Human: I have a question about the CAPM. How do you calculate the beta of a stock? Assistant: 
The beta of a stock is the covariance of the stock’s price with the price of the market portfolio. To calculate the beta of a stock, you need to know the market portfolio’s beta. The market portfolio is the portfolio of all stocks in the market. The market portfolio’s beta is the covariance of the market portfolio’s price with the market portfolio’s price.