number of units of one currency that a single unit of another will buy. A quote of 1.0850 USD per EUR means one euro costs $1.085. Any conversion you pay for involves two things, the rate you are given and the fees charged around it, and the only reliable way to judge either is to hold it up against a neutral benchmark. Every rate used in the examples below is an example rate stated in the text, chosen to make the arithmetic clear. None of them is a current market price.

Where the Benchmark Rate Comes From

Currencies are traded over the counter between banks, funds and companies, not on a single exchange. The market is enormous. The Bank for International Settlements' 2025 Triennial Survey measured turnover of $9.6 trillion per day in April 2025, up 28% from 2022, and found the US dollar on one side of 89% of all trades. With thousands of dealers quoting at once there is no single official price at any instant, only a band between bids (what dealers will pay) and offers (what they will charge). The midpoint of that band is called the mid-market rate.

The European Central Bank turns that moving market into one daily snapshot. Its euro reference rates are based on a concertation procedure between central banks that normally takes place around 14:10 CET, and they are usually published around 16:00 CET on each working day except TARGET closing days. The ECB says the rates are for information purposes only and discourages using them for transactions. That restriction is what makes them a good yardstick: nobody earns a margin on them.

The Currency Converter loads these ECB figures when the page opens and labels the result with their publication date. Because each published rate is expressed against the euro, any other pair has to be built as a cross rate: the target currency's euro rate divided by the source currency's euro rate.

Example 1: A Cross Rate and a Bank's Margin

Marta, a translator in Manchester, invoices a client in Ohio for $4,200. On the day the money lands, suppose the reference table lists 1.0850 US dollars and 0.8420 pounds per euro. Her bank converts the payment into sterling at 0.7600 pounds per dollar and shows no fee.

1. Cross rate from dollars to pounds: 0.8420 ÷ 1.0850 = 0.776037, or 0.7760 rounded to four places.
2. Value of the invoice at the reference rate: 4,200 × 0.776037 = £3,259.35.
3. Amount the bank actually credits: 4,200 × 0.7600 = £3,192.00.
4. Shortfall: £3,259.35 − £3,192.00 = £67.35.
5. Margin as a share of the reference rate: (0.776037 − 0.7600) ÷ 0.776037 = 2.07%.

The bank charged nothing that it called a fee, yet Marta paid £67.35 for the conversion. A margin built into the rate is still a charge; it is simply harder to see on a statement. Type the bank's rate into the optional rate field of the converter to see the credited amount, and use the Percentage Decrease mode of the Percentage Calculator with the reference rate and the offered rate to express the gap as a percentage. That percentage is the number to compare between providers, because it does not depend on the size of the payment.

What Moves Exchange Rates

The benchmark itself changes every day, for reasons that are easier to name than to forecast.

Interest rates

Money tends to flow toward currencies that pay a higher return on deposits and bonds. When a central bank raises its policy rate, or markets start to expect it will, buying interest in that currency usually rises; an expected cut has the reverse effect. Much of a typical day's movement is markets revising those expectations after new data or a central bank statement.

Inflation and purchasing power

If prices rise faster in one country than in another, each unit of its currency buys fewer goods at home, and over long periods its exchange rate tends to drift down against currencies with steadier prices. The link is loose over months and clearer over years.

Trade and capital flows

An exporter that sells abroad has to convert its foreign earnings into its home currency, and an investor buying foreign shares has to buy the foreign currency first. Shifts in those flows, along with risk sentiment during political or financial stress, push rates in both directions.

Pegs and bands

Some currencies are not left to float. Hong Kong's Linked Exchange Rate System has operated since 17 October 1983 and keeps the Hong Kong dollar within a band of HK$7.75 to HK$7.85 per US dollar. Under a peg like this, the authority stands ready to buy or sell its currency at the edges of the band, so the market rate moves only inside it.

Example 2: A Hotel Bill Paid by Card

Tom, from Boston, checks out of a hotel in Lisbon with a bill of €640. Take the reference rate that day to be 1.0850 USD per EUR. His card issuer adds a 3% foreign transaction fee. The card terminal also offers to charge him in dollars at 1.1425 USD per EUR, an option known as dynamic currency conversion.

1. Bill at the reference rate: 640 × 1.0850 = $694.40.
2. Card fee on a payment in euros: 3% of $694.40 = $20.83, so his card is charged $694.40 + $20.83 = $715.23.
3. Paid in dollars through the terminal: 640 × 1.1425 = $731.20.
4. Terminal rate compared with the reference: ($731.20 − $694.40) ÷ $694.40 = 5.3% more.
5. Extra cost of accepting the terminal's offer instead of paying in euros: $731.20 − $715.23 = $15.97.

Even with a card that charges a foreign transaction fee, paying in the local currency came out cheaper here, because the rate offered at the terminal was set by the merchant's payment provider rather than by Tom's card network. A card without a foreign transaction fee would have brought the charge close to $694.40. The Percentage Calculator handles both steps: its Percentage Of mode gives the 3% fee, and its Percentage Increase mode measures how far the terminal's price sits above the reference value.

Example 3: Sending Money Abroad

Ana lives in Houston and sends $1,500 to her mother in Mexico City. She compares two transfer services against an example reference rate of 19.20 Mexican pesos per US dollar, at which her $1,500 would be worth MX$28,800.00.

	Service A	Service B
Exchange rate offered	18.62	18.95
Transfer fee	$4.99	$12.00
Total Ana pays	$1,504.99	$1,512.00
Her mother receives	MX$27,930.00	MX$28,425.00
Rate below the reference	3.02%	1.3%

The steps are the same for each column. The amount received is 1,500 multiplied by the offered rate, and the margin is the reference rate minus the offered rate, divided by the reference rate. Service A advertises the smaller fee, but its weaker rate delivers MX$495.00 less. At the reference rate those pesos are worth $25.78, against a fee difference of only $7.01, so Service B is the better deal despite its higher headline fee.

For transfers sent from the United States, federal rules make this comparison easier. Under 12 CFR § 1005.31, a remittance transfer provider has to show the sender, before payment, the transfer amount, the fees and taxes it imposes, the total, and the exchange rate it will use, rounded to between two and four decimal places. Under § 1005.34, a sender who asks to cancel no later than 30 minutes after paying is generally entitled to a refund, provided the funds have not yet been picked up or deposited. Put that disclosed rate into the Currency Converter next to the reference figure before you confirm the transfer.

Taxes, Crypto and Other Conversions

Currency is often only one layer of a foreign price. A shop in the euro area that lists a jacket at €238.00 including 19% VAT is charging €200.00 for the jacket and €38.00 in tax. The VAT Calculator separates the two in its remove mode by dividing by 1.19, which is not the same as taking 19% off the gross price. Whether the tax still applies to a buyer outside the country depends on that country's rules for exports and on the import taxes at the destination, so convert the net and gross amounts separately and confirm which one you will actually pay.

Cryptocurrencies are absent from the ECB's reference list, and their prices change from minute to minute, so the Crypto Converter does not load a price feed at all. It converts using prices you enter, such as the ones shown on the exchange you plan to use, and the same discipline applies: compare the price you are quoted with an independent one and treat the difference as a cost.

Reading Any Currency Quote

• Find the date of the benchmark. ECB figures are published once per working day, so on a weekend or a TARGET holiday the latest table can be two or three days old. A provider's live quote can legitimately differ from it by a small amount for that reason alone.
• Convert the margin into a percentage. Divide the gap between the reference rate and the offered rate by the reference rate. That is the figure to compare between a bank, a card and a transfer service, since a fee in currency units depends on the amount sent.
• Add the fixed fees back in. As Ana's comparison shows, the provider with the lowest fee is not always the cheapest. Compare what arrives against what leaves your account.
• Check which direction the quote runs. 0.7760 pounds per dollar and 1.2886 dollars per pound describe almost the same rate. Mixing up the direction is the most common reason a manual calculation goes badly wrong.
• Pay in the local currency at a card terminal. In Tom's case the terminal's rate was 5.3% above the reference, more than his card's own fee.