How Long to Double Your Money?

How can you find out how long it will take to double your money when you invest it at a certain interest rate? It's simple, really, thanks to what investment types call the 72 rule. The 72 rule simply states that, to find out how long in years it takes to double a nest egg, just divide the interest rate by 72. For instance, if you have money invested at 10% it will double in 7.2 years (10/72). If it was earning 8%, it would take 9 years to double.