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Rule of 72 Calculator

Estimate how long it takes to double your money using the Rule of 72, or find the rate needed to double in a given time.

Mode
Rule of 72 Formula
Years to Double = 72 ÷ Interest Rate
72 ÷ 8% = 9.00 years
Estimated doubling time
9.0 years
At a 8% annual rate, your investment will double in approximately 9.0 years.
RateYears to Double
1%72.0 years
3%24.0 years
5%14.4 years
7%10.3 years
10%7.2 years
15%4.8 years
20%3.6 years

How It Works

The Rule of 72 is a simplified formula that estimates the time required to double an investment at a fixed annual rate of return. Divide 72 by the annual interest rate to get the approximate number of years. Conversely, divide 72 by the number of years to find the required rate.

The formula is most accurate for interest rates between 5% and 10%. Outside this range, the rule becomes less precise, though it remains a useful mental shortcut.

This is for informational and educational purposes only.

Rule of 72 Calculator: Guide

Intent
Estimate how long it takes to double your investment using the Rule of 72: Years = 72 ÷ Interest Rate, or find the rate needed to double in a given time.
What it does
Applies the Rule of 72 formula (Years = 72 ÷ Rate) to estimate investment doubling time, or finds the required rate for a target doubling period.
Key features
Years-to-double mode, Rate-to-double mode, Live formula display
Privacy
Everything runs locally in your browser. No data is uploaded.
Best for
  • Quick mental math checks for investment returns
  • Estimating how long until your money doubles at a given rate
  • Understanding the relationship between return rate and time
Why this tool
  • Two calculation modes for flexible use
  • Shows the formula so you learn the rule, not just the result
  • Local-only: no uploads, instant calculation

How to use

  1. 1Choose Years to double or Rate to double mode.
  2. 2Enter the interest rate or target years.
  3. 3Read the estimated result instantly.

Common mistakes

  • The Rule of 72 is an approximation, most accurate for rates between 6% and 10%.
  • The rule assumes annual compounding; more frequent compounding gives slightly faster doubling.
  • This is an educational estimate, not a precise financial projection.

Examples

10% annual return
Rate: 10% Years to double: 7.2 72 ÷ 10 = 7.2 years
Double in 5 years
Target: 5 years Required rate: 14.4% 72 ÷ 5 = 14.4%