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Rule of 72 Calculator

Estimate doubling time and compare it with the exact compound-growth result.

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Inputs

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Result

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Calculated locally
Rule of 72 doubling time
—
Exact doubling time
—
Approximation difference
—

Saved locally, explained clearly

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Calculation steps

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  1. 1

    Formula selected

    The calculator uses the following formula or method.

    Estimated doubling years = 72 ÷ annual rate

    The exact result is ln(2) ÷ ln(1 + rate).

  2. 2

    Values entered

    Your values are placed into the calculation.

    Enter values to see what is used in this step.

  3. 3

    Result calculated

    The formula or method produces the following result values.

    Results will appear after a successful calculation.

  4. 4

    Answer formatted

    Displayed values are rounded and formatted using each output’s configured precision.

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How it works

Divide 72 by the annual percentage rate for a quick doubling estimate. The calculator also shows the exact compound-growth time.

Input query strings and outputs

Use an input name in this page’s URL as ?name=value, and join additional inputs with &. Portable shared links may instead use the compact ?ac= state parameter.

Input query strings

1
  • ?annualRate= Annual growth rate

    Percentage · Required · Default: 8

Outputs

3
  • ruleOf72Years Rule of 72 doubling time

    Number · Primary output · Suffix: years

  • exactYears Exact doubling time

    Number · Suffix: years

  • difference Approximation difference

    Number · Suffix: years

Limits

The rule is an approximation and assumes a constant positive return.

Sources
  • No external reference is listed for this calculator. Its formula and variable definitions are shown above.
Limitations
  • The exact result is ln(2) ÷ ln(1 + rate).
  • Estimates use the rates, timing, and assumptions entered. Fees, taxes, lender rules, and future changes are included only where explicitly shown.

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