Different card issuers use different rules to determine when they begin charging interest and different methods to calculate interest. You should check with your card issuer for information on how interest is calculated for your account.

In general, most card issuers place different transactions into different categories, such as purchases and cash advances. For each category, the card issuer will use different periodic rates to calculate interest on each balance. For purchases there are often special rules creating a grace period during which no interest is charged if you pay the entire balance in full by the payment due date.