Alpha
The excess return of an investment relative to a benchmark, after adjusting for the level of market risk taken.
What is Alpha?
Alpha (α) measures the value added by an investment manager or strategy beyond what would be expected given its level of market risk (beta). A positive alpha means the investment outperformed its benchmark on a risk-adjusted basis; a negative alpha means it underperformed. In the Capital Asset Pricing Model (CAPM), alpha is the y-intercept of the security's characteristic line: Alpha = Actual Return − (Risk-Free Rate + Beta × (Market Return − Risk-Free Rate)). For example, if a fund returned 12% when CAPM predicted 9% based on its beta and market return, its alpha is 3%. In practice, generating consistent positive alpha after fees is extremely difficult; studies show most actively managed funds have negative alpha net of fees over time.
Example
Hedge fund manager Jim Simons' Medallion Fund generated an average gross return of approximately 66% per year from 1988 to 2018, far exceeding any reasonable benchmark expectation — among the highest documented alpha in investment history. The fund's alpha was so large and consistent that it remains a subject of academic study, with most researchers attributing it to proprietary quantitative strategies exploiting systematic market inefficiencies.