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Rule of 69.3 Doubling Time Calculator

Continuous-compounding doubling time vs the rule of 72.

Estimate the doubling time of a continuously compounding investment using the rule of 69.3 (T ≈ 69.3 / r%) and compare it to the popular rule-of-72 estimate. Reports the exact ln(2) / r value too.

Nadia Almasri By Nadia Almasri
Published Last reviewed 1 min read

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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

T_69.3 = 69.3 / r%. T_exact = ln 2 / (r/100). T_72 = 72 / r%.

In depth

Estimate the doubling time of a continuously compounding investment using the rule of 69.3 (T ≈ 69.3 / r%) and compare it to the popular rule-of-72 estimate. Reports the exact ln(2) / r value too.