Daily volatility (σ) is the typical day-to-day price swing for a stock, in dollars, measured over a trailing window.
Not by itself. Volatility measures how far a price swings, not which way it goes. A volatile stock gives larger gains and larger losses than a steady one, so it asks for a stronger stomach and a smaller share of a portfolio, but it is not automatically a bad company.
Take the day-to-day percentage changes in a stock over a trailing window, such as 30 trading days, and measure how widely they spread around their average. The result is the standard deviation, usually written σ. A higher σ means bigger typical daily moves.
It is relative. A daily swing that is ordinary for a small technology company would be unusual for a utility, so compare a stock with its own history and with its sector.
No. Calm periods can end suddenly. Volatility describes recent behavior and says nothing certain about what comes next.
AAPL analysis shows this metric in context, or browse all S&P 500 tickers.
Educational research only — not investment advice.