# Beta 60 Month

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## Definition

YCharts calculates the 60 month market beta by regressing stock returns less the risk free rate of returns on the market returns less the risk free rate of return (Market returns come from the S&P 500 Total Returns Index (SPXTR), and the risk free rate is the 4 Week Average T-Bill (Monthly). There must be a minimum of 36 months of stock returns for a company to have its beta calculated.

Beta is a measure of the risk of a stock when it is included in a well-diversified portfolio.

In financial theory, the Capital Asset Pricing Model breaks down expected stock returns into two components. The first is the return that would be expected based on covariance with the movements of the market (for most stocks, when the market as a whole goes up, the price of the stock will also go up). The second part is the increase in the price of a stock that is not explained by the market. The first part - covariance with the market - is what Beta captures.

When Beta is positive, the stock price tends to move in the same direction as the market, and the magnitude of Beta tells by how much. If a stock's Beta is greater than 1, that means that when the market index goes up 1%, we expect the stock will go up by more than 1%. On the contrary, if the market goes down by 1%, we expect the stock to go down by more than 1%. Negative Betas, while rare, signify a negative correlation. When the market goes up, we would expect the stock price to go down.

For readers with a background in regression analysis, Beta is the slope of the linear regression shown in the formula below, where Returns are the return on an individual stock or portfolio, Rf is the risk free rate, RMarket is the return on a market portfolio, and e is an error term.

## Formula

Beta is the BetaMarket derived from the regression below:

Returns - Rf = Alpha + BetaMarket x (RMarket - Rf) + e

Where:

Rf is the risk free rate for a given month (YCharts uses the 4 Week Average T-Bill (Monthly))

RMarket is the market return for a given month (YCharts uses the S&P 500 Total Returns Index SPXTR)

When calculating, we use the maximum of 60 months of historical returns data or the full life of returns data of the stock. There must be at least 36 months of data for us to run this calculation.

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