Annual percentage rate example. When shopping for a mortgage, the borrower should understand that APR is an annualized interest rate that is calculated by taking the base interest rate and adding Interest rate The monthly effective interest rate. For example, the periodic rate on a credit card with an 18% annual percentage rate is 1.5% per month. Interest Rate The percentage of the value of a balance or debt that one pays or is paid each time period. For example, if one holds a bond with a face value of $1,000 and a 3% interest rate payable each The Effective Annual Rate (EAR) is the rate of interest actually earned on an investment or paid on a loan as a result of compounding the interest over a given period of time. It is higher than the nominal rate and used to calculate annual interest with different compounding periods - weekly, monthly, yearly, etc.