Rule of 72 Calculator
By Miikka · CalcBrew · Updated
10.3 yrs
Doubling time (Rule of 72)
| Rule of 72 | 10.3 yrs |
| Exact doubling time | 10.2 yrs |
| Quadrupling time | 20.5 yrs |
How long does it take for an investment to double at a given annual return? This Rule of 72 calculator answers with the quick Rule of 72 and the exact mathematical formula, and it also shows when your capital quadruples.
How the calculator works and what it’s for▾
What the Rule of 72 is
The Rule of 72 is a quick rule of thumb: divide 72 by your annual return to estimate the years it takes to double. At an 8% return, for instance, 72 divided by eight is about 9 years.
The exact doubling time uses the formula ln(2)/ln(1+return), which gives the mathematically correct result. The Rule of 72 stays close to it at typical return rates.
What you enter and what you get
You enter just one number: your assumed annual return as a percentage.
You get the doubling time by the Rule of 72, the exact doubling time from the formula, and the time to quadruple, which is simply doubling twice in a row.
Where it helps
The calculator illustrates the power of compounding and helps you grasp how the return rate affects how fast an investment grows.
It suits investment planning, comparing different return assumptions, and setting long-term goals.
Interpretation and tips
Even a small difference in annual return shortens the doubling time surprisingly much, because growth is exponential rather than linear.
Use a realistic return assumption and remember that inflation, taxes, and fees lengthen the real doubling time in practice.
🔄 Reviewed June 2026
Frequently asked questions
Cite this calculator
CalcBrew. (2026). Rule of 72 Calculator. https://calcbrew.com/rule-of-72-calculator“Rule of 72 Calculator.” CalcBrew, 2026, calcbrew.com/rule-of-72-calculator.Link to https://calcbrew.com/rule-of-72-calculator. Results are estimates; cite the underlying formula or data source for academic work.
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