Measure a stock's sensitivity to market movements with three linked tools: compute beta directly from historical returns, derive it from correlation and volatility, or estimate the expected return a stock should offer using the Capital Asset Pricing Model (CAPM).
Beta (β) is the most widely used measure of systematic risk — the risk a stock inherits from being part of the overall market. It tells you how many percentage points a stock has historically moved, on average, for every 1% move in the benchmark index, which is almost always the S&P 500. The S&P 500 itself is defined as having a beta of 1.0, so every stock's beta is read relative to that baseline.
A stock with β = 1.0 tends to rise and fall in step with the index. A stock with β = 1.5 has historically amplified market moves by half again: a 10% market rally typically corresponded to a 15% stock gain, and a 10% sell-off to a 15% loss. A stock with β = 0.6, by contrast, dampens swings — roughly a 6% move for every 10% move in the market.
Why does this matter? Because beta drives the expected return investors demand. Under the Capital Asset Pricing Model, the only risk that should be rewarded with higher returns is the risk you cannot eliminate by diversifying — the market-linked component captured by beta. Company-specific risks (a product recall, a CEO departure) can be diversified away and therefore earn no risk premium in theory. When you see analysts argue that a "defensive" utility stock deserves a lower expected return than a high-beta tech stock, beta is the number behind that logic.
Real-world reference points keep beta in perspective: Apple has traded with a beta near 1.2-1.3, Microsoft close to 0.9-1.0, utility stocks around 0.4-0.6, and high-volatility names like Tesla above 2.0. Meanwhile the S&P 500 has delivered roughly a 10% average annual return with 15-18% annualized volatility over the long run (1926-2026) — the numbers this page uses as its market defaults.
There are two mathematically equivalent ways to compute beta, plus a third formula that uses beta once you have it. All three are built into this calculator.
Covariance and variance route (Mode 1). You enter two series of returns from the same periods. The calculator first finds the average return of each series, then computes the sample covariance — the average of the products (stock return − stock mean) × (market return − market mean), divided by n − 1 for a sample. It then divides that by the sample variance of the market series, which is the average squared deviation of market returns from their own mean, also using n − 1. The ratio is the beta. This is the textbook regression approach: beta is simply the slope of the best-fit line when stock returns are plotted against market returns.
Correlation and volatility route (Mode 2). Because covariance equals correlation × σstock × σmarket, the ratio simplifies to β = ρ × (σstock ÷ σmarket). This form is convenient when you already know the stock's correlation with the index and its annualized volatility. Note that correlation is bounded between −1 and 1, so a stock with 30% volatility that is 50% correlated with a 15%-volatility market can have a beta no higher than 1.0 (0.5 × 2). Volatility alone overstates market risk — correlation matters just as much.
CAPM route (Mode 3). Once beta is known, the Capital Asset Pricing Model converts it into a required return. Rf is the risk-free rate (2026 proxies: the 10-year Treasury near 4.0-4.5% or the 3-month T-bill near 4.0%), Rm is the expected market return (about 10% for the S&P 500 long-term), and the difference Rm − Rf is the market risk premium. A stock's own risk premium is β × (Rm − Rf): with β = 1.2, a 4.2% risk-free rate and a 10% market return, the premium is 1.2 × 5.8% = 6.96%, giving an expected return of 4.2% + 6.96% = 11.16%.
A stock has a 0.80 correlation with the S&P 500, annualized volatility of 20%, while the index has 16% volatility.
Volatility ratio = 20% ÷ 16% = 1.25
β = 0.80 × 1.25 = 1.00 — a market-matching stock that offers no amplification of index moves.
Beta is only meaningful relative to 1.0, the market's own value. The table below summarizes the standard interpretation bands used by portfolio managers.
| Beta Range | Label | What It Means | Real-World Examples |
|---|---|---|---|
| β = 1.0 | Market-matching | Moves in line with the benchmark; its expected return equals the market's. | An S&P 500 index fund, Microsoft (~0.9-1.0) |
| β > 1.2 | Aggressive | Amplifies market moves; higher expected return but steeper drawdowns in sell-offs. | Tesla (~2.0+), Apple (~1.2-1.3), many small caps |
| 0.8 ≤ β < 1.2 | Average / in line | Broadly tracks the market with modest deviations in either direction. | Many large-cap blue chips and consumer staples |
| β < 0.8 | Defensive | Dampens market swings; holds up better in downturns but lags in bull markets. | Utilities (~0.4-0.6), healthcare, consumer staples |
| β < 0 | Inverse | Moves opposite the market; acts as a hedge. Rare among individual stocks. | Some gold miners, inverse ETFs, select hedge strategies |
Two cautions when reading any beta. First, beta is a backward-looking statistic: it describes how a stock responded to the market in the sample period, which may not repeat. Second, beta says nothing about a stock's total risk — a low-beta stock can still be highly volatile if much of its risk is company-specific (idiosyncratic). Low beta only means the market has been a small driver of its swings.
Because beta is linear, the beta of a whole portfolio is simply the market-value-weighted average of the betas of its holdings:
For example, a portfolio invested 60% in an aggressive growth fund with β = 1.4 and 40% in a utility ETF with β = 0.5 has a portfolio beta of (0.60 × 1.4) + (0.40 × 0.5) = 0.84 + 0.20 = 1.04 — close to market-neutral despite the aggressive component. If the goal is to reduce sensitivity to market swings, you can lower the portfolio beta by shifting weight toward low-beta assets or cash (β = 0); to pursue higher expected returns, you tilt toward high-beta assets, remembering that expected return rises only for the systematic portion of risk.
A useful 2026 planning context: with the risk-free rate near 4-4.5% and a long-run S&P 500 return near 10%, the market risk premium is roughly 5.5-6%. Every 0.1 of additional portfolio beta therefore adds roughly 0.55-0.6 percentage points of expected annual return under CAPM — and a similar increment of additional drawdown risk in bad years.