Effective annual interest rate calculation. The effective annual interest rate is equal to 1 plus the nominal interest rate in percent divided by the number of compounding persiods per year n, to the power of n, minus 1. Effective Rate = (1 + Nominal Rate / n) n - 1. Example. What is the effective annual interest rate for nominal annual interest rate of 5% compounded monthly? Solution: Effective Rate = (1 + 5% / 12) 12 - 1 = (1 + 0.05 / 12) 12 - 1 = 0.05116 = 5.116% If your borrowed total is $50,000, for example, and you have two points, your effective sum will be $51,000 and this figure is what you will make monthly payments based on. In response, these two theoretical points serve to drive up the annual interest rate to an actual interest rate, points inclusive. The Effective Annual Rate (EAR) is the interest rate that is adjusted for compounding over a given period. Simply put, the effective annual interest rate is the rate of interest that an investor can earn (or pay) in a year after taking into consideration compounding.