Alpha
Explanation
Alpha represents the portion of a portfolio's return that cannot be explained by exposure to market risk. A portfolio with an alpha of 2% earned 2 percentage points more than what the Capital Asset Pricing Model predicted based on its beta.
Alpha is the most widely cited measure of active management skill. Positive alpha indicates the manager (or algorithm) added value beyond passive market exposure. Negative alpha means the strategy underperformed what a simple index fund would have delivered at the same risk level.
In practical terms, generating consistent alpha is difficult. The S&P Dow Jones SPIVA scorecard shows that over 15-year periods, roughly 90% of actively managed large-cap funds fail to beat the S&P 500. This is why alpha—even small, consistent amounts—is considered valuable.
Formula
| Variable | Meaning |
|---|---|
| α | Alpha (excess return) |
| Rp | Portfolio return |
| Rf | Risk-free rate (e.g., 3-month T-bill) |
| β | Portfolio beta (systematic risk) |
| Rm | Market return (e.g., S&P 500) |
Example
A portfolio returned 14% over the past year. The risk-free rate was 5%, the S&P 500 returned 11%, and the portfolio's beta is 1.1.
The portfolio earned 2.4% more than what its market risk exposure alone would predict. This positive alpha suggests genuine stock-selection skill rather than simply riding market momentum.
How Stoquity Uses This
Stoquity calculates rolling alpha for each portfolio on the Analytics tab. The AI engine targets positive alpha by combining 24 factor scores with committee-vetted trade signals. Each portfolio's alpha is measured against the S&P 500, with daily updates visible to all plan tiers.
Common Mistakes
- Confusing alpha with total return—a fund can have high returns but negative alpha if it took excessive risk
- Assuming alpha is persistent—past alpha does not guarantee future alpha
- Ignoring the benchmark—alpha is meaningless without specifying which index you are comparing against