Doubling Time Calculator
Calculate how long it takes for an investment, population, or any growing quantity to double in size. Uses both the Rule of 70 approximation and exact logarithmic formula.
Calculation Method
Calculate Doubling Time
Enter the annual growth rate (e.g., 7 for 7% per year)
Rule of 70 Result
Formulas
Example
Problem: An investment grows at 7% per year. How long until it doubles?
Rule of 70: 70 ÷ 7 = 10 years
Exact: ln(2) ÷ ln(1.07) = 9.9 years
Real-World Applications
Investment Planning
Calculate how long it takes for investments to double with compound interest.
Population Growth
Estimate when populations will double based on current growth rates.
Business Growth
Project when revenue, customers, or market size will double.
Economic Analysis
Analyze GDP growth, inflation effects, and economic doubling periods.
Rule of 70 Accuracy
| Growth Rate | Rule of 70 | Exact Time | Error |
|---|---|---|---|
| 1% | 70.00 | 69.66 | 0.5% |
| 2% | 35.00 | 35.00 | 0.0% |
| 3% | 23.33 | 23.45 | 0.5% |
| 5% | 14.00 | 14.21 | 1.5% |
| 7% | 10.00 | 10.24 | 2.3% |
| 10% | 7.00 | 7.27 | 3.7% |
| 15% | 4.67 | 4.96 | 5.8% |
| 20% | 3.50 | 3.80 | 7.9% |
Frequently Asked Questions
The Rule of 70 is a quick way to estimate doubling time by dividing 70 by the growth rate percentage. It's quite accurate for growth rates between 1% and 10%, with less than 1% error for most rates in this range.
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