CAPM: How to Estimate the Cost of Equity
When a company uses equity financing, shareholders expect a return that compensates them for the risk they are taking. But how do you put a number on that expectation? The Capital Asset Pricing Model (CAPM) estimates the required return on a stock based on its sensitivity to market risk.
Key takeaway: CAPM says the required return on a stock equals the risk-free rate plus a premium for market risk, scaled by how volatile the stock is relative to the market.
The CAPM Formula
Re = Rf + B x (Rm - Rf)
- Re: Required return on equity (the cost of equity)
- Rf: Risk-free rate
- B (beta): The stock's sensitivity to market movements
- Rm: Expected return on the market
- Rm - Rf: The equity risk premium, the extra return investors demand for holding stocks instead of risk-free assets
Each input captures a different piece of the risk picture. The risk-free rate sets the floor. The equity risk premium captures what the market as a whole earns above that floor. Beta scales that premium up or down based on the individual stock's risk.
Risk-Free Rate
The risk-free rate is the return on an investment with zero default risk. In practice, analysts use the yield on government bonds, typically the 10-year U.S. Treasury bond.
The logic is straightforward: if you can earn 4% with no risk, any investment that carries risk must offer more than 4% to attract capital. The risk-free rate is the starting point for every required return calculation.
Beta
Beta measures how much a stock moves relative to the overall market. The market itself has a beta of 1.0. A stock with a beta above 1.0 is more volatile than the market, and a stock below 1.0 is less volatile.
| Beta | Meaning |
|---|---|
| 0.5 | Moves half as much as the market |
| 1.0 | Moves in line with the market |
| 1.5 | Moves 50% more than the market |
| 2.0 | Moves twice as much as the market |
If the market drops 10%, a stock with a beta of 1.5 would be expected to drop about 15%. If the market rises 10%, the same stock would be expected to rise about 15%.
Beta is estimated by regressing a stock's historical returns against the market's returns. Financial data providers publish beta estimates for publicly traded companies, so you rarely need to calculate it yourself.
Industries with stable, predictable cash flows (utilities, consumer staples) tend to have betas below 1.0. Industries with cyclical or growth-driven earnings (technology, airlines) tend to have betas above 1.0.
Equity Risk Premium
The equity risk premium is the difference between the expected market return and the risk-free rate. It represents the compensation investors demand for bearing market risk instead of holding risk-free bonds.
If the expected market return is 10% and the risk-free rate is 4%, the equity risk premium is 6%. This number is not directly observable. Analysts estimate it using long-run historical averages (typically 5% to 7% for U.S. equities) or forward-looking models based on current market valuations.
CAPM in Action
A company has a beta of 1.3. The risk-free rate is 4%, and the equity risk premium is 6%.
Re = 4% + 1.3 x 6%
Re = 4% + 7.8%
Re = 11.8%
Equity investors require an 11.8% return to hold this stock. The 4% covers the time value of money (what they could earn risk-free), and the 7.8% compensates for the stock's market risk.
This 11.8% is the cost of equity that goes into the WACC formula. If the company also borrows at 5% with a 25% tax rate and funds itself with 60% equity and 40% debt:
WACC = (0.60 x 11.8%) + (0.40 x 5% x (1 - 0.25))
WACC = 7.08% + 1.50%
WACC = 8.58%
The cost of equity is the largest component of WACC for most companies, which is why getting it right matters.
Comparing Companies
CAPM explains why different companies have different costs of equity even when they face the same risk-free rate and equity risk premium. The difference comes from beta.
Using a 4% risk-free rate and 6% equity risk premium:
| Company | Industry | Beta | Cost of Equity |
|---|---|---|---|
| Utility Co. | Utilities | 0.6 | 7.6% |
| Consumer Corp. | Consumer Staples | 0.9 | 9.4% |
| Industrial Inc. | Manufacturing | 1.2 | 11.2% |
| Tech Ltd. | Technology | 1.6 | 13.6% |
| Biotech Co. | Biotechnology | 2.0 | 16.0% |
The utility company's shareholders require 7.6% because its earnings are stable and regulated. The biotech company's shareholders require 16.0% because its earnings are highly uncertain and sensitive to market swings. Both figures start from the same 4% floor, but beta scales the risk premium based on each company's profile.
A higher cost of equity means a higher hurdle rate for new projects. The biotech company needs its investments to clear 16.0% before they create value for shareholders. The utility company only needs to clear 7.6%.
Limitations
CAPM rests on assumptions that do not perfectly hold in practice:
- Single risk factor. CAPM uses only market risk (beta) to explain required returns. In reality, factors like company size, value characteristics, and momentum also affect stock returns. Multi-factor models like the Fama-French three-factor model address this.
- Backward-looking beta. Beta is estimated from historical data, but a company's risk profile can change. A firm that takes on more debt or enters a new market may have a different beta going forward than what historical data suggests.
- Equity risk premium uncertainty. The ERP is not directly observable, and reasonable estimates range from 4% to 8%. A 2-percentage-point difference in the ERP changes the cost of equity meaningfully.
Despite these limitations, CAPM remains the standard starting point for estimating the cost of equity. It uses only three inputs, which makes it practical for most corporate finance applications, even when those inputs require judgment.
Why CAPM Matters
CAPM connects risk measurement to required returns:
- Cost of equity: CAPM provides the Re input for the WACC formula, which drives capital budgeting and valuation decisions.
- Portfolio management: Investors use CAPM to evaluate whether a stock's expected return compensates for its risk. A stock plotting above the security market line is undervalued; below it is overvalued.
- Performance evaluation: Comparing a portfolio's actual return to its CAPM-predicted return (based on beta) shows whether the manager added value beyond what the market risk exposure would explain.
Conclusion
CAPM estimates the return equity investors require based on the risk-free rate, beta, and the equity risk premium. It gives you the cost of equity, which is typically the largest input in WACC.
For how the cost of equity fits into the overall cost of capital, see our guide on WACC. For the investment decisions that cost of capital drives, see our guide on NPV and IRR.
Build real-world finance skills
Interactive lessons and drills covering the concepts that matter in finance.