The credit card is paid in installments of 12 yuan, divided into 12 installments, with a fixed monthly repayment of 17.2 and a nominal annual interest rate of 7.2%. How to convert the actual annual interest rate, please find a specific formula. The actual interest rate is the time cost of the money you actually paid. The first period is 17.2 yuan, which is 17.2*7.2*11/12 earlier than the actual interest rate, which is equivalent to paying 17.2 * 7.2 * 1/12 in the second month ... and so on, it will be 17.2 * 7.2 in November. Then 72 plus the overpaid interest is the actual interest, and the actual interest is divided by 12 to get the actual interest rate.