Benchmark index

A benchmark index is a market index, such as a broad stock or bond index, chosen as the reference point against which a portfolio's or fund's return and risk are measured. Choosing an appropriate benchmark is a core part of evaluating whether a manager added value, since a fund can look strong or weak depending entirely on what it is compared against.

A benchmark should match the portfolio's investment universe and style — for example, a small-cap value fund is properly compared to a small-cap value index rather than a broad large-cap index, otherwise measures like tracking error and relative return become misleading. Outperformance versus the benchmark, adjusted for risk, is often summarized as alpha, while the benchmark's own volatility and correlation underpin a portfolio's beta.

Benchmarks are used throughout investing: to set fund objectives, to structure passive index funds designed to replicate the benchmark at a low expense ratio, and to judge active managers against a passive alternative. A common pitfall is benchmark misfit, comparing a fund to an index that does not reflect its actual holdings or strategy, which can make skilled managers look poor or unskilled ones look strong, and switching benchmarks after the fact to flatter results, sometimes called benchmark shopping.