I think you're asking what happens if you have a negative balance on your credit card, like when you pay $600 on a $500 credit card bill. You would not receive any benefit or interest on that extra $100 you paid. Rather, it would just be used to cover your next $100 worth of charges you make with the card. So to answer your question, credit card accounts do not function like savings accounts. The credit card company will never offer you interest on negative balances.