The Capital Asset Pricing Model (CAPM) estimates the return an investor should expect from an asset by starting with a risk-free baseline, then adding a premium scaled to how much that asset moves with the broader market. The formula is: Expected Return = Risk-Free Rate + Beta × (Market Return − Risk-Free Rate). It was developed independently in the 1960s by William Sharpe, Jack Treynor, John Lintner, and Jan Mossin, and it remains the standard tool for pricing equity risk, setting corporate hurdle rates, and judging whether a portfolio manager earned their fee.
What Each Variable Means
Written in symbols, the equation is E(Ri) = Rf + βi × (E(Rm) − Rf). Four inputs do all the work.
The risk-free rate (Rf) is what you’d earn on an investment with essentially no default risk. Analysts use U.S. Treasury yields as the proxy. The 10-year Treasury Note is the usual choice for equity work because its maturity roughly matches the horizon of a long-term stock investor. In early 2026 the 10-year yield has been hovering around 4.2%, moving with Federal Reserve policy and inflation expectations.1U.S. Department of the Treasury. Daily Treasury Par Yield Curve Rates Some analysts prefer the 3-month Treasury bill for short-horizon work. The choice of maturity shifts your baseline and ripples through the entire calculation.
The expected market return (E(Rm)) is what you think the overall stock market will deliver. Most practitioners use the S&P 500 as the stand-in. Since 1957, the index has averaged roughly 10% per year in nominal terms, counting price gains and reinvested dividends.
The market risk premium (E(Rm) − Rf) is the gap between those two numbers. It’s the extra return investors collectively demand for owning stocks instead of Treasuries. As of January 2026, NYU finance professor Aswath Damodaran estimates the implied equity risk premium for the U.S. market at 4.23%, a figure derived from current prices and expected future cash flows rather than long-run historical averages.2NYU Stern. Data Update 2 for 2026: A Testing Year for US Equities A historical premium is often 5% to 6%. Which one you use is a judgment call, and it can meaningfully change the output.
The last input, beta (βi), is the piece specific to the individual investment. It gets its own section below.
Understanding Beta
Beta measures how a stock’s price moves relative to the broader market. It captures systematic risk, the market-wide risk that holding more stocks won’t eliminate. Analysts compute it by regressing the stock’s returns against the index’s returns, usually over three to five years of weekly or monthly data. The slope of the best-fit line is beta.
The values read like this:
- Beta of 1.0 means the stock has tracked the market. A 5% market move corresponds to a roughly 5% move in the stock.
- Beta above 1.0 means the stock has amplified market moves. A 1.5 beta implies about 50% more movement than the market in either direction.
- Beta below 1.0 means the stock has been less reactive. A 0.6 beta implies about 60% as much movement as the market.
- Negative beta is rare and implies the asset tends to move opposite the market. Gold mining stocks sometimes behave this way during downturns.
Sector data shows the pattern clearly. Based on January 2026 figures, internet software sits at 1.69, semiconductors at 1.52, and computers and peripherals at 1.35. On the other end, food processing comes in at 0.61, soft beverages at 0.64, water utilities at 0.41, and general utilities at 0.24.3NYU Stern. Betas by Sector (US) The logic tracks intuition: utilities sell power and water in any economy, while chipmakers rise and fall with business spending and consumer demand.
Most financial data providers publish pre-calculated betas, so you don’t have to run the regression yourself. Be aware that two reputable sources can report noticeably different betas for the same stock, depending on the time window, return frequency, and benchmark index used.
A Worked Example
Say you’re looking at a technology stock with a beta of 1.35. You set the risk-free rate at 4.2% and the expected market return at 10%.
Start with the market risk premium: 10% − 4.2% = 5.8%. Multiply by beta: 1.35 × 5.8% = 7.83%. Add the risk-free rate: 4.2% + 7.83% = 12.03%.
CAPM says a rational investor should demand about 12% a year to hold this stock. If your own research suggests the stock will actually return 14%, the model flags it as underpriced. If you only expect 9%, the stock isn’t paying you enough for the risk, and your money has better uses.
That comparison is the whole point of the exercise. CAPM doesn’t predict what the market will do. It tells you what the market should offer if risk is priced correctly, and lets you measure individual securities against that benchmark.
Reading the Security Market Line
The Security Market Line (SML) is CAPM drawn as a graph. Put beta on the horizontal axis and expected return on the vertical axis. The line starts at the risk-free rate where beta is zero, passes through the market return where beta is one, and continues upward from there.
Every correctly priced security should sit on that line. A stock plotted above the SML is paying more than its beta warrants, which makes it a potential buy. A stock below the line is paying too little for the risk, which makes it a candidate to sell. In a perfectly efficient market, nothing would ever sit off the line. Real stocks deviate constantly, which either reflects genuine mispricing or signals that beta alone misses something important about risk.
How CAPM Is Used in Corporate Finance
Cost of Equity and WACC
CAPM’s most consequential use happens inside companies rather than in stock picking. When a firm needs to know what return its shareholders expect, CAPM supplies the number. That cost of equity then feeds into the Weighted Average Cost of Capital (WACC), which blends equity and debt costs according to the company’s capital structure.4Wharton School of the University of Pennsylvania. Applying the CAPM to Capital Budgeting
WACC becomes the discount rate used to value the company’s future cash flows. A higher WACC makes future earnings worth less today, which lowers the company’s estimated value. For a large firm, moving the cost of equity by a single percentage point can shift a valuation by billions.
Hurdle Rates for Projects
Companies also use CAPM-derived rates to decide whether a project is worth doing. If the expected return on a new factory or product line doesn’t clear the rate CAPM assigns to that level of risk, the firm is better off returning the cash to shareholders, who can earn the same return at the same risk level in the open market.
A detail that matters here: when the project sits inside the company’s existing business, the company’s own beta is the right input. When the project is in a different industry, the company’s historical beta is irrelevant, and the beta of the target industry should be used instead. Using the wrong beta sets the bar too low or too high and leads directly to value-destroying investments or missed opportunities.4Wharton School of the University of Pennsylvania. Applying the CAPM to Capital Budgeting
Judging Portfolio Managers With Alpha
Jensen’s alpha runs CAPM in reverse. Instead of asking what return an asset should earn, it compares what a portfolio actually earned against what CAPM predicted, and treats the difference as the manager’s contribution.5CFA Institute. Measures of Risk-Adjusted Return: Let’s Not Forget Treynor and Jensen
The formula is: Alpha = (Portfolio Return − Risk-Free Rate) − Beta × (Market Return − Risk-Free Rate).
A positive alpha means the manager delivered more than CAPM says the risk justified. A negative alpha means the manager underperformed on a risk-adjusted basis, which matters most when the investor is paying active-management fees. Michael Jensen introduced the measure in 1968, and it remains the standard way to grade a fund manager. The verdict depends on CAPM being the right benchmark in the first place, which is where the model’s problems come in.
Where the Model Falls Short
CAPM is elegant and easy to teach. It also has a long record of empirical failures that any serious user should know about.
Higher beta hasn’t actually produced higher returns. CAPM’s central prediction is that riskier (higher-beta) stocks should pay more. The data pushes back. A study covering January 1968 through December 2008 found that a dollar invested in the lowest-beta stocks grew to $60.46, while a dollar in the highest-beta stocks grew to just $3.77.6NYU Stern. Benchmarks as Limits to Arbitrage: Understanding the Low-Volatility Anomaly Over that stretch, the relationship between beta and return was inverted. Researchers attribute part of this to behavioral biases, with some investors treating high-beta stocks like lottery tickets and overpaying for upside, and part to institutional pressures that discourage benchmarked fund managers from loading up on cheap but boring low-beta names.
Beta explains less than CAPM suggests. Fama and French’s 1992 study found that once you sort stocks by beta, the relationship with actual returns is essentially flat. Size (small companies outperforming large ones) and book-to-market ratio (value stocks outperforming growth) did a far better job explaining returns than beta did.7Tuck School of Business at Dartmouth. The Capital Asset Pricing Model: Theory and Evidence
The “market” in the formula isn’t observable. Richard Roll argued in 1977 that CAPM has never been properly tested. The market portfolio is supposed to contain every investable asset, including stocks, bonds, real estate, private businesses, and human capital. The S&P 500 isn’t that. When a test fails, there’s no way to tell whether CAPM is wrong or whether the proxy is.7Tuck School of Business at Dartmouth. The Capital Asset Pricing Model: Theory and Evidence
Beta itself drifts. A stock’s beta over the past three years can differ substantially from its beta over the past five, or from its beta in the next three. S&P Dow Jones Indices research on high-beta strategies found that performance in live trading diverged from backtests partly because the stocks flagged as high-beta in one window didn’t keep that sensitivity in the next.8S&P Dow Jones Indices. Low Volatility and High Beta: A Study in Backtest Integrity For a model that leans so heavily on one variable, that instability is a real practical problem.
CAPM also rests on idealized conditions no real market meets: no transaction costs, no taxes, identical information for everyone, unlimited borrowing and lending at the risk-free rate, and no investor large enough to move prices. Each gap between those assumptions and reality chips at the model’s accuracy.
Alternatives and Why CAPM Persists
The empirical gaps drove the development of multi-factor models. The Fama-French three-factor model keeps CAPM’s market factor and adds two more:9Kenneth R. French – Data Library. Description of Fama/French Factors
- SMB (Small Minus Big) captures the historical return gap between small-cap and large-cap stocks.
- HML (High Minus Low) captures the historical return gap between value stocks and growth stocks.
In 2015, Fama and French added two more factors, profitability and investment, producing a five-factor model. Each additional factor explains more of the historical variation in returns.
None of these have fully replaced CAPM. The single-factor version has one real advantage: simplicity. It needs one company-specific input instead of five, and it’s far easier to explain to a client or a board. Most corporate finance textbooks still teach CAPM as the default cost-of-equity calculation, and most practitioners still use it, often as a starting point they adjust from there. Whether the multi-factor models predict future returns any better than CAPM, or merely describe past ones more accurately, is still being argued in the academic literature.