The 7/10 Rule means that for every $1 to turn into $2 at a 10% rate of return, it takes 7.2 years. That results from dividing 72 by 10. Similarly, if you apply the formula to Warren Buffet’s number, $10,000 takes approximately 10 years (72 divided by 7) to double.   This is similar to the rule of 72, which is a rule that helps determine how long it will take your money to double, at a given yield or rate of return. Divide the rate of return by 72 to get the number of years until your investment doubles. With a five percent yield, it will take 14.4 years to double [72/5% = 14.4 years].