Compound Interest and the rule of 72

The rule of 72 is like a math formula. It helps to determine how long an investment takes to double. When I say the rule of 72 is like a math formula, is because investors divide 72 an amount of years to get an estimate of how many years it will take for the initial investment to duplicate itself. Interest which is calculated not only on the initial principal but also the accumulated interest of prior periods.

By using a compound interest calculator, we make money not only out of our initial amount of money, but also on the interest we made the first time. It sounds a little confusing but it is not.
Well I'm going to try to explain it in easier words. Let say I invest 100.00 dollars and the interest rate is 10% in one year I will make 200.00 dollars. The second year my interest rate of 10% will apply on the 200.00 dollars not on my initial amount of money.