Rule of 72 Calculator
Calculate how long it takes your investment to double using the Rule of 72, Rule of 70, and Rule of 69.3. Compare accuracy across methods.
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Reference: Doubling Times for Common Rates
| Rate | Rule of 72 | Rule of 70 | Rule of 69.3 | Exact | Error (72) |
|---|---|---|---|---|---|
| 1% | 72.00 | 70.00 | 69.30 | 69.66 | 3.4% |
| 2% | 36.00 | 35.00 | 34.65 | 35.00 | 2.8% |
| 3% | 24.00 | 23.33 | 23.10 | 23.45 | 2.3% |
| 4% | 18.00 | 17.50 | 17.32 | 17.67 | 1.9% |
| 5% | 14.40 | 14.00 | 13.86 | 14.21 | 1.4% |
| 6% | 12.00 | 11.67 | 11.55 | 11.90 | 0.9% |
| 7% | 10.29 | 10.00 | 9.90 | 10.24 | 0.4% |
| 8% | 9.00 | 8.75 | 8.66 | 9.01 | -0.1% |
| 9% | 8.00 | 7.78 | 7.70 | 8.04 | -0.5% |
| 10% | 7.20 | 7.00 | 6.93 | 7.27 | -1.0% |
| 12% | 6.00 | 5.83 | 5.77 | 6.12 | -1.9% |
| 15% | 4.80 | 4.67 | 4.62 | 4.96 | -3.2% |
| 18% | 4.00 | 3.89 | 3.85 | 4.19 | -4.5% |
| 20% | 3.60 | 3.50 | 3.46 | 3.80 | -5.3% |
| 25% | 2.88 | 2.80 | 2.77 | 3.11 | -7.3% |
How to Use the Rule of 72 Calculator
- Enter your annual interest rate (or select a common rate).
- Optionally enter an initial amount to see the doubling chain.
- View doubling time estimates using all three rules plus the exact formula.
- Compare accuracy in the reference table below.
About the Rules
- Rule of 72: Divide 72 by your rate. Most accurate at 6-10%.
- Rule of 70: Divide 70 by your rate. Better for lower rates.
- Rule of 69.3: Divide 69.3 by your rate. Most accurate for continuous compounding.
- All are approximations of the exact formula: ln(2) / ln(1 + r).
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Disclaimer: This tool is provided as-is for informational and educational purposes only.