Basics
Basic4 Min Read
What Is Volatility?
It measures how much the price swings — not which way it is going.
A stock can finish the month up 2%. The same stock can also finish the month up 2% after first falling 18% and then rising 24%. Same result, very different experience. The name of the difference is volatility.
How It's Calculated
Take the standard deviation of daily returns and annualize it. A rough rule: a stock whose daily moves have a standard deviation of 1% has an annual volatility of about 16% (1% × √252, because a year has roughly 252 trading days).
This number is a measurement, not a forecast. "Annual volatility of 40%" says nothing about whether the stock will rise or fall; it only says the price will roam a wide band during the year.
| Typical annual volatility | What it means |
|---|---|
| 10–15% | Utilities, big food brands. The price sits still for days. |
| 15–20% | The S&P 500's long-run band. An index is calmer than its members. |
| 25–40% | Big tech and semiconductors. One earnings night can move it 10%. |
| 60%+ | Recent IPOs, biotech, speculative names. |
An index being calmer than its members is not a coincidence: some of the companies inside rise while others fall, and the moves partly cancel. That is called diversification, and it is the cheapest way to lower volatility.
Realized vs. Implied
There are two different numbers, and they get confused:
- Realized: computed from past prices. It tells you what happened.
- Implied: backed out of option prices. It tells you what the market expects next.
The best known gauge of implied volatility is the VIX: derived from S&P 500 options and nicknamed the "fear index." Its long-run average is around 20. A 12–15 band is a calm market, above 30 is tension, above 50 is panic.
Is Volatility Bad?
No — but it isn't free either. It has two distinct costs:
- Psychological: a high-volatility position can force you to sell along the way, even when you're right.
- Mathematical: volatility eats compound returns. An asset that falls 50% needs to rise 100% to get back to even. Big swings around zero compound to less than small steady steps.
The second point is why, of two assets with the same average return, the calmer one ends up richer over time.
Where You'll See It on This Site
- Day range (stock page): the distance between the day's low and high — the crudest gauge of daily volatility.
- 52-week high / low: the width of the yearly band.
- The intraday chart: flat line or sawtooth — you can tell at a glance.