Doubling Time Calculator
Find how long it takes something to double at a steady yearly growth rate. It works for savings, a population, or any amount that grows by the same share each year.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
Doubling time is the natural log of 2 divided by the natural log of one plus the yearly rate, written as a decimal. It assumes the same growth rate every year.
The rule of 72 is a quick check: divide 72 by the rate in percent. It is close for moderate rates and drifts for very high ones.
Worked example
At 7% growth a year, an amount doubles in about 10.2 years. The rule of 72 gives 10.3 years as a quick check.
Questions
Does the rule of 72 always work?
It is an estimate. It is closest for rates between about 6 and 10 percent, and less close for very low or very high rates.
Can this measure a falling amount?
Not directly. It is for amounts that grow. A falling amount takes longer to halve, and this page does not work out that case.
Does inflation count?
If you use a growth rate after inflation, the answer is the time to double in today's money. Otherwise it is the time in future money.
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