Can someone explain the Security Market Line and how to tell if a stock is overvalued or undervalued using CAPM?

Question

AcadiFi · Accepted Answer

The Security Market Line (SML) is the graphical representation of CAPM. It shows the relationship between **systematic risk (beta)** on the X-axis and **expected return** on the Y-axis. ```mermaid graph TD subgraph Security Market Line direction LR RF[Rf = 4.0%
Beta = 0] ---|SML slope = Market Risk Premium 6%| MKT[Market Portfolio
E Rm = 10%, Beta = 1.0] MKT ---|SML continues| HIGH[High Beta Zone
Beta > 1.0] end A[Stock A: Beta 0.8
Actual Return 9.5%
ABOVE SML = Undervalued] -.-> |Positive Alpha| SML_A[Required: 8.8%] B[Stock B: Beta 1.2
Actual Return 10.0%
BELOW SML = Overvalued] -.-> |Negative Alpha| SML_B[Required: 11.2%] C[Stock C: Beta 1.0
Actual Return 10.0%
ON SML = Fairly Valued] -.-> |Zero Alpha| MKT ``` **The CAPM Formula:** E(R_i) = R_f + Beta_i x (E(R_m) - R_f) Where: - R_f = Risk-free rate - Beta_i = Sensitivity of the stock to market movements - E(R_m) - R_f = Market risk premium (MRP) **Worked Example:** Assume R_f = 4.0% and E(R_m) = 10.0%, so MRP = 6.0%. Consider three stocks at Ridgeline Capital: | Stock | Beta | CAPM Required Return | Actual Expected Return | Alpha | Verdict | |---|---|---|---|---|---| | Ashford Tech | 0.80 | 4% + 0.80(6%) = **8.80%** | 9.50% | +0.70% | Undervalued (buy) | | Baxter Energy | 1.20 | 4% + 1.20(6%) = **11.20%** | 10.00% | -1.20% | Overvalued (sell) | | Caldwell Retail | 1.00 | 4% + 1.00(6%) = **10.00%** | 10.00% | 0.00% | Fairly valued (hold) | **How to Read the SML Graph:** 1. **On the SML** — The security offers exactly the return predicted by CAPM for its level of beta. Alpha = 0. It is fairly priced. 2. **Above the SML** — The security offers *more* return than CAPM requires. Positive alpha. It is undervalued — you are getting excess return for the risk. **Buy signal.** 3. **Below the SML** — The security offers *less* return than CAPM requires. Negative alpha. It is overvalued — you are not being adequately compensated for the risk. **Sell signal.** **Key Distinctions for the Exam:** - The SML uses **beta** (systematic risk only) on the X-axis, not total risk (standard deviation). This is different from the Capital Market Line (CML), which uses total risk. - A stock can have high total risk (volatile) but low beta if much of its volatility is unsystematic (diversifiable). - CAPM assumes investors hold the market portfolio, so only systematic risk is priced. **Common Pitfall:** Students confuse SML with CML. The CML applies to *efficient portfolios* (combinations of the risk-free asset and market portfolio). The SML applies to *any individual security or portfolio* — it prices systematic risk for everything. Test your SML intuition with our CFA Level I Portfolio Management practice questions.

Can someone explain the Security Market Line and how to tell if a stock is overvalued or undervalued using CAPM?

Master Level I with our CFA Course

Related Questions

Practice Questions