Investing shortcut

Rule of 72 Calculator

Estimate doubling time in seconds, then compare the shortcut with the exact compound-growth formula.

Input

%
Assumes a constant annual return with annual compounding and no deposits or withdrawals.

Results

Rule of 72 estimate—
Exact doubling time—
Approximation difference—
Growth after 10 years—

Why divide 72 by the rate?

The Rule of 72 is a mental-math shortcut. Divide 72 by a percentage return to approximate the number of years required to double. It is most useful for ordinary positive rates and becomes less precise at unusually high rates.

Rule of 72: years ≈ 72 ÷ rate
Exact: years = ln(2) ÷ ln(1 + rate)

Use it as a quick check

The result is a comparison tool, not a promise. Investment returns vary from year to year, and fees, taxes and inflation affect real purchasing power.