The Rule of 72

The Rule of 72 can be used to estimate the amount of time it will take for you to double your money at a given interest rate.

The formula is simple -- just divide the interest rate into 72.

For example, if you put your money into an account with 8% interest, it will take you 9 years to double your money (72 / 8 = 9).

Just a handy rule to keep in your pocket! =)