On weekdays (Mon-Fri London time) the interbank exchange rate is applied to all transactions with exception to Thai Baht where there's a 1% markup on top of the interbank rate.
If you exchange currencies on weekdays (Mon-Fri UTC) you will receive the interbank exchange rate without any markup on all currencies except for Thai Baht where there's a 1% markup, with a small 0.5% fee for anything above US$6500 per month(After 12th August this limit will be changed; see our Fees page).
On the weekend (Sat-Sun London time) the provided rates are fixed to protect against fluctuations, this means there are markups of:
A flat markup of 1.5% for Premium/Metal plan users and 2.5% for Standard users is also applied on each card payment funded by a cryptocurrency balance regardless of the day of the week, in order to cover our costs for enabling the exchange.
Also, we strongly recommend that you always choose to pay in the local currency when abroad as some merchants will charge you in your base currency and then apply their own foreign exchange fees on top.