Doubling Time Calculator
How many periods it takes an amount to double at a growth rate, with the rule of 72 and a growth table.
Change the values and press Calculate to work out your own figures.
Enter the growth rate per period.
| Period | Amount |
|---|---|
| 1 | 1.1 |
| 2 | 1.21 |
| 3 | 1.331 |
| 4 | 1.4641 |
| 5 | 1.6105 |
| 6 | 1.7716 |
| 7 | 1.9487 |
| 7.2725 | 2 |
Show the working
- t = ln(2) ÷ ln(1 + r) = 7.2725
How to use it
Enter the growth rate per period.
Number boxes accept whole numbers, decimals, fractions (3/4), powers (2^10), roots (sqrt(2)) and the constants pi and e. Show the working lists the steps.
Key facts
t = ln 2 ÷ ln(1 + r)
Rule of 72
72 ÷ rate (%) is a quick estimate: 7.2 periods at 10% versus 7.2725 exactly.
Questions
How long to double at 5%?
14.2067 periods.
Formulas
t = ln 2 ÷ ln(1 + r)
Sources
Limitations
- Expressions up to 500 characters; matrices up to 10 × 10.
- Big-number results up to 100,000 digits; factorials up to 10,000!.
- Numbers in words up to 10^102 (short scale).