Rule of 72 Calculator
Estimate how long it takes an investment to double using the rule of 72 with this free finance calculator in your browser.
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter your annual return.
- Press Calculate.
How it works
Years to double ≈ 72 ÷ annual return — a quick mental estimate of compound growth.
Worked example
8% return. ≈ 9 years to double.
Common mistakes
- Relying on it at very high or low rates, where it drifts from the exact figure.
- Forgetting inflation, which erodes the real value while the number doubles.
Frequently asked questions
How accurate is the Rule of 72?
It's a close estimate for rates around 6–10%; outside that range the exact formula is better.
Can I use it for inflation?
Yes — 72 ÷ inflation rate estimates how long until prices double (and money halves in value).
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Cite this tool
Zerdly. (2026). Rule of 72 Calculator. Retrieved from https://www.zerdly.com/tools/rule-of-72-calculator/
Tip: Enter any known values to calculate the remaining results.
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