The Rule of 72 is a very simple concept. It is every library in the world yet most people never learn it. If you have a credit card or a savings account, it is at work in your life whether you know the rule or not.

It works like this: Take the interest rate that you are getting and divide it into 72. This will give you the numbers of years that it will take your money to double.

Here is an example:
Lets say you have a Certificate of Deposit at your local bank. You are getting an interest rate of 3%. 72 divided by 3 is equal to 24. If you have $1000 in the CD, it would double to $2000 in 24 years.
Now if you were getting an interest rate of 12%: 72/12 = 6. That means that your money would double in 6 years. In the same 24 year time span as the previous exmaple your money would double four times. That means your original $1000 investment would be worth $8000.
Which one would you prefer?