Rule of 72 Versus Exact Compound Doubling
Divide 72 by the annual percentage and compare it with the compound-growth logarithm. Both assume an unchanging positive rate, so neither predicts when an actual investment will double.
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How to use this tool
Enter an annual percentage above zero: use 8 for 8%. A loss rate or zero growth does not satisfy this doubling scenario and cannot be meaningfully used in the form.
Results and examples
Read the shortcut beside log(2)/log(1 + rate) and their difference. At low or high rates the shortcut can drift; exact refers only to the fixed annual-compounding identity.
Worked example
At 8%, the rule gives nine years while the logarithmic result is approximately 9.006 years.
Limitations
- Changing returns, tax, fees and inflation are excluded.
- Actual investment returns and capital preservation are not guaranteed.
Fields
| Field | Guidance and constraints |
|---|---|
| Annual return | Accepted range: 0.01–50 · Input step: 0.01 |
Data handling
Processing stays in the current browser tab; the site does not upload tool input for the calculation itself.
Sources
Frequently asked questions
Is the exact value an investment forecast?
No. It is exact only within a constant annual-compounding assumption.
Can I enter a negative return?
This tool covers doubling under positive growth only.
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