The Rule of 72

The 'Rule of 72' is a simple way to calculate the number of years to double your money : divide 72 by your annual returns and the number of years it takes your money to double follows.

So, if you expect an annual return of 12%, it takes 6 years to double your money (72 / 12 = 6). You can also calculate the 'required return': Divide 72 by the number of years. If you have 10 years to double your money, you need 72 /10 = 7.2%. Only 5 years? Your required annual return would be 72 /5 = 14.4.