For transactions in currencies different from your card’s currency, the transaction will be converted at the standard exchange rate set by the Mastercard payment system. You can find Mastercard currency exchange rates on the official website of this payment system.

 

When you make transactions in currencies other than your card's primary currency, it takes these transactions 2-3 days to settle. This is how Mastercard works. The whole process has 2 primary stages, pre-authorization (funds are blocked on the card), and final settlement (the amount is charged from the card). When the final settlement happens, the currency exchange rate for the day of settlement is used. It can technically be different from the exchange rate used for initial pre-authorization. Depending on how the exchange rate behaves during these 2-3 days, you may notice that the final charge is slightly more or less than the pre-authorization amount.