Boundless Finance: "Chapter 10, Section 3, Part 1: "
The Capital Asset Pricing Model
The capital asset pricing model (CAPM) allows us to price risky securities in order to determine if an investment should be undertaken.
LEARNING OBJECTIVE

Calculate a company's expected rate of return using the Capital Asset Pricing Model (CAPM)
KEY POINTS
 CAPM determines the expected rate of return of an asset.
 The model takes into account the asset's sensitivity to systematic risk (beta), the expected return of the market, and the expected return of a riskfree asset.
 CAPM states that investors are only rewarded for bearing systematic risk.
 CAPM states that if the expected return is not greater than or equal to our required return the investment should not be made.
TERMS
 Unsystematic risk
Risk peculiar to an asset, which can be eliminated through diversification.
 systematic risk
The risk associated with an asset that is correlated with the risk of asset markets generally, often measured as its beta.
 beta
Average sensitivity of a security's price to overall securities market prices.
EXAMPLE
 The current riskfree rate is 5%. The market is expected to return 12% next year. The beta of the security is 1.9. Expected return = 5% + 1.9*(12%  5%). Expected return = 18.3%. If 18.3% is greater than or equal to the return we require, the investment should be undertaken.
FULL TEXT
The Capital Asset Pricing Model (CAPM)
The capital asset pricing model is a financial model, used to price risky securities, that describes the relationship between risk and expected return. It determines what the rate of return of an asset will be, assuming it is to be added to an already welldiversified portfolio, given that asset's systematic risk. The model takes into account the asset's sensitivity to market fluctuations, often represented by the quantity beta (β), as well as the expected return of the market and the expected return of a theoretical riskfree asset .
CAPM Equation
The expected rate of return = the rate of return for a riskfree asset + beta* (the rate of return of the market  the riskfree rate). The return of the market minus the riskfree rate is also known as the risk premium.
CAPM assumes that every asset is correctly priced. In real world applications, it enables us to determine whether or not a security is a worthwhile investment by comparing the expected rate of return of the security, given by the CAPM equation, with the actual rate of return. If the actual return is greater than or equal to what we expect from CAPM, then the investment should be undertaken.
Assumptions of CAPM
All investors:
 Aim to maximize economic utilities.
 Are rational and riskaverse.
 Are broadly diversified across a range of investments.
 Are price takers, i.e., they cannot influence prices.
 Can lend and borrow unlimited amounts under the riskfree rate of interest.
 Trade without transaction or taxation costs.
 Deal with securities that are all highly divisible into small parcels.
 Assume all information is available at the same time to all investors.
Further, the model assumes that past returns will effectively predict the future risk associated with a given security.
Systematic vs. Unsystematic Risk
Systematic risk  also called market risk or nondiversifiable risk  represents the risk present in a security in relation to the economy as a whole. Unsystematic risk  also called idiosyncratic risk or diversifiable risk  represents the risk present in a security that is specific to that investment and unrelated to the overall risk of the market .
Systematic vs. Unsystematic Risk
As the number of stocks in a portfolio increase, the amount of unsystematic risk approaches zero. However, it is impossible to remove systematic risk, as it concerns the economy in general.
CAPM states that in market equilibrium, investors are only rewarded for bearing systematic risk  the type of risk that cannot be diversiﬁed away. Investors should not be rewarded for bearing unsystematic risk, since this uncertainty can be mitigated through appropriate diversiﬁcation.