basic

Rule of 72 Doubling Time Calculator

t ≈ 72 / r — years to double an investment.

Uses the Rule of 72 to estimate the number of years required to double an investment at a given annual interest rate, and the exact calculation.

Dr. Helena Ortiz By Dr. Helena Ortiz
Published Last reviewed 1 min read

Inputs

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

t_approx = 72 / r; t_exact = ln(2) / ln(1 + r/100)

In depth

Uses the Rule of 72 to estimate the number of years required to double an investment at a given annual interest rate, and the exact calculation.