works credit cards. a better understanding of this alone can mean money saved off your annual interest bill.
most people assume that this period starts from the date of the purchase. this is not correct. the interest free period starts from the beginning of your statement period (you can find the statement period at the top of your most recent credit card statement).
a statement period is usually 30 days ? so if you have a 55 day interest free period on your card, you will have an extra 25 days from the end of your statement period to pay the full balance before interest is charged (that is a total of 