When your 0% intro APR promotional period ends, your account APR will change to its regular APR, which was set when your account was opened. This may be a variable APR that takes into account your creditworthiness, or it may be a fixed APR. If you pay off your balance in full every month, you’ll continue to be able to use the card interest-free. But if you carry a balance from month to month, you’ll pay interest on that balance.