Dynamic currency conversion sounds neutral. In practice it is one of the more expensive choices you can accidentally make on a trip. Understanding it makes future decisions automatic.

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When you pay by card in a foreign country, the terminal often asks whether you want to be charged in the local currency or in your home currency. The home-currency option looks helpful. It is not.

Choosing home currency at the terminal hands conversion control to the merchant's processor. The rate applied is typically three to seven percent worse than the network rate your card would use if you chose local currency.

The reason it exists at all is that the merchant and processor share the markup. That is why the terminal politely defaults to home currency in many countries.

The rule is simple. Always choose local currency. Your card network handles conversion at close to the mid-market rate, and any foreign transaction fee your issuer charges is a separate line you can see.

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One warning worth remembering: some terminals hide the choice behind confusing UI. If in doubt, ask the cashier which currency the charge will be in. If they cannot tell you, cancel and try again on a different terminal or with cash.