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Portfolio beta refers to a popular metric that investors use to measure a portfolio’s potential risk, or its sensitivity to price swings in the broader market. While past performance does not indicate future returns, knowing a portfolio’s beta can help investors understand the historical price variability of their stocks, or how much their holdings may move if there is stock volatility or big gains in a benchmark index, such as the S&P 500.
Investors often consider beta a measure of systematic risk, or risk that stems from the entire market. Macro events such as interest rate or economic changes often fall into the category of systematic risk, while idiosyncratic, stock-specific risk includes events such as a change in company management, new competitors, changed regulation, or product recalls.
Key Points
• Portfolio beta is a metric used to measure the sensitivity of a portfolio’s performance to market movements, indicating its systematic risk.
• To calculate the beta of a portfolio, the beta of each stock is multiplied by its proportional value in the portfolio, and these products are then totaled.
• Stocks with a beta greater than one are considered more volatile than the market, while those with a beta of less than one are viewed as less volatile.
• Negative beta values indicate an inverse relationship to the market, which can be characteristic, under certain circumstances, of assets such as gold or defensive stocks.
• Understanding a portfolio’s beta can be useful for investors aiming to manage risk in alignment with their investment strategy and market outlook.
How to Calculate Beta of a Portfolio
The beta of a portfolio formula requires relatively simple math, as long as investors know the beta for each stock that they hold and the portion of your portfolio that each stock comprises.
Here are the steps to calculate the beta of a hypothetical portfolio:
1. Calculate the total value of each stock in the portfolio by multiplying the number of shares that you own of the stock by the price of its shares:
Stock ABB: 500 shares x $20 a share each = $10,000.
2. Figure out what proportion each stock in the portfolio represents by dividing the stock’s total value by the portfolio’s total value:
Stock ABB’s total value of $10,000/Portfolio’s total value of $80,000 = 0.125.
3. Multiply each stock’s fractional share by its beta. This will calculate the stock’s weighted beta:
Stock ABB’s beta of 1.2 x its fractional portfolio of 0.125 = 0.15.
4. Add up the individual weighted betas.
Here is a hypothetical portfolio with a total beta of 1.22, benchmarked to the S&P 500, which has a beta of 1.0. That means that this portfolio as a whole is considered 22% more volatile than the index.
| Stock | Value | Portfolio Share | Stock Beta | Weighted Beta |
|---|---|---|---|---|
| ABB | $10,000 | 0.125 | 1.20 | 0.15 |
| CDD | $30,000 | 0.375 | 0.85 | 0.319 |
| EFF | $15,000 | 0.1875 | 1.65 | 0.309 |
| GHH | $25,000 | 0.3125 | 1.42 | 0.44375 |
| Sum | 1.22 |
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4 Ways to Characterize Beta
Investors measure a portfolio’s beta against a benchmark index, which is given a value of 1.0. Stocks that have a beta higher than 1.0 are considered more volatile than the overall market, and those with a beta of less than 1.0 are considered less volatile than the overall market.
Understanding beta is part of fundamental stock analysis. Beta is generally used in concert with risk factors to evaluate the potential risk of a portfolio. However, once investors identify the potential risk of a portfolio, they may choose to change their investments or asset allocation in order to increase or decrease its risk.
There are four ways to characterize beta.
High Beta
A high beta stock — one that tends to rise and fall along with the market often — has a value of greater than 1.0. So if a stock has a beta of 1.2 and is benchmarked to the S&P 500, it is seen as 20% more volatile than the broader measure.
If the S&P 500 rises or falls 10%, then the stock may rise or fall 12%, according to its beta. The same would be true for portfolio beta. While there’s more downside risk with high-beta stocks, they might also generate bigger returns when the market rallies, a principle of Modern Portfolio Theory. It’s important to remember, however, that beta is simply an indicator derived from a stock’s past performance and never a guarantee of future performance.
Low Beta
A low beta stock with a beta of 0.5 would be half as volatile as the market. So if the S&P 500 moved 1%, the stock would post a 0.5% swing. Such a stock may have less volatility, but it also may have less potential to post large gains as well.
Still, some investors prefer lower-volatility securities. Low beta investment strategies have shown strong risk-adjusted returns over time, too.
Negative Beta
Stocks or portfolios with a negative beta value inversely correlate with the rest of the market. So when the S&P 500 rises, shares of these companies might instead go down or vice versa.
Gold, for instance, often moves in the opposite direction as stocks, since investors tend to turn to the metal as a haven during stock volatility. Therefore, a portfolio of gold-mining companies could have a negative beta under certain market conditions. However, it’s important to note that this is not always the case. When stocks do well, there could be a zero or even a small positive correlation with gold.
So-called defensive stocks, such as utility companies, also sometimes have negative beta (though they typically have low positive betas), as investors may buy shares when seeking assets that may have lower exposure to market downturns and volatility.
According to the standard Capital Asset Pricing Model (CAPM), a possible downside to negative beta is that the anticipated returns on negative beta securities may be weak — sometimes even less than the risk-free interest rate, though this is not always the case.
Zero Beta
A stock or portfolio can also have a beta of zero, which means it’s uncorrelated with the market. Some hedge funds seek a market-neutral strategy. Being market-neutral means attempting to perform independently of how an index like the S&P 500 behaves.
How to Calculate an Individual Stock’s Beta
For investors, calculating the beta of all their stock holdings can be time consuming, and typically, financial data or brokerage firms offer beta values for stocks.
But if you wanted to calculate beta for an individual stock, you’d divide a measure of the stock’s returns relative to the broader market over a given time frame by a measure of the market’s return relative to its mean, also over the same time frame. Here is the formula:
Beta = Covariance(Rs,Rm) / Variance(Rm)
Covariance is a measure of a security’s returns relative to the market’s returns, where:
Rs = Series of returns of a specific stock over a specific time period
Rm = Series of returns of the broader market over the same time period
Variance is a measure of how widely the market’s returns are dispersed from its historical mean, or average.
Alpha vs Beta vs Smart Beta
Although beta gets its name from the Greek alphabet, it’s not one of the Option Greeks — terminology frequently used by traders to refer to characteristics of specific securities or derivatives in the market. Another commonly used Greek term is alpha. While beta refers to an asset’s volatility relative to the broader market, alpha is a measure of outperformance relative to the rest of the market.
Beta also comes up a lot in the exchange-traded fund, or ETF, industry. Smart beta ETFs are funds that incorporate rules- or factor-based strategies.
What Impacts Beta?
A variety of factors impact an asset’s beta. In general, stocks seen as riskier than average typically feature higher betas. Stock-specific factors, such as debt levels, aggressive management, bold projects, volatile cash flows, and even ESG factors, can influence a stock’s idiosyncratic risk. Higher business risk, while stock-specific, can lead to a more volatile stock price than the overall market, hence a higher beta.
Higher betas often appear in particular stock sectors. There are even investment fund strategies that play on beta. You can buy funds that exclusively own high beta or low beta stocks. A stock’s sector, industry, geographic location, and market cap size can all impact a stock’s volatility and beta.
Cyclical and growth sectors such as energy, industrials, information technology, and consumer discretionary often feature high betas. Utilities, consumer staples, real estate, and much of the health care sector typically have low beta.
Small caps and stocks domiciled in emerging-market economies also often have a higher beta (compared to the U.S. large-cap S&P 500).
Investors may consider the beta of individual investments, among other factors, when determining assets for their self-directed brokerage accounts.
Important Things to Know About Beta
Here are key things to keep in mind when considering the beta of investments:
1. A stock’s beta can change over time. Because beta relies on historical price data, it is subject to change.
2. Beta is not a complete measure of risk. It can be a useful way for investors to estimate short-term risk, but it’s less helpful when it comes to considering a long-term investment because the macroeconomic environment and the company’s fundamentals may change. In some cases, beta is not the best measure of a stock or a portfolio’s risk.
3. Beta is an input when investors are using the Capital Asset Pricing Model (CAPM), a way to measure the anticipated return of assets taking into account systematic risk. It’s a method that also looks at the cost of capital for investors.
4. The estimated beta of a stock is generally less helpful for companies that do not trade as frequently. Thin liquidity for a stock may bias its beta value since there is less robust historical price data.
5. Beta does not offer a complete picture of a stock’s risk profile, as it’s linked to systematic risk. Investors must also consider stock-specific risk when managing the risk of their investments.
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The Takeaway
Beta is a popular metric that investors use to measure a portfolio’s risk, or its sensitivity to price swings in the broader market. Knowing stock holdings’ betas can be important information when you’re building your portfolios.
You can calculate portfolio beta using fairly straightforward math as long as you’re able to obtain the individual betas for your stock holdings. While beta is a helpful tool to try to gauge potential volatility in a portfolio, its reliance on historical data makes it limited in measuring the complete risk profile of an asset or portfolio.
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FAQ
What is a good beta for a portfolio?
What’s considered a good beta will vary depending on an investor’s goals and how much risk they’re ready to accept. For example, a good beta for a portfolio may be considered 1.0 for some investors, since that means the portfolio’s value is roughly as volatile as the market overall. However, some investors may wish to build a portfolio with higher beta, or level of risk, that has the potential to generate higher returns.
What does a beta of 1.3 mean?
A beta of 1.3 means that a portfolio’s value is 30% more volatile than the overall market benchmarked, which is valued at 1.0. This means its value may swing more wildly than the market. So, if the market goes up or down 1%, the portfolio might go up or down 1.3%. However, beta is based on historical performance, and is therefore never a guarantee of how a portfolio will perform in the future.
Why is market portfolio beta 1?
Beta measures a portfolio or asset’s sensitivity relative to the overall market. If a portfolio’s beta is 1.0, it is considered equally as volatile as the market, not more or less so.
How do I reduce my portfolio beta?
One way to reduce your overall portfolio’s beta is to replace higher-beta assets within the portfolio with assets that have lower associated beta, and/or to add more lower-beta assets to the portfolio. However, beta is typically not the only metric investors may consider to gauge risk. Investors may also consider other fundamental factors such as liquidity, creditworthiness, or sensitivity to interest rates when evaluating the risk of portfolio investments.
Is it possible to have a zero-beta portfolio?
It’s technically possible, such as by using market-neutral strategies and holding cash or cash-equivalents. A zero-beta portfolio means the portfolio itself is designed to have no systematic risk. In other words, this portfolio is constructed to have no correlation with the overall movements of the broader stock market. However, a zero-beta portfolio does not mean risk free. Assets may have zero correlation with a benchmark market, but still face risks.
What is the difference between stock beta and portfolio beta?
A stock beta is a measure of an individual stock’s volatility, while portfolio beta is a measure of an overall investment portfolio’s volatility.
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S&P 500 Index: The S&P 500 Index is a market-capitalization-weighted index of 500 leading publicly traded companies in the U.S. It is not an investment product, but a measure of U.S. equity performance. Historical performance of the S&P 500 Index does not guarantee similar results in the future. The historical return of the S&P 500 Index shown does not include the reinvestment of dividends or account for investment fees, expenses, or taxes, which would reduce actual returns.
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