Investment Doubling Time Calculator
Years to double your money.
Calculate years needed to double an investment at a given return rate. Runs in your browser with a transparent formula — free and no signup.
What this tool does
Enter annual rate. The tool shows doubling time using exact formula and Rule of 72 approximation.
Enter Values
Formula Used
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Calculations, display, or translation — let us know.
Disclaimer
Results are estimates for educational purposes only. They do not constitute financial advice. Consult a qualified professional before making financial decisions.
7% return: doubles in 10.24 years exact, 10.29 via Rule of 72. Higher rates shorten doubling dramatically: 10% = 7.3 years; 5% = 14.2 years. Rule of 72 close enough for mental math at 4-12% rates.
Quick example
With annual rate of 7%, the result is 10.2 years. Change any figure and watch the output shift — it's often more useful to see the pattern than to memorise the formula.
What's happening under the hood
Exact natural log formula. Rule of 72 = 72/rate. The formula is listed in full below. If the number looks off, you can retrace the calculation by hand — that's the point of showing the working.
How to use this beyond the first run
Re-run the calculation once a year. Life changes — pay rises, new expenses, interest-rate shifts — and the figure that looked right 12 months ago often isn't today. Annual recalibration keeps the plan honest.
What this doesn't capture
The calculation assumes a steady savings rate and a stable interest rate. Real saving journeys include emergencies, windfalls, and rate changes — especially in easy-access products. The figure is a direction of travel, not a guarantee.
Where to go next
This calculation rarely sits alone in a planning exercise. If you're running these numbers, you'll probably also want the rule of 72 calculator, the compound interest calculator, and the lump sum investment calculator — each one answers a different question in the same territory. Treating them as a set rather than in isolation usually produces a more honest picture.
Doubling time produces years based on the inputs provided.
Inputs
This example uses typical values for illustration. Adjust the inputs above to match a specific situation and see how the result changes.
Sources & Methodology
Methodology
Exact natural log formula. Rule of 72 = 72/rate.
References
Frequently Asked Questions
Rule of 72 vs exact?
Rule of 70 vs 72?
Works on declining value?
Negative rates?
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