A purchase interest charge is the interest you pay on your credit card balance for purchases you made but didn’t pay in full by the end of the billing cycle in which those purchases were made. The purchase interest charge is based on your credit card’s annual percentage rate (APR) and the total balance on that card. Credit card companies charge interest on any balances that you dont pay by the due date each month. When you carry a balance from month to month, interest is accrued on a daily basis, based on whats called the Daily Periodic Rate (DPR). DPR is calculated by taking your credit cards APR and dividing it by 365, for all the days in the year. If you pay only the minimum payment on your credit card statement, you do get charged interest. The interest charged on your credit card is based on your card’s APR (Annual Percentage Rate). Different card issuers have different rules for determining when they charge interest, but in general, once a card issuer begins to charge interest, it will continue to do so until it receives your payment.