...charging the interest rate? I have Chase and Capital One.

I also have a Capital One Master Card and have had it for 3 - 4 years or so. Like any other credit card I have ever had, you have 25 days to pay off whatever was charged during the billing period covered by your statement. If you pay off the balance in full, no interest is charged. After that the current interest rate is charged.

This Cap One card has really been great. In the second year I had it I received some cap one loan checks from them that you could fill out and deposit (or spend) for an instant loan at 3.9%. I still owed a bank about $8,000 that I had taken out on a college loan with an 8% interest rate. So I filled out one of the checks for $8,000 and deposited it in my bank, then sent the bank that I owed the $8,000 to a check for this amount, thus paying it off. So this effectively lowered my interest rate on that loan by more than half.

When you first apply for a credit card, they may offer a 0% interest for the first year - 18 months. However after this "starter" period credit companies charge interest each month.