CAPM, the Security Market Line, Expected Return, and Applications

Updated for the 2026-2027 CFA® Level I curriculum.

The capital asset pricing model explains how expected return relates to systematic risk. It gives you one equation to find the return investors require for holding a risky asset. Level I tests this concept through direct calculations, graph interpretation, and valuation questions using the security market line. Understanding CAPM also sets up later readings on portfolio performance evaluation.

Key Takeaways About CAPM, the Security Market Line, Expected Return, and Applications

• CAPM links expected return to systematic risk only, measured by beta, not total risk.

• The formula is , where is the market risk premium.

• The security market line (SML) graphs this equation. Every fairly priced asset sits on the line.

• A security plotting above the SML is undervalued. One plotting below is overvalued.

• Alpha measures the gap between a security's estimated return and its CAPM-required return.

• CAPM rests on several unrealistic assumptions, which explains why the model has known limitations.

What You Need to Know for CFA Level I

• Memorize the CAPM formula and know each input by name, not just by symbol.

• Be able to calculate required return given a risk-free rate, market return, and beta.

• Know the CAPM assumptions well enough to identify which one a question is testing.

• Understand why beta, not standard deviation, is the correct risk measure in this model.

• Be able to plot or interpret a security's position relative to the SML.

• Know the difference between the SML and the capital market line (CML).

• Recognize CAPM's practical uses and its main limitations.

CAPM Assumptions

CAPM rests on a set of simplifying assumptions. The model's conclusions only hold if these assumptions are true, which is part of why CAPM has real-world limitations.

Exam questions often describe a scenario that violates one of these assumptions, such as an investor who cannot borrow at the risk-free rate, and ask what breaks down as a result.

Expected or Required Return Equation

CAPM's core output is the required return, the minimum return an investor should accept given an asset's systematic risk.

Where:

• = expected or required return on asset

• = risk-free rate

• = beta of asset , a measure of systematic risk relative to the market

• = expected return on the market portfolio

• = market risk premium

Plain-English interpretation: Required return starts with the risk-free rate, then adds compensation for systematic risk. That compensation equals beta multiplied by the market risk premium. A higher beta means more systematic risk and a higher required return.

Market Risk Premium and Beta

The market risk premium, , is the extra return investors expect for holding the market portfolio instead of a risk-free asset. It applies to the whole market, not to any single security.

Beta scales that premium to a specific asset. A beta of 1.0 means the asset's systematic risk matches the market. A beta above 1.0 means the asset amplifies market moves. A beta below 1.0 means the asset dampens them.

A common exam trap uses total market return instead of the market risk premium. Always subtract the risk-free rate from the expected market return before multiplying by beta.

The Security Market Line

The security market line is the graphical version of the CAPM equation. It plots expected return on the y-axis against beta on the x-axis. The line starts at the risk-free rate when beta equals zero and rises with a slope equal to the market risk premium.

Every security that is fairly priced under CAPM sits exactly on the SML. The line represents the required return for any level of systematic risk, so it applies to individual securities and portfolios, not just efficient combinations.

SML vs. CML

Candidates frequently confuse the SML with the capital market line. They measure different types of risk and apply to different assets.

Overvalued and Undervalued Interpretation

Plotting an asset relative to the SML tells you whether the market has priced it correctly.

• If a security's estimated return is above the SML, it is undervalued. Investors expect more return than the systematic risk requires, so demand should push the price up until the return falls back to the required level.

• If a security's estimated return is below the SML, it is overvalued. Investors expect less return than the risk requires, so the price should fall.

Alpha captures this gap numerically:

A positive alpha signals undervaluation. A negative alpha signals overvaluation. This is one of the most reversed concepts on the exam, so anchor it to the idea that higher-than-required return means the asset is cheap relative to its risk.

Applications and Limitations

CAPM shows up across the curriculum, not just in this reading.

Common applications:

• Estimating the cost of equity for valuation models

• Setting a hurdle rate for capital budgeting decisions

• Evaluating whether a security or portfolio has generated alpha

• Serving as the benchmark return in performance evaluation measures like Jensen's alpha

Key limitations:

• CAPM assumes a single risk factor, beta, while real returns often depend on multiple factors.

• The assumptions, such as frictionless markets and unlimited borrowing at the risk-free rate, do not hold in practice.

• Beta estimates change over time and depend on the data period and index used.

• The model is forward-looking in theory, but analysts often test it using historical data, which creates a mismatch.

Worked Example

Scenario: An analyst is evaluating Colton Robotics, a mid-cap manufacturer. The risk-free rate is 3%, and the expected return on the market portfolio is 9%. Colton Robotics has a beta of 1.2. Based on the company's growth outlook, the analyst forecasts an expected return of 12%.

Step 1: Find the market risk premium.

Step 2: Calculate the CAPM required return.

Step 3: Compare the estimated return to the required return.

Colton Robotics has a positive alpha of 1.8%. Its estimated return sits above the SML for its beta of 1.2. Based on this analysis, the stock is undervalued. The analyst would expect the price to rise as the market corrects toward the required return.

Common Exam Traps

• Using standard deviation instead of beta. CAPM measures only systematic risk. Standard deviation captures total risk and belongs to the CML, not the SML.

• Confusing the SML with the CML. The SML uses beta and applies to any asset. The CML uses standard deviation and applies only to efficient portfolios.

• Using the total market return instead of the market risk premium. Always subtract the risk-free rate from the expected market return before multiplying by beta.

• Reversing overvalued and undervalued interpretations. A return above the SML means undervalued, not overvalued. Tie this back to alpha: positive alpha means undervalued.

• Forgetting single-period assumptions apply. CAPM assumes one holding period. Questions describing multi-period cash flows may be testing a different model.

Practice Questions

An analyst estimates the following inputs for a stock:

• Risk-free rate: 4%

• Expected return on the market: 10%

• Stock beta: 0.8

• Analyst's forecasted return for the stock: 9%

Based on CAPM, the stock is best described as:

1. Undervalued

2. Overvalued

3. Fairly valued

FAQs About CAPM, the Security Market Line, Expected Return, and Applications