Exchange rates change from minute to minute and banks use different rates when converting to or from your local currency. Credit card companies also may add a percentage to the market rate.
This calculator uses the same rate for conversions both to and from each currency and are updated once a day. The results given by the converter are only intended to be indicative and can be several percentage points different from the rate actually used to charge your card account.
On very large purchases where the exchange rate difference could be significant please check with your bank.