Beta
Sensitivity of the stock to a reference market.
Beta is a measure of how sensitive a stock's price is to movements in a reference market — typically the S&P 500 for U.S. equities. A beta of 1 means the stock moves in line with the index: if the S&P rises 2%, the stock rises (on average) 2%. A beta of 2 amplifies moves by 200%; a beta of 0.5 dampens them to 50%.
Beta is calculated as the slope of the regression line between the stock's daily returns and the index's daily returns, typically over a 3–5 year period. It is not fixed: it changes over time as the business or market structure evolves. A company that becomes more defensive over time will see its beta fall; a recently IPO'd startup tends to carry a much higher beta than its long-run equilibrium.
Worked example
Tesla (TSLA) on May 17, 2026, has a historical beta of approximately 2.0. This means that in periods when the S&P 500 falls 10%, Tesla falls on average 20%. In rallies, it rises more. This is not a guarantee — it is a historical average. In individual sessions Tesla can move in the opposite direction from the market.
By contrast, Coca-Cola (KO) carries a beta of roughly 0.6 and Visa (V) approximately 0.9. A portfolio holding 50% Tesla and 50% Coca-Cola would have a weighted beta of 0.5×2.0 + 0.5×0.6 = 1.3 — closer to the market than to Tesla alone, but still more volatile than a pure S&P 500 exposure.
When it's used
Beta is primarily used for portfolio risk management. First, estimating expected volatility relative to the market: a portfolio with a beta of 1.5 amplifies market drawdowns by 50% on average. Second, building a risk-parity portfolio: balancing high-beta names (tech growth) with low-beta ones (utilities, consumer staples) reduces exposure to market cycles. Third, calculating the cost of equity in the CAPM model — though this is primarily academic and analytical use.
Limits
Beta is backward-looking: it measures historical sensitivity, not future sensitivity. A high historical beta on a stock in a sector that has undergone structural change (e.g. a bank after the 2008 crisis) may overstate current risk. Beta also does not capture idiosyncratic risk (company-specific risk: accounting fraud, bankruptcy, loss of a key customer) — only co-movement with the market. A low-beta stock can still fall 70% for internal reasons.
Frequently asked
Can beta be negative?
Yes, rarely. Gold and some safe-haven assets tend to rise when the market falls, producing a negative beta. Among ordinary stocks it is uncommon. In practice, negative-beta instruments in a retail portfolio are almost nonexistent.
Does high beta always mean higher risk?
In the sense of volatility, yes. In the sense of permanent capital loss, no. An excellent company with a beta of 2.0 may fall 30% in a bear market and then fully recover. A company with a beta of 0.5 but deteriorating fundamentals can lose 70% without recovering. Beta measures volatility relative to the market, not the quality of the business.
How often is beta updated?
It is typically calculated on 36–60 months of daily or weekly data. Lucex uses 5-year beta where available, or 2-year beta for recently listed stocks. Structural events — spin-offs, mergers, major business model shifts — can make historical beta unrepresentative of future behavior.
Related terms
Educational definition. Not financial advice.