Compound Lane · Rule of 72
How long until your money doubles?
A mental model: divide 72 by your annual return to estimate the doubling time. Enter a return — the calculator shows the Rule of 72 estimate and the exact value. For contributions and a full schedule, see Compound Interest.
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Two ways to estimate
Rule of 72 (72 ÷ return)—
Exact — ln(2) ÷ ln(1+r)—
Return used—
Here's why
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72 ÷ r is an approximation; the exact doubling time is ln(2)/ln(1+r). The gap is small over common returns. Source & verification date →
Your next step
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Where this fits
Assumptions & methodology
Years to double ≈ 72 ÷ annual return (%). Exact uses ln(2)/ln(1+r) with annual compounding. This is a handy estimate — contributions change the picture.
For exact compounding with contributions, use Compound Interest. Projections are scenarios, not guarantees.
Education, not advice: This tool is for education only and is not personalized financial advice. Returns are not constant in real markets.