Why Your Card Charged a Different Rate Than You Calculated
Two things commonly explain the gap: a foreign transaction fee added by your card issuer (typically 1–3%), and dynamic currency conversion — a merchant choosing to charge your card in your home currency using their own, usually less favorable, exchange rate instead of letting your card network handle the conversion.
A card statement showing a worse rate than a currency converter calculated isn't a mistake on either side — it's almost always one of two specific, identifiable causes.
Foreign transaction fees
Many cards add a flat percentage fee — commonly 1–3% — to every purchase made in a foreign currency, on top of whatever exchange rate is applied. This fee is usually disclosed in a card's terms but easy to overlook, and it's a fixed cost of using that specific card abroad rather than something that varies with the transaction.
Dynamic currency conversion at the point of sale
When paying abroad, some merchants or ATMs offer to charge the transaction in your home currency instead of the local one — this is called dynamic currency conversion. It sounds convenient, but the exchange rate the merchant applies for that conversion is typically worse than what your card network would use if the transaction were processed in the local currency instead.
The practical fix is straightforward: when given the choice at a terminal or ATM, choosing to be charged in the local currency (declining the conversion offer) generally results in a better effective rate.
Timing differences
Exchange rates move continuously, and a card transaction is often processed and posted a day or more after the purchase — the rate applied is typically the rate at processing time, not the moment of purchase, which can account for a small additional difference from whatever rate a converter showed at checkout.