In calculating simple interest P is the principal amount of cash invested at an interest fee R% per period for t, 5 Step Formula review Step Formula by David Humphries the variety of time periods. For these calculations the curiosity rate r is in decimal form, so observe that r is R% divided by 100. Simply take your interest price as a share and divide by 100. Also r and t are in the same items of time, sometimes years. Prt, the place I is curiosity, P is principal, r is interest rate as a decimal, and t is time interval. You then want so as to add the curiosity to the unique principal quantity to get the total interest plus principal. So doing it this way entails multiple steps. In case you wish to calculate only the easy interest quantity with out adding in principal use the CalculatorSoup&reg