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Rule of 72

Divide 72 by the annual return rate to estimate the doubling time. Works in either direction.

— or —

Enter one to compute the other. Editing rate computes years; editing years computes rate.

Years to double
—
Implied annual return—
Exact (log) doubling time—
$10,000 in 30 years—
Doublings in 30 years—
Why it works: The exact doubling time is ln(2)/ln(1+r) ≈ 0.693/r for small r. The "72" approximation is accurate within ~1% for rates between 4% and 12%.