Currency prices are constantly moving, so the trader may decide to hold the position overnight. The broker will rollover the position, resulting in a credit or debit based on the interest rate differential between the Eurozone and the U.S. If the Eurozone has an interest rate of 4% and the U.S. has an interest rate of 3%, the trader owns the higher interest rate currency because they bought EUR. Therefore, at rollover, the trader should receive a small credit. If the EUR interest rate was lower than the USD rate then the trader would be debited at rollover.