Capital Asset Pricing Model
Model describing relationship between systematic risk and expected return for assets in equilibrium.
The Capital Asset Pricing Model (CAPM), developed by William Sharpe, John Lintner, and Jan Mossin in the 1960s building on Harry Markowitz's portfolio theory, describes the relationship between systematic risk (beta) and expected return for assets in an efficient market. The CAPM formula is: Expected Return = Risk-Free Rate + Beta × (Market Return − Risk-Free Rate). The term (Market Return − Risk-Free Rate) is called the equity risk premium (ERP), representing the excess return investors demand for taking on market risk. CAPM implies that investors should only be compensated for bearing systematic risk (risk that cannot be diversified away), not idiosyncratic risk (company-specific risk), because rational investors will hold diversified portfolios that eliminate idiosyncratic risk. This framework is used extensively in corporate finance to estimate the cost of equity capital via the Weighted Average Cost of Capital (WACC), in asset valuation through discounted cash flow (DCF) models, and in evaluating whether realized returns justify the risk taken (Jensen's Alpha). Empirical tests of CAPM have found persistent anomalies—small-cap stocks and value stocks have historically delivered returns above what CAPM predicts—leading to multi-factor models like the Fama-French Three-Factor Model, which adds size and value factors to beta. The CAPM's assumptions include: frictionless markets, unlimited borrowing at the risk-free rate, identical investor expectations, and mean-variance utility. While these simplifications make the model tractable, they limit its real-world accuracy. Despite empirical shortcomings, CAPM remains the foundational model for understanding risk-return tradeoffs and is taught in every finance curriculum worldwide.
FAQs
How is CAPM used in corporate finance?
CAPM is primarily used to estimate the cost of equity capital, which feeds into the WACC calculation. By estimating a company's beta relative to the market and combining it with the risk-free rate and equity risk premium, analysts derive the return equity investors require—a key input to DCF valuations.
What is the equity risk premium in CAPM?
The equity risk premium (ERP) is the excess return of the market above the risk-free rate—the compensation investors demand for holding risky equities instead of risk-free assets like government bonds. Historically the ERP has been approximately 4–6% in US markets, though estimates vary widely.
Why has CAPM been challenged by empirical research?
Studies have found that small-cap and value stocks generate returns that CAPM cannot explain, leading to the Fama-French multi-factor model. CAPM also predicts a positive return-risk relationship across stocks that empirical data does not consistently support, suggesting factors beyond beta influence returns.
Related Terms
Beta
Measure of an investment's volatility relative to the overall market or benchmark index.
Modern Portfolio Theory
Framework for constructing investment portfolios to maximize return for a given level of risk.
Efficient Frontier
Set of optimal portfolios offering highest expected return for each level of portfolio risk.
Weighted Average Cost of Capital
The blended rate of return required by all of a company's capital providers — debt and equity — weighted by their proportions, used as the discount rate in valuation.
