Rule of 72

Extracted from PanzerGrenadier's blog :

I also learnt more about the Rule of 72 which is a quick rule-of-thumb to determine how long your investment (or debt) doubles at a given interest rate. If you could get a return of 10% per annum compounded, it would take you approximately 7.2 years (72 divided by 10) to double your investment. If you could get a return of 2% per annum, it would take you closer to 36 years (72 divided by 2) to double your money. An 8% difference translates into 28 plus years to double your money.

http://fivecentstencents.blogspot.com/2008/02/financial-freedom-revisiting-lessons.html