Borrowing money requires interest, and credit card repayment does not require interest during the interest-free period. When banks issue credit cards, the main source of income is not only interest, but the handling fees paid by merchants who accept credit cards. When a consumer swipes a card at a merchant, the merchant must pay a bank handling fee of several thousandths to several percent and settle with the bank every month. It should be said that the bank gives a certain credit line according to the personal credit situation, which is used for the business of spending first and then repaying.