APR
Annual percentage rate: the yearly cost of borrowing money, shown as a percentage. It is the number to compare on cards and loans.
APR is the yearly interest rate on debt. For loans, it can also include some fees, so it reflects the full cost better than the interest rate alone.
Credit cards usually charge interest daily. The card divides the APR by 365 to get a daily rate, then applies it to your balance each day. A card can have different APRs for purchases, balance transfers and cash advances. Paying your full statement balance by the due date usually means you pay no interest on purchases.
Example
A 24% APR is 24% ÷ 365 = about 0.0658% a day. On a $1,000 balance for 30 days, that is about $1,000 × 0.0658% × 30 = $19.73 in interest.