Stock Beta Calculator

What Beta Tells You

Beta is the single most widely used measure of a stock's systematic risk — the portion of its volatility that comes from the market as a whole rather than from the company itself. A beta of 1.0 means the stock has historically moved roughly in lockstep with the S&P 500. A beta of 1.5 means that when the market rises or falls 1%, this stock has tended to move about 1.5% in the same direction. A beta of 0.5 means it moves half as much — it dampens market swings instead of amplifying them.

Mathematically, beta is the slope of a regression line fit through a stock's returns plotted against the market's returns: Beta = Covariance(stock, market) / Variance(market). This calculator uses weekly returns for the stock and for SPY (an S&P 500 ETF proxy) over your chosen lookback, then fits that line. The scatter chart shows every week as a dot; the orange line is the regression fit, and its steepness is beta.

Read beta alongside R² (R-squared). R² tells you how much of the stock's movement the market actually explains. A blue-chip industrial might show a beta near 1.0 with a high R² — beta describes it well. A biotech or a meme stock can show a similar beta but a low R², meaning most of its movement is idiosyncratic and its beta is far less meaningful. Always check both numbers before trusting a beta.

How Investors Use Beta

Portfolio managers use beta to control risk. Blending low-beta defensives (utilities, staples) with high-beta growth names lets you dial a portfolio's overall market sensitivity up or down. Beta is also a direct input to the Capital Asset Pricing Model (CAPM), which estimates a stock's cost of equity as the risk-free rate plus beta times the equity risk premium. That cost of equity feeds straight into a WACC calculation and therefore into any DCF valuation — a higher beta means a higher discount rate and a lower intrinsic value, all else equal.

Beta has real limits worth remembering. It is backward-looking — it describes how a stock behaved, not how it will behave — and it can shift as a company's business, leverage, or size changes. It says nothing about whether a stock is cheap or expensive, only how it moves. And a low R² can make a headline beta misleading. Use beta as one lens on risk, not a verdict.