Doubling Time Calculator
A free, browser-based calculator. Runs entirely in your browser — no sign up, nothing stored.
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Enter Values
Enter your values and press Calculate to see results.
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
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
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.