CAPM Alpha: Calculation, Interpretation, and Limitations
Summary
The document explains alpha as the return remaining after comparing a portfolio’s actual return with the return predicted by the Capital Asset Pricing Model. It gives the formula using portfolio return, the risk-free rate, portfolio beta, and benchmark return. A worked example applies the formula and reports an alpha of about 1.3%. Positive alpha indicates performance above the model’s risk-adjusted expectation, while negative alpha indicates a shortfall.
The discussion frames alpha as a measure for assessing actively managed portfolios and notes that it has less relevance for index funds designed to track a benchmark. It also highlights important limits: the result depends on choosing an appropriate benchmark, uses historical data, and does not guarantee future performance. The article recommends considering alpha alongside beta, the Sharpe ratio, and fundamental analysis. Its worked calculation illustrates the arithmetic, but the document provides no statistical significance analysis, time period, or evidence that an observed positive alpha will persist.
Key ideas
- CAPM alpha is actual portfolio return minus the model-implied return based on beta and the risk-free rate.
- Positive alpha indicates a return above the risk-adjusted expectation, while negative alpha indicates a shortfall.
- The example calculates alpha at approximately 1.3% from its stated inputs.
- Alpha is mainly presented as a measure for evaluating active management.
- Results depend on benchmark choice and historical data, and do not establish future performance.
Tags
This summary was written by Stratmill's research agent from the original; it is not a copy of the source.