Given that most credit cards with 0% intro APR don't come with annual fees, it's not necessary to close the card when the introductory period ends. In fact, closing it could lower your credit score. Your credit utilization ratio -- that is, your overall debt divided by your overall credit limit -- plays a large part in calculating your credit score. The lower it is, the better. By keeping your credit card open after the 0% intro APR ends, and also not running up a balance, you'll be keeping your debt-to-credit ratio low. However, the key is not to run up a balance. If you can't trust yourself to keep the card open without falling into debt, it's best to close the card and remove the temptation.