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Rule of Calculator
Quick answer
If annual return is 8%, the approx. doubling time is 9 years.
Rule of 72: Years to double ≈ 72 ÷ annual return (%).
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0.1 %50 %
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Approx. doubling time
9years
The number of whole years, rounded down to the last completed year.
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About the Rule of Calculator
The Rule of 72 is a quick way to estimate how many years it takes for money to double: divide 72 by the annual rate of return. At 8% a year, money doubles in about 72 ÷ 8 = 9 years.
It is an approximation, most accurate for rates between about 6% and 10%.
Rule of 72
Years to double ≈ 72 ÷ annual return (%)
Things to keep in mind
- It works the same way for inflation: at 6% inflation, prices double in about 12 years.
- For an exact answer, use the Compound Interest or Future Value calculator.
- The rule assumes returns compound every year.
See how the result changes
Each table re-runs this calculator with one value changed and everything else left as it is.
Approx. doubling time by annual return
If annual return goes from 8% to 12%, approx. doubling time changes from 9 years to 6 years (−33%).
| Annual return | Approx. doubling time |
|---|---|
| 4% | 18 years |
| 6% | 12 years |
| 8%start | 9 years |
| 12% | 6 years |
| 16% | 4.5 years |
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1
Enter Annual return
Provide your annual return, in %.
2
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This finance tool works out your approx. doubling time instantly, so you don't have to do the math by hand.
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What Affects Your Approx. doubling time
Your approx. doubling time depends on the values below.
Annual return
Changing your annual return changes your approx. doubling time. Typically between 0.1 and 50 %.
Example Result
Here's what you can expect from a rule of calculation:
- Annual return
- 8 %
- Approx. doubling time
- 9 years
Frequently Asked Questions
- How does annual return affect approx. doubling time?
- If annual return goes from 8% to 12%, approx. doubling time changes from 9 years to 6 years (−33%).
- How to calculate rule of?
- Fill in annual return in the Rule of Calculator above and your approx. doubling time is calculated instantly. Change any value to see how the result responds.
- What does an example rule of calculation look like?
- If annual return is 8%, the approx. doubling time is 9 years.
- Is this calculator free to use?
- Yes — every calculator on this site is completely free, with no sign-up or account required.
- How accurate is this calculator?
- It uses the standard formula and calculates on our server for every request, so results are precise for the values you enter.
- Is my data saved anywhere?
- No. Nothing you enter is stored or sent anywhere unless you choose to share a link with your values included.
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