The final repayment date of the credit card of the Postal Savings Bank is the 20th day after the bill date. Bookkeeping date is 19 (fixed), that is,

Generate a bill of 9.2 1 and record the transactions during the period of 8.22-9.2 1. The final repayment date is the 20th day after 9.2 1, namely 10. 1 1.

Generate the bill 10.2 1 and record the transactions during the period of 9.22- 10.2 1, and the final repayment date is the 20th day after 10.2 1.

And so on.

Obviously, 9.2 1 on the billing date has the shortest interest-free period of 20 days (9.2 1 brush,1return), and 9.22 on the first day after the billing date has the longest interest-free period of 50 days (9.22 brush,/kloc-0). It should be noted that credit card consumption has an interest-free period, and cash withdrawal has no interest-free period.