Updated for the 2026-2027 CFA® Level I curriculum.
Beta measures how sensitive an asset's returns are to movements in the overall market. It is one of the most tested numbers in Portfolio Management because it links directly to CAPM, systematic risk, and portfolio construction questions. Level I exams ask you to calculate beta from covariance and variance, read it off a regression output, and combine individual betas into a portfolio beta.
Quick Answer
Beta measures an asset's sensitivity to market returns. The formula is:
where is the covariance between the asset's returns and the market's returns, and is the variance of market returns. Beta is also the slope coefficient from a regression of asset returns on market returns.
Portfolio beta is the weighted average of the betas of the assets it holds: . A beta above 1 means the asset moves more than the market. A beta below 1 means it moves less.
Key Takeaways About Beta: Calculation and Interpretation
Beta is a measure of systematic risk, the risk that cannot be diversified away.
The formula always uses market variance in the denominator, not asset variance.
Beta equals the slope of the regression line when asset returns are regressed on market returns.
Portfolio beta is a weighted average of individual asset betas, using portfolio weights.
Beta can be negative, zero, or greater than one. Each case has a distinct meaning for how the asset moves relative to the market.
Beta measures relative volatility to the market. It does not measure total risk or correlation directly.
What You Need to Know for CFA Level I
Recognize beta as a measure of an asset's sensitivity to market returns, not its total risk.
Apply the formula correctly, using market variance in the denominator.
Identify beta as the slope coefficient in a single-variable regression of asset returns on market returns.
Calculate portfolio beta as the weighted average of individual security betas.
Interpret beta values above, below, equal to, and less than zero, including negative beta.
Avoid confusing beta with correlation or with standard deviation.
Beta as Sensitivity to Market Returns
Beta answers one question: when the market moves 1%, how much does this asset typically move? An asset with a beta of 1.3 tends to move 1.3% for every 1% move in the market, in the same direction. An asset with a beta of 0.6 tends to move only 0.6% for the same market move.
This makes beta a measure of systematic risk, the portion of an asset's risk tied to broad market movements. Systematic risk cannot be eliminated through diversification, which is why CAPM uses beta, not total variance, to price expected return. Level I questions test this distinction directly. Beta captures market-related risk. It says nothing about company-specific risk, which diversification does remove.
The Covariance-Over-Market-Variance Formula
The formal definition of beta is:
Notation legend:
= beta of asset
= covariance between asset 's returns and market returns
= variance of market returns
Both covariance and variance are typically calculated from historical return series, expressed in decimal or percentage terms. Beta itself is unitless. It is a ratio, so the units cancel.
The key exam trap sits in the denominator. Candidates sometimes plug in the asset's own variance instead of the market's variance. The formula only works with market variance in the denominator, because beta measures the asset's movement relative to the market, not the asset's risk in isolation.
Regression Slope Interpretation
Beta can also be estimated using linear regression. If you regress an asset's historical returns (the dependent variable) against market returns (the independent variable), the slope coefficient of that regression line is beta.
This connects beta to a familiar quantitative concept: the regression equation . Here, is the intercept, captures the market-driven portion of returns, and is the residual, or asset-specific, return not explained by the market. On the exam, if you see a regression output with an asset's returns regressed on market returns, the coefficient on the market return variable is beta. No further calculation is needed.
Portfolio Beta
A portfolio's beta is the weighted average of the betas of the individual holdings, using the market value weight of each position:
Notation legend:
= beta of the portfolio
= weight of asset in the portfolio, based on market value
= beta of asset
This formula treats portfolio beta as a straightforward weighted sum. There is no adjustment for correlation between assets in this calculation, because each individual beta already reflects each asset's relationship to the same market benchmark.
Beta Value | Interpretation |
|---|---|
Negative | Asset tends to move opposite the market. Rare, but possible for assets like some hedges or short positions. |
Zero | Asset returns show no systematic relationship with market returns. |
Between 0 and 1 | Asset moves in the same direction as the market, but with less magnitude. Lower systematic risk than the market. |
Equal to 1 | Asset moves in line with the market, on average. Systematic risk matches the market. |
Greater than 1 | Asset moves in the same direction as the market, but with more magnitude. Higher systematic risk than the market. |
Worked Example
Scenario: An analyst is reviewing a three-stock portfolio held by a client.
Step 1: Calculate an individual asset beta
The analyst has historical return data for Stock A and the market index:
Stock A has a beta of 1.20. It tends to move 20% more than the market in either direction.
Step 2: Calculate portfolio beta
The portfolio holds three stocks with the following weights and betas:
Stock | Weight | Beta |
|---|---|---|
A | 40% | 1.20 |
B | 35% | 0.80 |
C | 25% | 1.50 |
This portfolio has a beta of 1.135. For every 1% move in the market, the portfolio is expected to move about 1.135% in the same direction. The portfolio carries slightly more systematic risk than the overall market.
If the client wants to reduce market sensitivity, the analyst would need to shift weight toward Stock B, the lowest-beta holding, or add a low-beta or negative-beta asset.
Common Exam Traps
Using asset variance in the denominator
The beta formula divides by market variance, not the asset's own variance. Swapping these produces a completely different, incorrect number.
Treating beta as total risk
Beta only captures systematic risk. An asset can have low beta and still carry significant company-specific risk that beta does not reflect.
Assuming beta cannot be negative
Most exam questions use positive betas, but a negative beta is mathematically valid. It means the asset tends to move opposite the market.
Confusing beta with correlation
Correlation measures the strength and direction of a linear relationship, bounded between -1 and 1. Beta measures sensitivity and scales with relative volatility, so it can exceed 1 or fall below -1.
Practice Questions
An analyst builds a portfolio with three funds:
Fund | Weight | Beta |
|---|---|---|
X | 50% | 0.90 |
Y | 30% | 1.40 |
Z | 20% | -0.20 |
What is the portfolio's beta?
0.83
0.91
0.70
Correct Answer: A. 0.83
Explanation: Portfolio beta is the weighted average of individual betas.
Option B: This results from treating Fund Z's beta as positive 0.20 instead of negative 0.20, producing 0.45 + 0.42 + 0.04 = 0.91.
Option C: This results from taking a simple average of the three betas , ignoring portfolio weights entirely.
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FAQs About Beta: Calculation and Interpretation
Is a higher beta always riskier?
A higher beta means more sensitivity to market movements, not more total risk. An asset can have a high beta but low total risk if its company-specific risk is minimal.
How is beta calculated in CFA Level I problems?
Most Level I questions give you covariance and variance directly, or a regression output. You apply or read the slope coefficient from the regression.
What does a beta of 1 mean for a stock?
A beta of 1 means the stock's returns tend to move in line with the market, both in direction and magnitude, on average.