Dated exchange rates allow you to map a currency conversion rate to a specific date range. For example, the exchange rate on January 1 was 1 USD to 1. 39 AUD, but on February 1, it changed to 1 USD to 1. 42 AUD. Your opportunities that closed between January 1 and February 1 use the first exchange rate (1 = 1. 39), while opportunities that closed after February 1 used the second exchange rate (1 = 1. 42).