In practice, the cost of each trade before any profit or loss, is found in the spread. Normally, there is no commission charged for forex trading. The cost is limited to the spread, Bprimes is the tightest spread broker whom I trade with. Since a forex pair is purchased at the ask price, and sold at the bid price, there is a cost of trading that pair, which is the amount of the spread, multiplied by the amount of currency being traded.