Security Market Line

The CAPM Equation — The Foundation of the SML

The Security Market Line is the CAPM equation plotted as a graph. The CAPM equation developed by William Sharpe, John Lintner, and Jan Mossin in the 1960s — building on Harry Markowitz's mean-variance portfolio framework published in The Journal of Finance in 1952 — states that the expected return on any risky asset equals the risk-free rate plus the asset's beta multiplied by the equity risk premium.

Expected return equals the risk-free rate plus beta multiplied by the quantity expected market return minus the risk-free rate.

In graphical form, plotting this equation produces a straight line where the y-intercept equals the risk-free rate — the expected return when beta equals zero — and the slope equals the equity risk premium — the expected market return minus the risk-free rate. Every point on the line corresponds to a specific beta value and its associated required expected return.

The y-intercept at the risk-free rate is economically necessary — a security with zero systematic risk — zero sensitivity to market movements — should earn exactly the risk-free rate in equilibrium, because an investor who holds only that security bears no market risk and therefore deserves no market risk premium. A security at the y-intercept earning more than the risk-free rate would attract unlimited buying pressure that drives its price up until the expected return falls to the risk-free rate. A security at the y-intercept earning less would attract unlimited selling until the price falls and the expected return rises to the risk-free rate.

The slope of the Security Market Line — the equity risk premium — is the market-level compensation for systematic risk. It is the additional return per unit of beta that the market offers investors for bearing market-wide risk. If the risk-free rate is three percent and the expected market return is ten percent, the equity risk premium is seven percent — a beta one security earns seven percent above the risk-free rate as compensation for moving perfectly in tandem with the market, a beta two security earns fourteen percent above the risk-free rate as compensation for moving twice as dramatically as the market, and a beta of zero point five security earns three and a half percent above the risk-free rate.

The Axis Variables — Beta and Expected Return

The horizontal axis of the Security Market Line measures beta — the measure of systematic risk developed by Sharpe that quantifies how sensitively a security's returns respond to movements in the returns of the market portfolio.

A beta of one means the security moves dollar for dollar with the market — when the market rises ten percent, the security is expected to rise approximately ten percent, and when the market falls ten percent, the security is expected to fall approximately ten percent. 

A beta of two means the security amplifies market movements — ten percent market gain implies approximately twenty percent security gain, ten percent market loss implies approximately twenty percent security loss. A beta of zero point five means the security dampens market movements — the security moves only half as much as the market in either direction. 

A beta of zero means no systematic relationship to market movements — the security is uncorrelated with the market. A beta below zero — negative beta — means the security moves in the opposite direction from the market — these securities are extremely rare in the equity universe but exist in some commodity and volatility-related instruments.

The vertical axis of the Security Market Line measures the expected rate of return — the return investors require to hold the security given its level of beta. It is critical to understand that the y-axis measures required return — the compensation demanded by rational investors for bearing the specified level of systematic risk — rather than the actual return that will be realised. Actual returns depend on subsequent price movements that may differ materially from expectations.

The Market Portfolio — The Benchmark Point

The market portfolio sits at the midpoint of the Security Market Line — the single point where beta equals one and the expected return equals the expected market return. The market portfolio is the value-weighted portfolio of all risky assets in the investable universe — in practice approximated by broad market indices such as the S&P 500 for United States equities, the MSCI World Index for global equities, or composite multi-asset benchmarks in multi-asset portfolio applications.

In the CAPM framework, the market portfolio is the efficient portfolio — it offers the highest possible expected return for its level of systematic risk and its Sharpe ratio is the maximum achievable by any combination of risky assets alone. Every rational investor in the CAPM world holds the market portfolio as the risky component of their portfolio, combined in varying proportions with the risk-free asset to achieve their individual desired level of overall portfolio risk — the prescription that produces the Capital Market Line discussed below.

Above and Below the SML — Undervalued and Overvalued Securities

The most examination-critical application of the Security Market Line is the identification of securities that are not on the line — that are priced either below or above their theoretically fair value — and the interpretation of what those positions mean for investment decisions.

A security plotted above the Security Market Line offers an expected return higher than the return required by the CAPM for its level of beta. In equilibrium, no such mispricing should persist — rational investors would buy the underpriced security, driving its price up until the expected return falls back to the SML. In practice, identifying genuinely above-SML securities is the goal of active equity management — finding stocks whose expected returns, properly assessed, exceed what the market requires for their systematic risk exposure.

A security plotted below the Security Market Line offers an expected return lower than the CAPM requires for its level of beta. Such a security is paying investors less than they should demand for the systematic risk they are bearing — it is overpriced relative to fair value. In the CAPM world, rational investors would sell or short such securities, driving prices down until expected returns rise to the SML.

In a perfectly efficient market — where all information is immediately and fully reflected in prices — no security would be above or below the SML for any meaningful period because competitive trading would instantaneously eliminate any mispricing. The Efficient Market Hypothesis, covered in its own entry in this dictionary, addresses how rapidly and completely real markets incorporate information. To the extent markets are imperfectly efficient, opportunities to identify above-SML securities through superior analysis exist — the conceptual foundation of active investment management.

Alpha — The Vertical Distance From the SML

Alpha is the direct quantification of a security's or portfolio's position relative to the Security Market Line — the vertical distance between the security's actual expected or realised return and the return that the SML predicts it should earn given its beta.

A positive alpha means the security generates return above what its systematic risk level requires — it plots above the SML. A zero alpha means the security earns exactly its risk-adjusted required return — it sits exactly on the SML. A negative alpha means the security generates return below its risk-adjusted required return — it plots below the SML.

For portfolio management purposes, alpha is the measure of skill — the additional return earned above what could have been achieved by holding the market portfolio with equivalent systematic risk, measured by Jensen's alpha as discussed in the Risk-Adjusted Return entry of this dictionary. A portfolio manager who consistently generates positive alpha is adding value through security selection — identifying securities above the SML, purchasing them before the market recognises and corrects the mispricing, and earning the superior returns those securities provide.

The SML Versus the Capital Market Line — The Critical Distinction

The Security Market Line and the Capital Market Line are both straight lines derived from the CAPM framework — both plot expected return on the vertical axis and a risk measure on the horizontal axis — but they measure different things, apply to different subjects, and use different risk measures. The distinction between them is one of the most consistently tested conceptual distinctions on the Series 65 examination.

The Capital Market Line applies to efficiently diversified portfolios — those that hold the market portfolio and the risk-free asset in varying combinations — and uses total risk measured by standard deviation of portfolio returns on the horizontal axis. The CML shows the maximum expected return achievable at each level of total portfolio risk when the investor holds only efficient combinations of the market portfolio and the risk-free asset. Every point on the CML is a different allocation between the risk-free asset and the market portfolio — moving up and to the right means taking on more total risk in exchange for higher expected return.

The Security Market Line applies to individual securities and portfolios of any composition — efficient or not — and uses systematic risk measured by beta on the horizontal axis. The SML shows the required expected return for any security at each level of systematic risk, whether that security is efficiently diversified or not. Every asset — regardless of how much unsystematic risk it carries — falls somewhere on the SML if it is correctly priced, because systematic risk is the only dimension of risk that the CAPM rewards.

The practical consequence of this distinction is that the CML is used to evaluate the performance of portfolios that are meant to be efficiently diversified — comparing total risk to expected return to assess whether the portfolio is lying on the efficient frontier. The SML is used to evaluate individual securities and actively managed portfolios — comparing systematic risk to expected return to assess whether the portfolio is generating alpha above the benchmark required return for its beta level.

Shifts in the SML — Changing Market Conditions

The position and slope of the Security Market Line are not static — they shift as market conditions change, particularly as the risk-free rate and the equity risk premium fluctuate.

When the risk-free rate rises — as occurs during Federal Reserve tightening cycles — the entire SML shifts upward in parallel. Every beta level now requires a higher expected return because the risk-free component of the required return has increased. This upward shift in required returns reduces the present value of all future cash flows and produces lower prices for securities whose expected cash flows are unchanged — which is the mechanism through which Federal Reserve rate hikes transmit into lower asset valuations across all risk levels simultaneously.

When the equity risk premium rises — as occurs during periods of heightened market uncertainty, financial stress, or economic recession — the SML rotates upward, becoming steeper. The y-intercept — the risk-free rate — remains anchored, but the slope increases, meaning that high-beta securities now require meaningfully higher expected returns while low-beta securities require modestly higher returns. This steepening of the SML during risk-off periods explains why high-beta growth stocks suffer disproportionately during market stress episodes — they require the largest upward adjustment in required returns, producing the largest downward adjustment in prices.

Practical Application — Cost of Equity in Corporate Finance

Beyond its role as an investment evaluation tool, the Security Market Line's CAPM equation is the most widely used methodology for estimating the cost of equity in corporate finance — the minimum return that equity investors require from a company, which serves as the equity component of the weighted average cost of capital used in discounted cash flow valuation models.

An investment analyst valuing a publicly traded company estimates the company's beta from its historical stock price relationship to the market index — typically using sixty months of monthly return data regressed against the S&P 500 or a comparable benchmark — combines that beta estimate with the current risk-free rate and an estimate of the equity risk premium to produce the required expected return from the SML equation, and uses that required return as the cost of equity in the WACC calculation. The quality and precision of the equity valuation produced by a DCF model depends critically on the accuracy of the cost of equity estimate derived from the SML — which in turn depends on the accuracy of the beta estimate and the equity risk premium assumption.

Under the fiduciary standard of the Investment Advisers Act of 1940 and the care obligation of Regulation Best Interest at 17 CFR 240.15l-1, investment advisers using CAPM-based valuation approaches in making or evaluating securities recommendations must understand the assumptions and limitations of the model — including the sensitivity of valuations to changes in the risk-free rate and equity risk premium inputs, the instability of historical beta estimates as predictors of future systematic risk, and the possibility that the true required return for a security differs from the CAPM prediction due to additional risk factors not captured by beta alone.

Limitations of the Security Market Line

The Security Market Line is a theoretical construct that rests on assumptions that hold imperfectly in practice — and understanding its limitations is as important as understanding its application.

The CAPM assumes a single systematic risk factor — the market portfolio — but academic research beginning with Fama and French's 1992 and 1993 papers in The Journal of Finance demonstrated that multiple factors systematically explain cross-sectional variation in expected returns that the single-beta CAPM cannot account for. Size — the premium for small-cap stocks over large-cap stocks — and value — the premium for low price-to-book stocks over high price-to-book stocks — are the two additional factors Fama and French identified as systematic risk premia that the SML's single beta dimension does not capture. The subsequent development of five-factor models, momentum-augmented models, and factor-based pricing frameworks represents the continuing academic effort to build a more complete model of the security market line than the single-beta CAPM provides.

Beta instability — the empirical finding that a security's historical beta is an imperfect predictor of its future beta — reduces the SML's practical precision. Companies change their business mix, capital structure, and competitive dynamics over time in ways that alter their systematic risk exposure. Using historical beta to estimate required return over future investment horizons introduces estimation error that becomes a meaningful source of uncertainty in valuation models.

Solving the SML Equation for Its Market-Wide Inputs

The CAPM equation that the Security Market Line plots contains four quantities — the required return, the risk-free rate, beta, and the equity risk premium — and any one of the four can be recovered from the other three. Where an analyst knows a security's expected return and its beta and is willing to treat the security as correctly priced, the equity risk premium implied by that pricing is the expected return minus the risk-free rate, divided by beta. A security expected to return eleven point five percent at a beta of one point two five, in a market where the risk-free rate is three point five percent, implies a premium of eleven point five minus three point five — eight percent — divided by one point two five, which is six point four percent. The calculation inverts the equation rather than applying it: instead of taking the market's premium as given and producing a required return, it takes the security's pricing as given and produces the premium the market must be using.

Two securities that are both correctly priced fix the slope of the line between them, because two points determine a straight line. If one security has a beta of zero point eight and an expected return of eight point eight percent and another has a beta of one point six and an expected return of fourteen percent, the slope is the difference in their expected returns divided by the difference in their betas — fourteen minus eight point eight, which is five point two percentage points, divided by one point six minus zero point eight, which is zero point eight — giving six point five percent per unit of beta. That figure is the equity risk premium the two securities are jointly priced on, and it is obtained without observing the expected return on the market portfolio at all.

The same two securities also fix the intercept, which is the risk-free rate the pricing implies. Extending the line back to a beta of zero means subtracting from either security's expected return the part of it that beta accounts for: the first security gives eight point eight percent minus zero point eight multiplied by six point five, which is eight point eight minus five point two, or three point six percent, and the second gives fourteen percent minus one point six multiplied by six point five, which is fourteen minus ten point four, or three point six percent again. The two securities agree, as they must if both lie on one line, and an analyst who finds that they disagree has learned that at least one of the two is not correctly priced or that one of the two betas is wrong.

Betas At and Below Zero — The Left End of the Line

Because the line continues to the left of its intercept, a security with a negative beta has a required return BELOW the risk-free rate. With a risk-free rate of four percent and an equity risk premium of six percent, a security with a beta of negative zero point five requires four percent plus negative zero point five multiplied by six percent — four minus three, or one percent. The result is not an anomaly in the arithmetic but the economic content of the model: a security that moves against the market reduces the systematic risk of a portfolio that holds it, and investors will therefore accept a return below the certain return for the privilege of holding it.

A negative-beta security can be undervalued while offering no premium at all over the risk-free asset. A security with a beta of negative zero point four requires four percent plus negative zero point four multiplied by six percent, which is one point six percent; if it is expected to return four percent, it plots two point four percentage points above the line and is undervalued on the model's own test, even though its expected return is no better than the return available with certainty. The test is always the security's expected return against the requirement at its own beta, never its expected return against the risk-free rate.

Where a Portfolio Plots on the Line

A portfolio's required return can be computed in either of two ways, and the line's straightness is what makes the two agree. A portfolio's return is the weighted average of its holdings' returns, so its sensitivity to market movements is the weighted average of theirs. Take a portfolio with sixty percent of its value in a security with a beta of one point five and forty percent in a security with a beta of zero point five, a risk-free rate of four percent and a premium of six percent. Working from the holdings, the first security requires four plus one point five multiplied by six, or thirteen percent, the second requires four plus zero point five multiplied by six, or seven percent, and sixty percent of thirteen plus forty percent of seven is seven point eight plus two point eight — ten point six percent. Working from the portfolio, its beta is sixty percent of one point five plus forty percent of zero point five, which is zero point nine plus zero point two, or one point one, and four plus one point one multiplied by six is ten point six percent. The two routes give the same figure.

It follows that a portfolio assembled entirely from correctly priced securities is itself correctly priced and lies on the line at its own weighted-average beta. Mispricing cannot be manufactured by combination: if every holding's expected return equals the requirement at its beta, the portfolio's expected return equals the requirement at the portfolio's beta. A portfolio that plots off the line therefore contains at least one holding that plots off the line, which is why the line is applied to individual securities and portfolios in the same exercise rather than in separate ones.

A portfolio's alpha is likewise the weighted average of its holdings' alphas, so a single undervalued holding lifts the whole portfolio off the line only in proportion to its weight. A portfolio with twenty-five percent of its value in a security two percentage points above the line and seventy-five percent in securities exactly on the line has an alpha of twenty-five percent of two percentage points — zero point five of a percentage point. The arithmetic is the reason a manager with genuine insight into a small number of securities produces a modest portfolio alpha unless those positions are held in size.

How a Security Moves Onto the Line

A security that plots off the line returns to it through a change in its PRICE, which is a vertical movement on the graph, because a price change alters the expected return while leaving beta where it was. Consider a share whose expected return comes entirely from a level payment of two dollars a year. At a price of sixteen dollars it offers two divided by sixteen, or twelve point five percent; with a risk-free rate of four percent, a premium of six percent and a beta of one, the line requires four plus one multiplied by six, or ten percent, so the share plots two point five percentage points above the line. Buying pressure that lifts the price to twenty dollars brings the expected return to two divided by twenty, or ten percent, and the share now sits exactly on the line — at the same beta it always had.

A change in a security's BETA is a horizontal movement, and it can carry a correctly priced security off the line without its price having moved at all. A security with a beta of zero point nine and an expected return of nine point four percent sits exactly on a line whose intercept is four percent and whose slope is six percent, because four plus zero point nine multiplied by six is nine point four. If the company's business mix or financing changes and the beta is re-estimated at one point three, the line now requires four plus one point three multiplied by six, or eleven point eight percent, and the security plots two point four percentage points below the line on an unchanged expected return. Nothing about the security's cash flows has to change for it to become overvalued on the model's test.

Because the correction happens in the price, the return an investor earns from an above-the-line security arrives as a one-off gain rather than as a permanently higher return. In the example above, the holder who bought at sixteen dollars and saw the price reach twenty collected four dollars on sixteen — a twenty-five percent gain — once; from twenty dollars onward the share offers ten percent a year, which is exactly what the line requires of it and no more. The implication for an active manager is that alpha is harvested by being early and is extinguished by the very buying that realises it.

Reading Two Securities Against the Line

A security with the LOWER expected return of two can be the undervalued one, because each security is judged against the requirement at its own beta and not against the other security. On a risk-free rate of four percent and a premium of six percent, a security with a beta of zero point two requires five point two percent, so one expected to return six percent plots zero point eight of a percentage point above the line; a security with a beta of two point zero requires sixteen percent, so one expected to return fourteen percent plots two percentage points below it. The six percent security is undervalued and the fourteen percent security is overvalued, which is the whole point of plotting return against systematic risk rather than ranking securities by return.

Two securities with the SAME expected return and different betas cannot both lie on the line, and the higher-beta one is the one below it. If both are expected to return nine percent, on the same four percent risk-free rate and six percent premium, the security with a beta of zero point six requires seven point six percent and plots one point four percentage points above the line, while the security with a beta of one point four requires twelve point four percent and plots three point four percentage points below it. An equal expected return is not equal value, because the two securities are being paid the same for unequal amounts of systematic risk.

An analyst who finds that every security in a group plots on the same side of the line has more reason to re-examine the two market-wide inputs than to conclude that the whole group is mispriced. The required return of every security in the group is computed from the same risk-free rate and the same estimate of the equity risk premium, so an error in either of those two figures displaces every security in the same direction at once, whereas a genuine mispricing is a statement about one security's own expected return. A finding that moves with an input shared by every security in the sample is weak evidence about any individual security in it.

What Moves the Line Itself

Where the risk-free rate rises and the EXPECTED MARKET RETURN is unchanged, the premium falls by the amount the rate rose, because the premium is the expected market return minus the risk-free rate. The line's intercept rises and its slope falls, so it becomes flatter rather than shifting in parallel, and it pivots at a beta of one. On a risk-free rate going from three percent to five percent with an expected market return held at ten percent, the premium falls from seven percent to five percent: a beta of zero point five goes from six point five percent to seven point five percent, a beta of one stays at ten percent, and a beta of two falls from seventeen percent to fifteen percent. Whether a rate rise lifts the whole line or tilts it therefore depends entirely on which of the two market figures — the premium or the expected market return — is being held fixed, and an analyst must say which.

Because alpha is measured vertically from the line, a movement of the line changes every security's alpha even though no security has changed. A parallel upward shift of one percentage point reduces every security's alpha by exactly one percentage point and leaves the ranking of securities by alpha untouched; a steepening of one percentage point in the premium reduces a security's alpha by its beta — zero point five of a point for a beta of zero point five and two points for a beta of two — and so reorders them, penalising the high-beta holdings most. An alpha figure is therefore a statement about a security at a moment, measured against the line that stood at that moment.

The Two Lines Read Together

A correctly priced security that carries a large amount of diversifiable risk lies ON the Security Market Line and BELOW the Capital Market Line at the same time, and the two statements do not conflict. The Security Market Line prices beta alone, so the security's position on it is settled once its systematic risk is known; the Capital Market Line shows the maximum expected return achievable at each level of total portfolio risk for an investor who holds only the market portfolio and the risk-free asset, and the undiversified security's total risk exceeds its systematic risk. Measured against its total risk the security therefore offers less than the best available combination, which is the geometric statement of the fact that the model pays nothing for risk a portfolio could have diversified away.

Every portfolio on the Capital Market Line also lies on the Security Market Line, because a combination of the market portfolio and the risk-free asset has a beta equal to its weight in the market portfolio. A portfolio sixty percent in the market portfolio and forty percent in the risk-free asset has a beta of sixty percent of one plus forty percent of zero, which is zero point six. Its expected return is forty percent of the risk-free rate plus sixty percent of the expected market return — with a risk-free rate of four percent and an expected market return of ten percent, that is one point six plus six, or seven point six percent. The Security Market Line requires four plus zero point six multiplied by six, which is seven point six percent as well. The lines describe the same securities in different co-ordinates, and they disagree only about securities and portfolios that the Capital Market Line does not describe.

Plotting a security's standard deviation on the Security Market Line's horizontal axis is an error that changes the answer, because the line's requirement is a function of beta and of nothing else. A security whose returns swing violently for reasons unconnected to the market has a low beta, and on a risk-free rate of four percent and a premium of six percent a beta of zero point three requires five point eight percent however large that security's total volatility is. Read on the correct axis the security is expensive at anything less than five point eight percent; read on the wrong axis it would appear to require a great deal more, and a correctly priced security would be rejected as overvalued.

Common Errors in Applying the Line

An error in the beta estimate passes straight into the alpha, because alpha is the gap between the expected return and a requirement computed from that beta. With a risk-free rate of four percent and a premium of six percent, a security whose beta is taken as one requires ten percent, and one expected to return eleven percent shows a full point of alpha; if the beta is in fact one point two the requirement is eleven point two percent and the same security shows an alpha of negative zero point two. A beta understated by zero point two overstates the alpha by zero point two multiplied by the premium — one point two percentage points — so an apparent alpha of about a point says as much about the regression that produced the beta as about the security.

Two analysts can place the same security on opposite sides of the line without disagreeing about the line at all, because the required return is built from market-wide figures while the expected return is each analyst's own forecast. On a risk-free rate of four percent and a premium of six percent, a security with a beta of one point five requires thirteen percent; an analyst expecting fourteen percent from it reads an alpha of one point and an analyst expecting twelve percent reads an alpha of negative one point. The line settles what the security must return; it settles nothing about what the security will return, and the disagreement that active management consists of lives entirely on the other side of the comparison.

The two sides of the comparison are also measured over different periods, which is a limitation of the test rather than a defect in the arithmetic. The expected return is a forward-looking estimate of what the security will do, while the beta that sets the requirement is estimated by regressing sixty months of past monthly returns against an index. The position a security takes relative to the line thus combines a forecast about the future with a measurement of the past, and the comparison is only as good as the assumption that the systematic risk measured over those past months is the systematic risk the security will carry over the period being forecast.

The Line Inside a Cost-of-Equity Estimate

The sensitivity of a cost-of-equity estimate to the premium assumption is scaled by beta, so the same disagreement about the premium matters more for some companies than for others. Because the required return is the risk-free rate plus beta multiplied by the premium, raising the premium assumption from five percent to six percent raises the cost of equity of a company with a beta of one point six, at a risk-free rate of four percent, from twelve percent to thirteen point six percent — one point six points — and that of a company with a beta of zero point six from seven percent to seven point six percent, which is zero point six of a point. A valuation of a high-beta company therefore carries more of the analyst's premium assumption in it than a valuation of a low-beta company does, and the sensitivity analysis should be sized accordingly.

A cost of equity arrived at by adding a company-specific premium to the figure the line produces is no longer the CAPM required return, and an analyst who does it should say so. The equation prices beta and nothing else, so any addition on top of it is compensation for something the model does not price — which is a coherent response to the model's own limitation, since the true required return for a security can differ from the CAPM prediction because of risk factors beta does not capture, but it is a departure from the line rather than an application of it. Describing the result as the CAPM cost of equity conceals the size of the addition, which is usually the most contestable number in the estimate.

Examination Relevance and Key Takeaways

The Security Market Line is tested on the Series 65 examination in the context of the CAPM, systematic risk, beta, alpha, the distinction from the Capital Market Line, and the identification of undervalued and overvalued securities relative to their risk-adjusted required returns.

The key points to retain are these.

The Security Market Line is the graphical representation of the CAPM equation — plotting beta on the horizontal axis and expected return on the vertical axis as a straight line. The y-intercept equals the risk-free rate — the required return when beta equals zero. The slope equals the equity risk premium — the expected market return minus the risk-free rate — which is the additional return per unit of beta required by the market as compensation for systematic risk. The CAPM equation states that expected return equals the risk-free rate plus beta multiplied by the equity risk premium. Every correctly priced security in the CAPM framework lies exactly on the SML.

Securities above the SML are undervalued — they offer more return than their systematic risk requires — attracting buying that drives prices up until expected returns fall back to the line. Securities below the SML are overvalued — they offer less return than their systematic risk requires — attracting selling that drives prices down until expected returns rise back to the line. Alpha is the vertical distance from the SML — positive alpha indicates above-SML positioning and excess return above the risk-adjusted benchmark; negative alpha indicates below-SML positioning and return shortfall relative to the risk-adjusted benchmark. 

The SML applies to individual securities and all portfolios using systematic risk — beta — as the risk measure. The Capital Market Line applies only to efficiently diversified portfolios — those combining the market portfolio and the risk-free asset — using total risk measured by standard deviation as the risk measure. Rising risk-free rates shift the entire SML upward in parallel. Rising equity risk premiums rotate the SML upward, steepening it most severely for high-beta securities.