Generally, when we talk about credit card interest, we mean the purchase interest rate, which is the interest charged on purchases you make with your credit card.
If you don’t pay your full balance each month (or even if you pay the minimum amount), you are charged interest on all the outstanding transactions and the remaining balance. However, interest is also charged on cash advances, balance transfers, special rate offers and, in some cases, even the fees charged by the company.
The interest rate can vary, depending on the credit card. Some have an interest-free period, otherwise you start paying interest from the day you make a purchase or from the day your monthly statement is issued. So avoid interest by paying the full amount promptly.