Mental Math: Years to Double an Investment

Sharing a very simple, but handy mental math rule that was mentioned in quite a few of our MBA classes, such as Investment Styles and Strategies, Designing Financial Models that Work and others:

If you want to quickly ballpark the # of years it will approximately take for an investment to double, then just divide 72 by the annual growth rate. For example, if your investment grows 7% a year, it will take slightly more than 10 years for it to double (72/7). But if it grows 36% a year, it will only take about two years to double (72/36). 

You can read more about this “Rule of 72” on Wikipedia. Now, you now you can come across as a math genius without much effort 😉