Rule of 72 Calculator

Use the Rule of 72 to estimate how many years it takes to double money at a given annual return, or the rate required to double in a target time.

941.4K uses Updated · 2026-05-14 Runs locally · zero upload
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The Rule of 72 is a quick mental model for estimating how long it takes a compounding investment to double. Dividing 72 by the annual rate of return yields the number of years required. The calculator supports both directions — from rate to years and from years to rate — and shows the exact value computed from the compounding formula for comparison.

How to Use Rule of 72 Calculator

  1. Choose a mode: convert from a rate to doubling years, or from target years to required rate.
  2. Enter the annual return rate (or target years).
  3. Read both the Rule-of-72 estimate and the exact compounding value.

Formula & Theory - Rule of 72 Calculator

years_to_double ≈ 72 / rate_percent
rate_percent ≈ 72 / years_to_double
exact_years = ln(2) / ln(1 + rate)            // precise compounding
exact_rate  = 2^(1/years) - 1                 // precise compounding

Use Cases for Rule of 72 Calculator

  • Quickly estimate doubling time for retirement investments.
  • Compare savings vehicles using a mental math shortcut.
  • Teach compounding intuition to students or clients.
  • Approximate inflation’s impact on purchasing power over time.

Frequently asked questions about Rule of 72 Calculator

How accurate is the Rule of 72?

It is most accurate between 4% and 15% annual returns. Outside that range you may prefer the exact compounding formula.

Does it work for monthly compounding?

The rule assumes annual compounding. For monthly or continuous compounding, prefer the precise logarithmic formula provided in the result panel.

Can it estimate halving time (e.g., inflation)?

Yes. Divide 72 by the annual inflation rate to estimate how many years until purchasing power halves.

Is my data stored?

No. Calculations run only in your browser.