Beta: Definition, Calculation, and Explanation for Investors
Beta (β) measures the volatility—or systematic risk—of a security or portfolio compared to the market as a whole (usually the S&P 500). Stocks with betas higher than 1.0 can be interpreted as more volatile than the S&P 500.
Beta is used in the capital asset pricing model (CAPM), which describes the relationship between systematic risk and the expected return on assets (usually stocks). CAPM is widely used for pricing risky securities and generating estimates of the expected returns of assets, considering both the risk of those assets and the cost of capital.
How Beta Works
A beta coefficient can measure an individual stock’s volatility compared to the entire market’s systematic risk. In statistical terms, Beta represents the slope of the line through a regression of data points. In finance, each data point represents an individual stock’s returns against the market’s.
Beta effectively describes the activity of a security’s returns as it responds to swings in the market. A security’s Beta is calculated by dividing the product of the covariance of the security’s returns and the market’s returns by the variance of the market’s returns over a specified period.
The calculation for Beta is as follows:
Beta coefficient() = covariance Variance:=the return on an individual stock=the return on the overall marketCovariance is how changes in a stock’s returns are related to changes in the market’s returnsVariance is how far the market’s data points spread out from their average value
The beta calculation is used to help investors understand whether a stock moves in the same direction as the rest of the market. It also provides insights into how volatile the stock is relative to the rest of the market. For Beta to provide helpful insight, the market set as a benchmark should be related to the stock. For example, they are calculating a bond ETF’s Beta using the S&P 500 as the benchmark would not provide much helpful insight for an investor because bonds and stocks are too dissimilar.
Understanding Beta
An investor uses Beta to gauge how much risk a stock adds to a portfolio. While a stock that deviates very little from the market doesn’t add a lot of risk to a portfolio, it also doesn’t increase the potential for greater returns.
Make sure that a specific stock is being compared to the proper benchmark; it should have a high R-squared value about the benchmark. R-squared is a statistical measure that shows the percentage of a security’s historical price movements that movements in the benchmark index can explain. When using Beta to determine the degree of systematic risk, a security with a high R-squared value about its benchmark could indicate a more relevant benchmark.
For example, a gold exchange-traded fund (ETF), such as the SPDR Gold Shares (GLD), is tied to the performance of gold bullion.1 Consequently, a gold ETF would have a low beta and R-squared relationship with the S&P 500.
One way for a stock investor to think about risk is to split it into two categories. The first category is systematic risk, the risk of the entire market declining. The financial crisis is a systematic risk event; no diversification could have prevented investors from losing value in their stock portfolios. Systematic risk is also known as un-diversifiable risk.
Unsystematic risk, a non-diversifiable risk, is the uncertainty associated with an individual stock or industry. For example, the surprise announcement that Lumber Liquidators (LL) had been selling hardwood flooring with dangerous levels of formaldehyde in 2015 is an example of unsystematic risk.2 It was a request that was specific to that company. Unsystematic risk can be partially mitigated through diversification.
A stock’s Beta will change over time as it relates its performance to the overall market’s returns, which is a dynamic process.
Types of Beta Values
Beta Value Equal to 1.0
If a stock has a beta of 1.0, it indicates that its price activity is strongly correlated with the market. A stock with a beta of 1.0 has systematic risk. However, the beta calculation can’t detect any unsystematic risk. Adding a stock to a portfolio with a beta of 1.0 doesn’t add any risk to the portfolio. Still, it also doesn’t increase the likelihood of the portfolio providing an excess return.
Beta Value Less Than One
A beta value less than 1.0 means that the security is theoretically less volatile than the market. Including this stock in a portfolio makes it less risky than the same portfolio without the stock. For example, utility stocks often have low betas because they move more slowly than market averages.
Beta Value Greater Than One
A beta greater than 1.0 indicates that the security’s price is theoretically more volatile than the market. For example, if a stock’s Beta is 1.2, it is assumed to be 20% more volatile than the market. Technology and small-cap stocks tend to have higher betas than the market benchmark. This indicates that adding the stock to a portfolio will increase its risk but may also increase its expected return.
Negative Beta Value
Some stocks have negative betas. A beta of -1.0 means that the stock is inversely correlated to the market benchmark on a 1:1 basis. This stock could be considered the opposite, an error image of the benchmark’s trends. Put options and inverse ETFs are designed to have negative betas. There are also a few industry groups, like gold miners, where a negative beta is standard.
Beta in Theory vs. Beta in Practice
The beta coefficient theory assumes that stock returns are normally distributed from a statistical perspective. However, financial markets are prone to significant surprises. In reality, returns aren’t always normally distributed. Therefore, what a stock’s Beta might predict about a stock’s future movement isn’t always true.
A stock with a very low beta could have smaller price swings, yet it could still be in a long-term downtrend. So, adding a down-trending stock with a low beta decreases the risk in a portfolio only if the investor defines risk strictly in terms of volatility (rather than as the potential for losses). From a practical perspective, a low-beta stock experiencing a downtrend isn’t likely to improve a portfolio’s performance.
Similarly, a high-beta stock that is volatile in a primarily upward direction will increase the risk of a portfolio, but it may also add gains. It’s recommended that investors use Beta to evaluate a stock from other perspectives—such as fundamental or technical factors—before assuming it will add or remove risk from a portfolio.
Drawbacks of Beta
While Beta can offer helpful information when evaluating a stock, it has some limitations. Beta helps determine a security’s short-term risk and analyzes volatility to determine equity costs when using the CAPM. However, since Beta is calculated using historical data points, it becomes less meaningful for investors looking to predict a stock’s future movements. Beta is also less helpful for long-term investments since a stock’s volatility can change significantly annually, depending on the company’s growth stage and other factors. Furthermore, the beta measure on a particular stock tends to jump around over time, which makes it unreliable as a stable measure.
What Is a Good Beta for a Stock?
Beta is your proxy for a stock’s riskiness or volatility relative to the broader market. A good beta will, therefore, rely on your risk tolerance and goals. If you wish to replicate the broader market in your portfolio via an index ETF, a beta of 1.0 would be ideal. A lower beta may be more appropriate if you are a conservative investor looking to preserve principal; in a bull market, betas more significant than 1.0 will tend to produce above-average returns, but they will also produce more significant losses in a down market.
Is Beta a Good Measure of Risk?
Many experts agree that while Beta provides some risk information, it is not an adequate measure. Beta only looks at a stock’s past performance relative to the S&P 500 and provides forward guidance. It also does not consider the fundamentals of a company or its earnings and growth potential.
How Do You Interpret a Stock’s Beta?
A Beta of 1.0 for a stock means it has been just as volatile as the broader market (i.e., the S&P 500 index). If the index moves up or down 1%, so too would the stock, on average. Betas larger than 1.0 indicate greater volatility, so if the Beta were 1.5 and the index moved up or down 1%, the stock would have moved 1.5% on average. Betas less than 1.0 indicate less volatility: if the stock had a beta of 0.5, it would have risen or fallen just half a percentage. The index moved 1%.
Conclusion
- Beta (β), primarily used in the capital asset pricing model (CAPM), is a measure of the volatility–or systematic risk–of a security or portfolio compared to the market as a whole.
- Beta data about an individual stock can only give an investor an approximation of how much risk the stock will add to a (presumably) diversified portfolio.
- For Beta to be meaningful, the stock should be related to the benchmark used in the calculation.
- The S&P 500 has a beta of 1.0.
- Stocks with betas above one will tend to move more than the S&P 500; stocks with less than one will move with less momentum.
