According to the information provided by Agricultural Bank of China, the annual interest rate of credit cards is 18.25%. According to the interest rate calculation formula, the overdraft amount is 300,000 times the annual interest rate 18.25%, and the annual interest is 54,750 yuan. This means that if the credit card overdraft limit is 300,000 yuan and it is not paid back within one year, the user will have to pay about 54,750 yuan in interest.