Definition
Volatility is typically calculated from historical returns ('realized volatility') or implied from option prices ('implied volatility', or IV). The VIX index measures 30-day implied volatility on the S&P 500 and is often called the 'fear gauge' — spikes above 30 usually accompany market stress. Volatility is not the same as risk, though it's a common proxy. High volatility means larger price swings, which can be either opportunity or hazard depending on your position and time horizon. Long-term investors often ignore short-term volatility, while day traders depend on it for trading opportunities.
Realized volatility (annualized) = σ × √252
σ = standard deviation of daily log returns; 252 = approximate trading days per year
Example
If a stock has a daily standard deviation of 1.5%, its annualized volatility is 1.5% × √252 ≈ 23.8%. Compare: SPY typically shows 12–18% annualized vol; individual tech names 30–50%; small biotech can exceed 80%.
Frequently Asked Questions
Is volatility the same as risk?
Volatility is often used as a proxy for risk but they aren't identical. Real risk is 'permanent loss of capital'; volatility just measures price fluctuation. A stock can be volatile without being risky, and vice versa.
What is the VIX?
The CBOE Volatility Index — a real-time measure of 30-day implied volatility on S&P 500 options. Values below 15 imply calm; 20–30 elevated; 30+ significant stress.
How can I reduce portfolio volatility?
Diversify across uncorrelated assets, add bonds or cash equivalents, or use lower-beta stocks. Options strategies (covered calls, protective puts) can also dampen volatility.