A purchase rate is the interest rate that is charged on regular purchases that are put on a credit card. This is different from the cash advance rate, which is the interest rate that is charged on cash advances. The purchase rate is usually lower than the cash advance rate. This is because when you make a purchase, you are using your credit card to buy something that you will pay for in the future. When you take out a cash advance, you are borrowing money from your credit card company and will have to pay it back immediately.