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.
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).
Disclaimer:This tool is provided “as is” for informational and educational purposes only. Results may not be 100% accurate. ToolBird makes no warranties, express or implied, regarding the accuracy, reliability, or completeness of any output generated by this tool. This tool does not constitute professional, legal, financial, medical, or tax advice. Always consult a qualified professional for important decisions. By using this tool, you agree that ToolBird and its operators shall not be held liable for any damages, losses, or consequences arising from the use of this tool or reliance on its results. All processing occurs in your browser — we do not store, transmit, or access your data. Use at your own risk.