The threads mia pointed you to will answer your question, but there are a lot of wrong answers in there as well. The appropriate answer is that, while AMEX does print a "pay by" date that is roughly 2 weeks after the statement close date and the online pay by date is a few days later still, probably to account for the time it would take to be delivered to them by mail, you actually have until the next statement prints to pay your balance in full. If possible, however, I would pay by their recommended dates, as this likely pleases them.