example: the 1th day of each month is the billing date of an agricultural bank card, and the 25th day after the billing date is the due repayment date. If the customer spends money on the 1th of a month, the interest-free repayment period of the customer is 25 days; If the customer spends money on the 9th of a month, the interest-free repayment period of the customer is 26 days; If customers spend money on the 11th of a month and the interest-free repayment period is the due repayment date of next month, they can enjoy the interest-free repayment period of 56 days.