Free & private

Rule of 72 Calculator

Find out how many years it takes to double your money at a given rate of return using the classic Rule of 72, then compare it to the exact compounding answer.

Your numbers

Solve from a rate, or work backward from a target.

% / yr
×2Your result will appear hereEnter a rate or a target number of years, then select calculate.
Years to double
0.0

The Rule of 72 is a mental-math shortcut: divide 72 by the rate to estimate doubling time. The exact answer uses ln(2) ÷ ln(1 + rate), which is the true compound-growth solution.

How to use the Rule of 72 calculator

This free calculator runs entirely in your browser, so your numbers are never uploaded or stored. Pick whether you want to solve from a rate or from a target doubling time, enter your number, and select calculate.

1. Choose a direction

Solve years-to-double from a rate, or solve the required rate from a target number of years.

2. Enter your number

Use an expected annual return, savings rate, or growth rate for your scenario.

3. Compare estimate vs. exact

See the quick Rule of 72 estimate next to the precise compounding answer.

Understanding the Rule of 72

The Rule of 72 is a famous shortcut for estimating compound growth without a calculator: divide 72 by your annual rate of return to get roughly how many years it takes an investment to double. It works because of the mathematics of compounding, and it stays reasonably accurate for rates in the high single digits to low double digits.

The shortcut formula

Years to double ≈ 72 ÷ rate. Years to triple ≈ 114 ÷ rate, using the related Rule of 114.

The exact formula

Years to double = ln(2) ÷ ln(1 + rate). This is the same compound interest math solved directly, with no rounding shortcut.

Solving backward

Want to double your money in a specific number of years? Divide 72 by that number to estimate the growth rate you would need.

What is the Rule of 72?

The Rule of 72 is a quick mental-math shortcut that estimates how many years it takes an investment to double, by dividing 72 by the annual growth rate as a percentage.

How accurate is the Rule of 72?

It is very close for typical rates between roughly 5% and 12%. Outside that range the exact formula, ln(2) divided by ln(1 + rate), diverges from the shortcut a bit more.

What is the Rule of 114 or Rule of 144?

The same shortcut works for other multiples: dividing 114 by the rate estimates years to triple your money, and 144 estimates years to quadruple it.

Is this Rule of 72 calculator free and private?

Yes. It is free to use, and every calculation happens locally in your browser rather than being uploaded or stored by the tool.

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