The rates are not set by your bank, but by your card issuer, e.g. VISA. However it's not the exchange rate differing, it's that they have different exchange rat

The rates are not set by your bank, but by your card issuer, e.g. VISA. However it's not the exchange rate differing, it's that they have different exchange rates for charges vs refunds. When a currency exchange happens, say from EUR to USD, it has a different exchange rate from USD to EUR. When the retailer 'refunds' you, the transaction isn't just cancelled or reversed, you are credited the amount of the original charge (in the retailer's currency), so there is a different exchange rate. For example, on the VISA Europe [0] site you can see the exchange rate for EUR to USD yesterday was 1 EUR = 1.11661 USD, but the other way around it is 1 EUR = 1.12399 USD. [0] https://www.visaeurope.com/making-payments/exchange-rates https://www.visaeurope.com/making-payments/exchange-rates