Tools / Rule of 72

Rule of 72 · time in the market

How fast does money double?

Divide 72 by the yearly return and you get, roughly, the number of years it takes to double. The number of doublings you live through matters far more than the rate itself.

Inputs example

Doubles every–
Doublings in your time–
Cost of waiting–

The doubling staircase

One dollar, doubled

Start now or wait?

Start nowStart after waiting

How this works

The rule of 72 is a shortcut for the exact doubling time, ln(2) ÷ ln(1 + r). It is very close for returns between about 4% and 12%; the calculator shows both.

Doublings stack. At 8% a year money doubles about every 9 years, so 36 years gives four doublings: 1 becomes 2, 4, 8, then 16. The last doubling adds as much as all the earlier ones put together, which is why the final years of a long holding period count for so much.

Waiting is costly for the same reason. Starting five years late does not cut five years from the start of the curve; it cuts them from the end, where the biggest steps are. The rates here are steady examples, not predictions of what markets will return.