Originally Posted by mia
Bear in mind, however, that exchange rates are based on the date the transaction is processed, not the purchase date. It is easy to see the processing date on the Merrill+ statement, but American Express shows only one date and that is typically the purchase date. This makes precise matching of transactions difficult.
My friend who was in Japan recently confirmed this for me the other day. He graphed his purchases (all on his company Amex) against the interbank rates, and every purchase was almost exactly 2% above the interbank rate for the date the transaction POSTED, not the date of the purchase.