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Rule of 72 Calculator

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Estimate how long money takes to double at a given return — or the rate needed.

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Rule of 72 is an approximation (years ≈ 72 ÷ rate%). Not investment advice.

Estimate

Years to double
9 yrs

Exact compound estimate: ~9.01 years (ln 2 / ln(1+r)).

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How to Use

  1. 1 Choose Rate → years or Years → rate
  2. 2 Enter the percentage or years
  3. 3 Read the Rule of 72 estimate
  4. 4 Compare with the exact compound estimate when shown

Features

  • Years from rate or rate from years
  • Exact compound comparison for rate mode
  • Educational disclaimer
  • Client-side

Why it Matters

The Rule of 72 is the fastest mental model for when does this double — useful for teaching compound growth without a full amortization sheet.

★★★★★

Years to double ≈ 72 ÷ annual return %. Educational approximation — not investment advice.

Frequently Asked Questions

Is the rule exact?
No — approximation. We also show exact years via natural log when converting from rate.
Investment advice?
No — educational estimate only.
Works for debt?
Same math for roughly estimating doubling of debt at a fixed rate.
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