If your bookkeeping date is 10 day per month, the 25th day after the bookkeeping date is the due repayment date; If you spend money in May 10, the due repayment date is May 25th, and the interest-free period is only 25 days (May10-May 25th); If you spend in July 1 1, the bill will be paid in August 10. Your final repayment date is September 5th, and the interest-free period is 56 days (July11-September 5th).