Multiply the balance by the monthly rate to find your current monthly interest payment. Remember that interest is always calculated on the principal not the monthly. Calculate the interest portion of the payment Formula 131.
Subtract the monthly interest payment from your total monthly payment.
L loan principal 5000 c periodic rate monthly in this example 0005 n term number of months in this example 60 P principal and interest payment 9666month. First convert your annual interest rate from a percentage into a decimal format by diving it by 100. T Time Periods involved. When you know the principal amount the rate and the time the amount of interest can be calculated by using the formula.