Capital asset pricing model
(CAPM).
The capital asset pricing model links the expected rates of return on traded assets with their relative levels of market risk (beta).
The model’s uses include estimating a firm’s market cost of equity from its beta and the prevailing theoretical market risk-free rate of return.
The CAPM assumes a straight-line relationship between the beta of a traded asset and the expected rate of return on the asset.
Expressed as a formula:
Re = Rf + beta x [Rm-Rf]
Where:
Re = return on security.
Rf = theoretical risk free rate of return.
Beta = relative market risk.
Rm = average expected rate of return on the market.
For example where:
Rf = theoretical risk free rate of return = 4%;
Beta = relative market risk = 1.2; and
Rm = average expected rate of return on the market = 9%.
Re = 4% + 1.2 x [9% - 4% = 5%]
= 10%.
This investment requires an expected rate of return of 10%, higher than average rate of return on the market as a whole of only 9%, because its market risk (measured by Beta = 1.2) is greater than the average market risk of only 1.0.
Under the capital asset pricing model only the (undiversifiable) market risk of securities is rewarded with additional returns, because the model assumes that rational market participants have all fully diversified away all specific risk within their investment portfolios.
Use of the CAPM to quantify cost of equity
When the CAPM is used to calculate an estimate of the cost of equity, it is conventionally expressed as:
Ke = Rf + beta x [Rm-Rf]
Where:
Ke = cost of equity.
