When you invest money, you earn interest on your capital. In the next year, you earn interest on your capital and the interest you earned the year before. Now this principle applies to any type of investment, debt repayment and the effects of the inflation rate on your buying power. By using Einstein’s Rule of 72 we can now accurately determine how long it will take to double your money (or your debt) at a given interest rate. The rule is simple, divide the number 72 by the interest rate you are receiving (72/10=7.2), and you will find the number of years it will take to double your money. It is called the Rule of 72 because at 10% interest, the money will double every 7.2 years.