For consumption before 04, the account will be settled on 04, and the final repayment date is 20 days after the account is settled. So if you spend on the 4th, the interest-free period is the shortest, which is the 20th. For consumption after 04, the settlement and reconciliation will be conducted on the 4th of the following month, and the final repayment date will be the 20th day after reconciliation. So the money you spend on the 5th can be interest-free for up to 50 days.