Enter the growth rate per period to see how many periods it takes for a value to double.
Doubling Time Calculator
Growth rate:% per period
Doubling time:
—
periods
Details:
Doubling-time formula
For exponential growth (compound interest), the exact formula is T = ln(2) ÷ ln(1 + r/100), where r is the percentage growth rate per period. The Rule of 70 gives the quick estimate T ≈ 70 ÷ r.
Practical examples
| Rate per period | Exact time | Rule of 70 |
|---|---|---|
| 1% | 69.66 periods | 70 periods |
| 2% | 35.00 periods | 35 periods |
| 5% | 14.21 periods | 14 periods |
| 7% | 10.24 periods | 10 periods |
| 10% | 7.27 periods | 7 periods |
| 12% | 6.12 periods | 5.83 periods |
Frequently asked questions
How do you calculate doubling time?
Use T = ln(2) / ln(1 + r/100) for the exact result, or T ≈ 70 / r for a quick estimate.
What is the Rule of 70?
Divide 70 by the percentage growth rate to estimate the doubling time.
Does the formula work for investments and populations?
Yes, it applies to exponential growth, including compound interest and population growth.
Can I use a comma as the decimal separator?
Yes. Both commas and decimal points are accepted.
See also…
