American Express uses the trailing interest method for the interest charged on a credit card. Trailing interest is the amount of interest that accrues between when a credit card bill is sent, and when payment is received. Also called "residual interest, " It applies only when you carry a balance on your credit card. Consumer advocates call it an unfair practice because unless you call your issuer and ask exactly how much it will cost to pay your bill in full on the date you expect your payment to arrive, you'll still owe interest on your next bill, regardless of whether you make any more purchases with your card. Most other credit card issuers will not charge you any interest if the full amount you owe is paid by the due date.