APR (Annual Percentage Rate) is the true annual cost of borrowing money. For credit cards, APR typically ranges from 17% to 29.99%. For car loans, 4%–15%. For student loans, 4%–13%.
To calculate monthly interest from APR: divide by 12. A 24% APR card charges 2% of your balance in interest each month. On a $5,000 balance, that's $100/mo in pure interest before any principal reduction.