Nearly half of Americans don't know their credit card APR. Here's why that can cost you.

Almost half of Americans don't know how much their credit card debt could be costing them, a new survey shows. 

That's because more than 47% of Americans say they don't know their current credit card annual percentage rate (APR), which is its effective yearly interest rate, according to LendingClub, a financial services company. Being in the dark on how much interest your issuer charges can be costly, particularly if you carry a balance from month to month. 

A credit card's APR determines the cost of borrowing money, and only comes into play when a cardholder doesn't pay off their bill in full each month by determining how much interest they'll pay on the balance. Consumers collectively owe a record $1.14 trillion in credit card debt, while APRs have jumped due to the Federal Reserve's flurry of interest rate hikes, which have pushed rates to their highest point in 23 years.