Doubling Time Calculator
Find out how long it takes an investment or population to double at a given growth rate using this free doubling time calculator.
Enter Values
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Before you rely on this: Estimates only — not financial, tax or legal advice. Confirm current rates, fees and rules before relying on these figures.
How to use this calculator
- Enter the annual growth or interest rate.
- Read the doubling time.
How it works
Exact doubling time = ln(2) ÷ ln(1 + rate). The Rule of 72 (72 ÷ rate%) is a quick mental shortcut.
Worked example
7% a year. Doubles in about 10.24 years (Rule of 72 says ~10.3).
Common mistakes
- Relying only on the Rule of 72 — it drifts at very high or low rates.
- Forgetting inflation, which erodes the real value while the number doubles.
Frequently asked questions
How long does it take for money to double?
Use the Rule of 72: divide 72 by the annual percentage rate. At 6%, money doubles in about 72 ÷ 6 = 12 years.
How accurate is the Rule of 72?
It's a close approximation for rates between about 4% and 12%; the tool also gives the exact figure using logarithms.
Is the Rule of 72 accurate?
It's a close estimate for rates around 6–10%. This tool also shows the exact figure.
Related tools
- Compound Interest Calculator
- Rule of 72 Calculator
- CAGR Calculator
- Future Value Calculator
- FIRE Number Calculator
- Inflation Calculator
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Cite this tool
Zerdly. (2026). Doubling Time Calculator. Retrieved from https://www.zerdly.com/tools/doubling-time-calculator/
Tip: Enter any known values to calculate the remaining results.
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