We use the exchange rate of the day that the payment is settled.
At that moment, we charge the FX fee, which is 1.2% for the primary settlement currencies (EUR, USD, GBP, SEK, NOK, etc) and 3% for other currencies. We use the daily midday rate from Oanda plus the markup.
You can also retrieve daily currency and exchange rate information for all supported currencies in the Exchange rate report. To retrieve this report, go to the Customer Area > Finance > Under downloadable report click Exchange rate.