⏱️ Rule of 72 Calculator
Instantly calculate how long it takes to double your money at any interest rate — or find the rate you need to double in a specific number of years.
📋 Doubling Time Comparison
| Annual Rate | Rule of 72 (years) | Exact (years) | $10K becomes | Example |
|---|---|---|---|---|
| 2% | 36.0 | 35.00 | $12.2K (10yr) | Savings account |
| 3% | 24.0 | 23.45 | $13.4K (10yr) | Treasury bonds |
| 4% | 18.0 | 17.67 | $14.8K (10yr) | Treasury bonds |
| 5% | 14.4 | 14.21 | $16.3K (10yr) | Corporate bonds |
| 6% | 12.0 | 11.90 | $17.9K (10yr) | Corporate bonds |
| 7% | 10.3 | 10.24 | $19.7K (10yr) | Balanced portfolio |
| 8% | 9.0 | 9.01 | $21.6K (10yr) | Balanced portfolio |
| 9% | 8.0 | 8.04 | $23.7K (10yr) | S&P 500 average |
| 10% | 7.2 | 7.27 | $25.9K (10yr) | S&P 500 average |
| 11% | 6.5 | 6.64 | $28.4K (10yr) | Growth stocks |
| 12% | 6.0 | 6.12 | $31.1K (10yr) | Growth stocks |
| 15% | 4.8 | 4.96 | $40.5K (10yr) | Aggressive growth |
📚 What Is the Rule of 72?
The Rule of 72 is a simple mental math formula used by investors to estimate how long it takes for an investment to double at a given annual rate of return.
The formula: Years to Double = 72 ÷ Annual Return Rate
For example, if you earn 8% per year on your investment, it will take approximately 72 ÷ 8 = 9 years to double your money. At 12% per year, it only takes 6 years.
The rule is most accurate for rates between 2% and 15%. For rates outside this range, the Rule of 69.3 (using natural logarithm) gives a more precise result, but 72 is used because it's easily divisible by many numbers (2, 3, 4, 6, 8, 9, 12).
💡 Why Every Investor Should Know This
Fees Matter More Than You Think
A fund earning 8% with a 2% expense ratio effectively earns 6%. That means doubling in 12 years instead of 9 — 3 extra years per doubling, just from fees.
Inflation Erodes Purchasing Power
At 3% inflation, the purchasing power of your money halves every 24 years. Your investments need to outpace inflation just to break even in real terms.
Start Early, Double More
At 10% annual returns, $10K doubles roughly every 7 years. Over 35 years, that's 5 doublings: $10K → $20K → $40K → $80K → $160K → $320K.
Compare Investments Quickly
Rental property yielding 6%? Doubles in 12 years. Index fund averaging 10%? Doubles in 7.2 years. The Rule of 72 makes these comparisons instant.
Learn Compound Growth
The Rule of 72 is just the beginning. Master the power of compound growth with these essential investing books.
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Note: The Rule of 72 is an approximation. Actual results depend on the compounding frequency, consistency of returns, taxes, and fees. Past returns do not guarantee future performance. This calculator is for educational purposes only.
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