Free Rule of 72 Calculator: Investment Doubling Time Predictor
Apply the Rule of 72 to instantly find out how long it takes to double your money at any interest rate. Includes benchmark comparisons across savings, index funds, and growth equity.
Setup Rate
Comparison Benchmarks
See how different interest rates impact the time it takes to double your capital.
| Investment Profile | Annual Rate | Calculation | Years to Double |
|---|---|---|---|
| ConservativeSavings Account | 3% | 72 ÷ 3 | 24 Years |
| ModerateHigh Yield Savings | 5% | 72 ÷ 5 | 14.4 Years |
| GrowthIndex Fund | 7% | 72 ÷ 7 | 10.3 Years |
| RapidAggressive Growth | 10% | 72 ÷ 10 | 7.2 Years |
| BoldHigh Growth Equity | 12% | 72 ÷ 12 | 6 Years |
| SpeculativeVenture Investment | 15% | 72 ÷ 15 | 4.8 Years |
How It Works
The Rule of 72 is a simplified financial shortcut used to estimate the doubling time of an investment. By dividing the number 72 by your annual interest rate, you can instantly determine how many years are required for your capital to increase by 100%. While mathematically an approximation, it is highly accurate for standard market returns and serves as a powerful mental model for evaluating Compound Interest potential.
What You'll Get
Doubling Time Analysis
Identify the exact year count required to hit your 2x goal. Our utility compares your specific rate against traditional benchmarks (Index Funds vs. HYSA) to provide meaningful context.
Growth Velocity Rating
Understand whether your rate is considered "Stable," "Compounding," or "Aggressive." See how many doubling cycles your investment will complete within a single decade.
Accuracy & Limitations
The Rule of 72 is most precise for interest rates between 5% and 12%. For accounts with continuous compounding or extremely high-volatility returns, the precision may vary slightly. Additionally, this calculation does not account for recurring contributions. To see how monthly deposits can accelerate your doubling time, we recommend using our Savings Growth Engine.