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Beta is a measure of a stock’s volatility in relation to the overall market. It is a key component in the Capital Asset Pricing Model (CAPM), which investors use to calculate expected return on investment, taking into account the risk-free rate of return, the investment’s beta, and the expected market return.


Beta indicates how much a stock’s price is expected to fluctuate compared to the market as a whole. A beta value:

  • Greater than 1 implies the stock is more volatile than the market.
  • Equal to 1 suggests the stock’s volatility is in line with the market.
  • Less than 1 indicates the stock is less volatile than the market.


Beta is calculated using regression analysis. It compares the returns of the stock to the returns of a market index (such as the S&P 500) over the same period. The formula for beta is:

Beta = Covariance(Stock Returns, Market Returns) / Variance(Market Returns)


  • Covariance measures how the stock’s returns move with the market’s returns.
  • Variance is a measure of how the market’s returns spread out from their average.


Suppose you want to calculate the beta of Company XYZ relative to the S&P 500 index. You collect weekly return data for both the company and the S&P 500 over the past year and find:

  • The covariance between XYZ’s returns and the S&P 500’s returns is 0.002.
  • The variance of the S&P 500’s returns over the same period is 0.0015.

Using the beta formula: Beta = 0.002 / 0.0015 = 2 / 1.5 = 1.33

This beta value of 1.33 suggests that Company XYZ’s stock is 33% more volatile than the market. If the market goes up or down, XYZ’s stock is expected to go up or down by 33% more, on average.

Usage in Financial Analysis

  • Risk Management: Investors use beta to understand and manage the risk of their portfolio relative to the market.
  • Portfolio Construction: Beta helps in building a diversified portfolio that matches an investor’s risk tolerance. For instance, a risk-averse investor might prefer stocks with a beta less than 1.
  • Performance Evaluation: Beta allows investors to gauge if a stock’s returns are due to market movements or the company’s individual performance.

It’s important to note that beta is just one measure of risk and should be used alongside other metrics and qualitative factors when making investment decisions.