Guide · Markets
Beta: How Much a Stock Actually Moves With the Market
A beta of 1.5 doesn't mean a stock is '50% riskier' in the way most people assume — it measures something more specific than that.
Beta measures how much a stock's price has historically moved relative to a broad market index — usually the S&P 500, which is assigned a beta of exactly 1.0 by definition. A stock with a beta of 1.5 has historically moved about 50% more than the index in the same direction; a beta of 0.5 means it moved about half as much.
The "same direction" part matters. Beta doesn't measure whether a stock tends to rise or fall overall — that's a separate question about expected return — it measures amplitude relative to the market's own swings. A high-beta stock isn't necessarily a bad investment; it's one that amplifies whatever the broader market is already doing, for better or worse.
A negative beta, while rare, means a stock has historically moved opposite the market — gold-mining stocks and some defensive sectors occasionally show mild negative beta during specific stretches, which is part of why they get discussed as portfolio diversifiers.
Beta is calculated from historical price data, which means it's a backward-looking description, not a guarantee — a stock's beta during a calm multi-year stretch can look very different from its behavior during a sudden market shock, when correlations across nearly everything tend to rise together regardless of each stock's historical beta.