Your friend's credit card is used on the second day of the billing date, with the longest interest-free period. You'd better master this principle. For example, the credit card of Bank of Communications, today's billing date is 5. 12, and it will be spent tomorrow. The billing date is next month 12. The longest interest-free period of Bank of Communications credit card is 56 days, and it can be repaid before July 7. So are other credit cards. If you have any questions, please keep asking.