If you want to enjoy the longest interest-free period as possible, you can spread the billing dates of the four credit cards. Whenever you make a purchase in the future, choose the credit card with the billing date that just passed, so that each transaction All purchases enjoy a longer interest-free period to the maximum extent. For example, the billing dates of the four credit cards are adjusted to 1, 8, 15, and 22nd, and the repayment date cannot be chosen arbitrarily and can only be determined based on the billing date.