calculate interest apr monthly example
Step 2. Divide the annual interest rate expressed as a percentage by 12 to calculate the monthly interest rate expressed as a percentage. For example, if you have an annual interest rate of 7.8 percent, divide 7.8 by 12 to find the monthly interest rate is .65 percent.Related Reading: Interest Rate vs. APR Rate.anks accounts and loans often state the annual interest rate, but compound interest on a monthly basis, meaning that you need to know the monthly rate to calculate how much interest you will earn have to pay.