It depends on the amount and how long you let it sit. Last year, I paid my credit card bill twice (dumb mistake) – so I had a credit of around $180 the next month. I didn’t use that card for a while, and after a month or so they mailed me a check and zeroed out the balance. I think there’s some regulation that the credit card companies can’t keep a credit for longer than a month or two. If I had used the card that month, it would have just whittled down the balance, which would have been OK with me. But as it happened, I didn’t need to use the card to they sent me the check.