When it comes to managing your credit card debt, you may be focused on the big picture — the balance due — but there is another number that you’d do well to pay attention to: It’s called the APR (annual percentage rate).

The annual percentage rate is the rate of the interest payments you’ll make over a 12-month period. The number is important because it will largely determine how much extra money you’ll be paying for keeping a balance on the account.

Study: 48% of credit card holders don’t know their APR

The thing is, nearly half (48%) of balance-carrying cardholders don’t even know their APRs, according to a new study from Creditcards.com.

The findings come from a survey of 2,315 Americans, including 1,681 of them with at least one credit card, who answered an online poll on whether they knew their APRs. While many people expressed a little knowledge about their APRs, one-third of them were absolutely clueless, Creditcards.com reports.

Wallet whiz Clark Howard says knowing your interest rate is the key to using a credit card effectively.

“If you know that you are a person who is not typically going to be able to pay off your balance in full each month, the most important thing to consider when you’re getting a new credit card is getting a card with the lowest possible interest rate,” he says. “A lot of credit unions have cards with really low rates — many in the single digits, under 10%. Most major issuers average around 17%.”

If you’re struggling with credit card debt, you may be wondering what you can do. Here are a couple ways to trim your bill:

2 ways to pay off your credit card bill

Transfer your balances: If you have more than one credit card, it may be feasible for you to transfer your credit card balances. Not only does this allow you to focus on one bill instead of multiples each month, it could allow you to score a lower APR. This would mean that more of your money could actually go toward the balance rather than to fees.

Pay more than the minimum due: If you can, try to pay more than just the minimum amount due on your credit card bill. Clark says, “That will allow you to eliminate the debt faster, save money on interest — and most importantly, stay motivated to get the job done and behind you!”

Speaking of motivation, if you want to join thousands of others on a journey to being debt-free, become a member of Clark’s Ditch Your Debt Facebook group. Not only will you learn real-world savings tips, but you’ll find supporters that can cheer you on to financial success.

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