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Security Market Line (SML) Definition and Characteristics


The Security Market Line (SML) is a graphical representation of the expected return for a particular security or portfolio in relation to the systematic risk, or beta, it possesses. In this context, it showcases the trade-off between risk and expected return. The SML is a vital component in the Capital Asset Pricing Model (CAPM), helping investors determine the appropriate required return for various levels of risk.


Phonetics for the keyword: Security Market Line (SML) Definition and Characteristics- Security: /sɪˈkjʊrɪti/- Market: /ˈmɑːrkɪt/- Line: /laɪn/- SML: /ˌɛsˌɛmˈɛl/- Definition: /ˌdɛfɪˈnɪʃən/- and: /ænd/- Characteristics: /ˌkærəktəˈrɪstɪks/

Key Takeaways

  1. Definition: The Security Market Line (SML) is a graphical representation of the relationship between a financial asset’s expected return and its beta (systematic risk) with respect to the market portfolio. It is used to analyze investments and determine if they offer a fair return based on their level of risk.
  2. Capital Asset Pricing Model (CAPM): The SML is derived from the CAPM, an essential model in modern portfolio theory. CAPM expresses the expected return of an individual asset as a function of the risk-free rate, the asset’s beta, and the expected return of the market portfolio. This model helps investors understand the trade-off between risk and return and enables them to make decisions on whether an asset is undervalued, overvalued, or fairly priced.
  3. Characteristics: The SML has the following characteristics:
    • It is a straight line sloping upward, starting from the risk-free rate. This shows that assets with higher risk (beta) will have a higher expected return.
    • It represents the expected return for any given level of systematic risk.
    • Assets that plot above the SML are considered undervalued, as they offer higher returns for their risk levels. Conversely, assets that plot below the SML are considered overvalued because their returns are lower than their risk levels.


The Security Market Line (SML) is important in business and finance because it plays a crucial role in understanding the relationship between risk and expected return for individual investments within the context of a diversified portfolio. It represents a graphical depiction of the Capital Asset Pricing Model (CAPM), which allows investors to evaluate the pricing of various securities by taking into account their systematic risk, or beta, relative to the overall market. This information helps investors make informed investment decisions by comparing the performance of a security against its expected return given its level of risk, as well as the overall market performance. By making use of the SML, investors can better diversify their portfolios, mitigate risk, and optimize returns, contributing to overall financial market efficiency.


The Security Market Line (SML) serves a critical purpose in the world of finance and portfolio management, as it aims to assess and display the relationship between the risk or systematic risk (beta) and expected return of different assets or investment securities. By achieving this, the SML is instrumental in enabling investors, portfolio managers, and financial analysts to evaluate investment opportunities more accurately and make informed decisions based on anticipated returns and risk exposure. The SML plays an essential role in portfolio diversification, as it helps investors to identify optimal combinations of risky and stable assets to maximize returns and minimize the variability of investment results.

Essentially, the SML is a tool used within the context of the Capital Asset Pricing Model (CAPM), which is a widely utilized theoretical model for predicting the expected return of an asset given its risk level. The SML graphically depicts how the CAPM formula calculates the expected return: by adding the risk-free rate to the product of the asset’s beta (a measure of the asset’s sensitivity to market movements) and the risk premium (the difference between the overall market return and the risk-free rate). This allows investors to compare various investment options and identify where they lie on the SML, thus shedding light on whether an investment is overpriced, fairly priced, or undervalued. In summary, the Security Market Line is a vital tool for investors and financial experts to understand the risk-return relationship and optimize their financial investment decisions.


The Security Market Line (SML) is a graphical depiction of the Capital Asset Pricing Model (CAPM), which illustrates the relationship between the expected return and the risk of various securities or portfolios within a market. The SML helps investors make decisions based on the trade-off between the risk and expected returns of different investments. Here are three real-world examples of the SML in action:

1. Portfolio Diversification: A professional fund manager seeks to create a well-diversified portfolio of stocks for her clients. Using the SML, she can analyze various stocks in terms of their individual risk (measured through beta) and expected returns, allowing her to select those that plot along or above the SML. This way, the fund manager can optimize the portfolio’s performance and ensure her clients receive a desirable return on investment that takes the appropriate level of risk into account.

2. Evaluating Stock Performance: Consider an individual investor who wants to evaluate and compare different stocks before making an investment decision. By plotting each stock onto the SML, the investor can see if a specific stock or group of stocks is underperforming, overperforming, or accurately priced based on their risk levels. For instance, stocks that fall below the SML may indicate that they are overpriced given their risk levels, while those above the SML may reflect that they are undervalued or offering higher returns given their risk levels.

3. Investment Strategy Analysis: A financial analyst working at an investment research firm is tasked with formulating investment strategies for clients based on various market conditions and economic indicators. By analyzing historical data and trends, the analyst can study how different securities and portfolios have behaved in correlation to the SML. This knowledge enables him to determine which assets perform best under different market conditions and recommend investment strategies to clients that maximize returns while staying within their risk tolerance levels.

Frequently Asked Questions(FAQ)

What is the Security Market Line (SML)?

The Security Market Line (SML) is a graphical representation of the Capital Asset Pricing Model (CAPM) that plots the expected return of a security or a financial asset as a function of its systematic risk, also known as beta. It demonstrates the trade-off between risk and return in the market, where higher risk demands a higher expected return.

What are the main components of the SML?

The main components of the SML are the risk-free rate (vertical intercept), beta (slope), and the market risk premium (the difference between the expected return on the market portfolio and the risk-free rate).

What is the significance of the slope of the SML?

The slope of the SML indicates the market risk premium. It shows the additional return an investor can expect for holding a diversified portfolio of risky assets as opposed to holding a risk-free asset. A steeper slope indicates higher market risk premium, while a flatter slope indicates a lower market risk premium.

How is beta measured in the Security Market Line?

Beta measures the sensitivity of an individual security’s return to the overall market return. A beta of 1 indicates that the security moves in sync with the market, while a beta greater than 1 suggests that the security is more volatile than the market. Conversely, a beta less than 1 indicates that the security is less volatile than the market.

How can the SML be used in portfolio management?

The SML can be used to evaluate the risk and return relationship of individual securities and determine whether they are fairly priced. Securities that plot above the SML are considered undervalued since they offer a higher return for a given level of risk, while those below the SML are overvalued as they provide a lower return for their risk level. This analysis helps investors in making informed decisions about their portfolio composition and asset allocation.

What is the difference between the Security Market Line (SML) and the Capital Market Line (CML)?

The SML represents the relationship between beta and expected return for individual securities or portfolios, while the CML indicates the relationship between the risk (standard deviation) and expected return for efficient portfolios. Additionally, the SML relies on the concept of systematic risk measured by beta, whereas the CML is based on the total risk of a portfolio.

Are there any limitations to the Security Market Line?

Yes, there are some limitations to the SML, such as relying on past data for beta calculations, which may not necessarily predict future stock behavior. It also depends on the assumptions of the CAPM, like investors being rational and risk-averse, markets being efficient, and no transaction costs or taxes, which may not always hold true in real-world scenarios.

Related Finance Terms

  • Capital Asset Pricing Model (CAPM): A key finance concept that allows the calculation of the expected return of a security or a portfolio, utilizing the risk-free rate, beta coefficient, and market risk premium along with the Security Market Line.
  • Beta Coefficient: A measure of a security or portfolio’s sensitivity to market fluctuations, or systematic risk, in comparison to the overall market. Higher beta values indicate greater volatility and risk, while the market itself typically has a beta of 1.
  • Market Risk Premium: The expected return on the market portfolio above and beyond the risk-free rate, representing the additional return investors expect to receive for taking on systematic risk associated with the market.
  • Risk-Free Rate: The return on a virtually risk-free investment instrument, such as short-term government securities like treasury bills. The risk-free rate serves as the starting point for the Security Market Line, as the intercept term in the SML equation.
  • Systematic Risk: Non-diversifiable risk attributed to overarching market factors, such as interest rates, economic conditions, and political events, that affect all securities in the market. The Security Market Line serves to make a distinction between securities with different levels of exposure to this systematic risk.

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