What is the difference between APR and interest rate on a car loan?

The interest rate is the cost of borrowing the principal, while the APR (annual percentage rate) includes the interest rate plus certain finance charges, expressed as a yearly rate. On many auto loans the two are close or identical, but if a lender rolls in fees, the APR will be higher. The federal Truth in Lending Act requires lenders to disclose the APR, so use it to compare offers from different lenders on an apples-to-apples basis.