In love with your points-earning credit cards? Just make sure they aren’t costing you. Americans on the whole are getting worse about managing their credit card payments, and it is costing them dearly. A recent study estimates that Americans have paid more than $3 billion in credit card late fees since 2015. No annual fees. Not interest. Late fees.

The study by NerdWallet found that over a quarter of those holding a card made at least one payment that was late. Each instance typically costs $25 to $39, depending on your bank and the terms of the card. Most minimum payments are fairly small, so even if you cannot pay the balance in full (although you should be doing so), avoiding a late fee should be relatively easy.

Americans Like Earning Rewards

The high rewards offered by many credit card products are very enticing to the general consumer. The same study concluded that Americans prefer rewards over interest rates. The Market Watch commentary suggests that our “priorities are out of order”. I only agree if you’re paying interest each month. But paying interest completely defeats the purpose of using the card to earn rewards. If you’re not paying the bank a nickel in interest, who cares what the interest rate is?

But most should be caring. Over half of those with cards in the U.S. don’t pay them off in full every month.

To be successful in the award travel hobby, you have to be financially disciplined. I often give advice to people I know regarding rewards-earning credit cards, generally focusing on what the best options are for them and what some current great sign-up bonuses are being offered. But I’m always clear that it is a tool for you. If you don’t pay the balance off every month, it is a trap. Rewards don’t matter if you’re paying interest.

And I don’t even want to know how much Americans pay the banks each year in interest. I’m sure it is astounding.