Rule of 72 Calculator
Instantly find how long it takes your money to double at any rate of return.
A mental-math shortcut
Divide 72 by your annual return to estimate the years it takes an investment to double. At 12%, that is 6 years; at 8%, 9 years. It is remarkably accurate for typical rates.
The math
The exact doubling time is ln(2) ÷ ln(1 + rate). The Rule of 72 approximates this closely for rates between 4% and 15%.
Frequently asked questions
How accurate is it?
Very, for rates from ~4% to 15%. At higher rates the exact figure diverges slightly — this tool shows both.