To calculate simple interest in Excel (i.e. interest that is not compounded), you can use a formula that multiples principal, rate, and term. This example assumes that $1000 is invested for 10 years at an annual interest rate of 5%. Simple interest means that interest payments are not compounded – the interest is applied to the principal only. Using the function PMT(rate,NPER,PV) =PMT(17%/12,2*12,5400) the result is a monthly payment of $266.99 to pay the debt off in two years. The rate argument is the interest rate per period for the loan. For example, in this formula the 17% annual interest rate is divided by 12, the number of months in a year. To calculate simple interest in Excel (i.e. interest that is not compounded), you can use a formula that multiples principal, rate, and term. This example assumes that $1000 is invested for 10 years at an annual interest rate of 5%.