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Rule of 72 Calculator

Years to double an investment at a given rate.

Estimate how long it takes for an investment to double in value at a fixed annual rate of return, using the classic Rule of 72 shortcut and a more accurate ln(2)/r formula for comparison.

Nadia Almasri By Nadia Almasri
Published Last reviewed 1 min read

Inputs

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Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

Rule of 72: years ≈ 72 / rate %. Exact: years = ln(2) / ln(1 + rate / 100).

In depth

Estimate how long it takes for an investment to double in value at a fixed annual rate of return, using the classic Rule of 72 shortcut and a more accurate ln(2)/r formula for comparison.