There are two important reasons why you should never carry a balance on a rewards card. First, rewards cards tend to carry higher interest rates (APRs) than non-rewards cards. So, carrying a balance over from month to month can get expensive, as those interest charges are added to your balance.
Second, those high interest charges can negate the rewards you are earning with the card. For example, if you earn 2% in cash back for a purchase, but are assessed interest on any unpaid balance, you’re losing money instead of saving money.