The interest-bearing method of Bank of Communications credit card is to settle interest on a daily basis. If your credit card limit is 30,000 yuan and you don't repay it in time after using it, the daily interest rate is 30,000 yuan × 0.0005 (daily interest rate) = 15 yuan according to the current interest rate of Bank of Communications credit card. If your billing cycle is 30 days, the monthly interest is: 15 yuan/day × 30 days = 450 yuan.

If the interest of Bank of Communications' credit card is fully paid off before the bill repayment date, there will be no interest expense. It is recommended that you pay attention to the repayment date when using credit cards to avoid unnecessary interest expenses.