how to compute interest rate
Simple Interest Formulas and Calculations: Use this simple interest calculator to find A, the Final Investment Value, using the simple interest formula: A = P(1 + rt) where P is the Principal amount of money to be invested at an Interest Rate R% per period for t Number of Time Periods. Where r is in decimal form; r=R/100; r and t are in the same units of time. The accrued amount of an investment is the original principal P plus the accumulated simple interest, I = Prt, therefore we have: A = P + I = P + (Prt), and finally A = P(1 + rt). 1  Calculate Total Amount Accrued (Principal + Interest).