The Rule of 72 | Curiwise

1 / 7

Hook

Doubling, in your head

Someone offers you 8% a year on your savings. Quick — without a calculator — how long until your money doubles? You could wrestle with exponents and logarithms... or you could just divide 72 by 8 and say 'about 9 years.' That's the Rule of 72: one of the most useful mental shortcuts in all of money math.

Years to double ≈ 72 ÷ (the interest rate written as a plain number, like 8 for 8%).

Loading…