CAPM, the Capital Asset Pricing Model, calculates the expected return on an investment based on its risk. More specifically, it gives you a single number: the minimum return you should expect from a stock or other asset, given how risky it is compared to the overall market. If the expected return falls below that number, the investment isn’t worth the risk.
The Core Idea Behind CAPM
Every investment carries some level of risk. A U.S. Treasury bond is about as safe as it gets, so it pays a relatively low return. A volatile tech stock could lose half its value in a year, so investors need the promise of higher returns to justify owning it. CAPM puts that intuition into a formula: the riskier the investment, the higher the return it needs to deliver.
The model focuses on one specific type of risk called systematic risk, which is the risk that comes from broad market forces like recessions, interest rate changes, or geopolitical events. You can’t diversify this risk away by holding more stocks. CAPM ignores risks unique to individual companies (a CEO scandal, a product recall) because, in theory, a well-diversified portfolio eliminates those. The only risk that earns you extra return, according to CAPM, is your exposure to the market as a whole.
How the Formula Works
The CAPM formula looks like this:
Expected Return = Risk-Free Rate + Beta × (Market Return − Risk-Free Rate)
Each piece does something specific:
- Risk-free rate: The return you’d earn on a virtually risk-free investment, typically a U.S. Treasury bond. This compensates you for the time value of money, the simple fact that a dollar today is worth more than a dollar next year. As of early 2026, the 10-year Treasury yield sits around 4.05%.
- Beta: A measure of how sensitive an investment is to market movements. A beta of 1 means the asset moves in lockstep with the market. A beta of 1.5 means it swings 50% more than the market in either direction. A beta of 0 means the asset has no exposure to market risk at all.
- Market return minus risk-free rate: This is called the equity risk premium, the extra return investors demand for owning stocks instead of safe bonds. NYU Stern estimates the current U.S. equity risk premium at roughly 4.5%.
A Quick Example
Say you’re evaluating a stock with a beta of 1.3. Using current figures, you’d plug in a risk-free rate of about 4%, a market risk premium of about 4.5%, and calculate:
Expected Return = 4% + 1.3 × 4.5% = 4% + 5.85% = 9.85%
That 9.85% is your benchmark. If your analysis suggests the stock will return 12%, it looks like a good deal because you’re being compensated above what CAPM says you need. If it’s only expected to return 7%, you’re taking on more risk than you’re being paid for.
What Businesses Use CAPM For
Individual investors sometimes use CAPM to evaluate stocks, but its biggest practical application is in corporate finance. Companies use the formula to calculate their cost of equity, which is the return shareholders expect in exchange for investing in the company. This number feeds into a company’s overall cost of capital.
That cost of capital becomes the hurdle rate for new projects. When a company considers building a new factory, launching a product line, or acquiring another business, it compares the project’s projected return against the hurdle rate. If the project can’t clear that bar, it doesn’t get funded. CAPM gives companies a systematic way to set that bar rather than guessing.
Investment banks and analysts also rely on CAPM when building stock valuation models. The expected return from CAPM serves as the discount rate for projecting what a company’s future cash flows are worth today. A higher discount rate means future earnings are worth less in present terms, which lowers the stock’s estimated fair value.
The Security Market Line
CAPM has a visual representation called the Security Market Line, or SML. It’s a graph where the horizontal axis shows beta and the vertical axis shows expected return. The line starts at the risk-free rate (where beta equals zero) and slopes upward. The steepness of that slope is the equity risk premium.
Any investment sitting above the line is theoretically undervalued because it offers more return than its risk level demands. Anything below the line is overvalued. Portfolio managers use this visual shorthand to quickly spot whether an asset’s return justifies its risk.
Where CAPM Falls Short
CAPM is elegant, but it rests on assumptions that don’t hold up perfectly in the real world. The model assumes all investors have identical expectations about returns, that everyone can borrow and lend at the same risk-free rate, and that investors only care about the average return and volatility of their portfolio over a single time period. None of that is strictly true.
The bigger issue is predictive accuracy. Research comparing CAPM’s predictions to actual stock returns has found the model explains only about 3% of the differences in returns across individual stocks. That’s not much. The Fama-French three-factor model, which adds company size and valuation as additional risk factors, does somewhat better but still only explains about 5% of return differences. Neither model is a precision tool for predicting what a single stock will do.
CAPM also assumes beta is stable over time, but a company’s sensitivity to market swings can change as its business evolves, its debt levels shift, or its industry goes through cycles. A beta calculated from the past five years of data may not reflect the next five years of risk.
Why It Still Matters
Despite its limitations, CAPM remains the most widely used model for estimating expected returns in practice. Most financial analysts default to it when pricing individual stocks, largely because it’s simple and requires only three inputs. Multi-factor models offer marginal improvements in accuracy but add complexity that isn’t always justified for everyday analysis.
The real value of CAPM isn’t in producing a perfectly accurate number. It’s in forcing a disciplined framework: before you invest in something risky, you quantify how much extra return that risk should earn you. If an investment can’t clear that threshold, you have a concrete, numerical reason to walk away.