To convert to the currency of your credit card RCL will use retail market rate on the day of the transaction (end of cruise) and then add a service charge of 3%. Check your credit card policy for foreign exchange charges and fees. They will usually be less than the 3%. Least expensive way is to get a credit card in USD. You have to do the foreign exchange at some point and the best rate is usually done through online banking from your home currency to a USD account and then pay the USD cred