The Annual Percentage Rate (APR) is the interest rate for a year's worth of deposits. Interest rate is the ratio of the amount of interest to the principal amount of the deposit or loan for a certain period of time. There are three types of interest rates: the annual interest rate, the monthly interest rate, and the daily interest rate. The annual interest rate is expressed as a few percent of the principal, the monthly interest rate as a few thousandths, and the daily interest rate as a few ten thousandths.