Alpha

Stock trading dictionary: meaning, example and how traders use it.

Last updated: October 17, 2026

Definition: Alpha is the portion of an investment's return that cannot be explained by its market exposure. A positive alpha means the investment beat the return its risk level would predict; a negative alpha means it fell short.

How alpha works

Investors rarely judge a fund or stock by raw return alone. A portfolio that rose 15% may have done well or poorly depending on how much the market rose and how much risk it took. Alpha isolates the excess: the return above a benchmark after adjusting for market sensitivity, usually measured by beta.

In simple usage, alpha is the difference between a fund's return and its benchmark index, such as the S&P 500. In the more formal version, often called Jensen's alpha, the benchmark is adjusted for beta using the capital asset pricing model.

Positive alpha is what active managers aim to deliver, and it is the reason investors pay higher fees for active funds than for passive ones. Measuring it honestly requires a benchmark that matches the fund's style, size, and region; otherwise apparent skill may simply reflect exposure to a segment of the market that happened to do well.

Alpha formula

Jensen's alpha is calculated as:

Alpha = Actual return - [Risk-free rate + Beta x (Market return - Risk-free rate)]

The bracketed term is the expected return given the investment's market risk. Anything above it is alpha.

Example: calculating alpha

Suppose a hypothetical fund returned 12% over a year. The market index returned 10%, the risk-free rate (for example, a short-term Treasury yield) was 3%, and the fund's beta is 1.2.

  1. Market excess return: 10% - 3% = 7%.
  2. Beta-adjusted excess: 1.2 x 7% = 8.4%.
  3. Expected return: 3% + 8.4% = 11.4%.
  4. Alpha: 12% - 11.4% = 0.6%.

Although the fund beat the index by 2 percentage points, most of that came from taking more market risk. Its risk-adjusted outperformance was only 0.6 percentage points.

Alpha vs beta

Beta measures how much an investment moves with the market, while alpha measures what it earns beyond that exposure. Low-cost index ETFs aim for a beta near 1 and an alpha close to zero before fees. Active managers, by contrast, are paid to generate positive alpha through stock selection, timing, or strategies such as arbitrage.

Limitations of alpha

Alpha depends heavily on the benchmark chosen; comparing a small-cap fund to a large-cap index can create misleading results. Past alpha is often not persistent, and fees can erase it. Alpha also says nothing about other investment risks such as concentration or liquidity, so it is best read alongside volatility and drawdown measures.

Analysts sometimes annualize alpha from monthly data or estimate it with a regression of fund returns on market returns, where alpha is the intercept.

Frequently asked questions

What is a good alpha?

Any consistently positive alpha after fees is considered favorable, since it means returns exceeded what market risk alone would predict. Because alpha often fades over time, consistency matters more than a single strong year.

Can alpha be negative?

Yes. A negative alpha means the investment underperformed the return expected for its level of market risk, which is common for actively managed funds after fees.

What is the difference between alpha and beta?

Beta measures sensitivity to market moves, while alpha measures the return earned above what that sensitivity would predict.

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For information only, not investment advice. See the disclaimer.