For a constant growth rate of r%, the formula for the doubling time Td is given by log(2)/log(1 + r/100) which can be simplified to approximatly 70/r. * See ht

For a constant growth rate of r%, the formula for the doubling time Td is given by log(2)/log(1 + r/100) which can be simplified to approximatly 70/r. * See http://en.wikipedia.org/wiki/Rule_of_72 http://en.wikipedia.org/wiki/Rule_of_72 for more info and background/variations that improve on accuracy in certain situations.