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 , I = Prt, therefore we have:A = P + I = P + (Prt), and finallyA = P(1 + rt)*.Calculate Total Amount Accrued (Principal + Interest), solve for A*.A = P(1 + rt)*.Calculate Principal Amount, solve forP*.P = A / (1 + rt)*.Calculate rate of interest in decimal, solve for r*.r = (1/t)(A/P - 1)*.Calculate rate of interest in percent*.R = r * 100*.Calculate time, solve for t*.t = (1/r)(A/P - 1)

Interests are calculated based on the rate of return on Investment (ROI). There are two methods that can be used on the Interest Calculator:

1. Simple Interest
2. Compound Interest

The Simple Interest is calculated using the following formula to find A, the Final Investment Value: 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.

According to ecalculatorsite.com the annual compound interest, including principal sum, is:
A = P (1 + r/n) (nt)

Where:

A = the future value of the investment/loan, including interest
P = the principal investment amount (the initial deposit or loan amount)
r = the annual interest rate (decimal)
n = the number of times that interest is compounded per year
t = the number of years the money is invested or borrowed