Rule of 69

Very similar to the rule of 72, a rule stating that an amount of money invested at r percent per period will double in 69/r (in percent) + .35 periods. For example, if you bought a share of ADR yielding an annual return of 25%, the investment will double in a little over three years. 69/25 + .35 = 2.76 + .35 = 3.11 years