What Is Active Share?
Active share measures how much a fund’s holdings differ from its benchmark index, expressed as a percentage. The concept was introduced by professors Martijn Cremers and Antti Petajisto in 2009 and is used to gauge how genuinely ‘active’ a portfolio manager’s stock selection really is.
The Active Share Formula
Active share is calculated as: Sum of the absolute differences between each holding’s weight in the fund and its weight in the benchmark, divided by two. If Fund D has an active share of 72%, it means 72% of the portfolio’s weight reflects genuinely independent stock selection that departs from the benchmark composition.
Identifying Closet Indexing
When a fund’s active share falls below roughly 60% while it still charges fees typical of active management, it raises the possibility of ‘closet indexing’ — effectively hugging the benchmark while marketed as an actively managed strategy. Investors in such funds risk paying active fees for what amounts to index-like performance.
Using Active Share to Judge Fund Fees
A higher active share (commonly above 60–80%) suggests more of the fund’s performance depends on the manager’s individual stock-picking skill, which some investors see as justifying a higher fee. Conversely, a low active share weakens the case for paying active-management fees rather than switching to a lower-cost index fund or ETF.
Active Share and Tracking Error Together
Active share measures how different the holdings are, while tracking error measures how different the returns are. A fund with high active share but low tracking error may hold different individual stocks while still maintaining similar sector or factor exposure to its benchmark overall.
| Fund Type | Active Share | Characteristic |
|---|---|---|
| Closet Indexer | 35% | Near-benchmark holdings, active fees |
| Fund D | 72% | Genuinely differentiated stock selection |
| High-Conviction Active | 90% | Portfolio largely independent of benchmark |
Frequently Asked Questions
Does high active share guarantee good performance?
No — active share measures how different a portfolio is from its benchmark, not whether those differences pay off. Poor stock selection with high active share can underperform the benchmark just as easily as good selection can outperform it.
Where can I find a fund’s active share?
Some asset managers disclose active share in fund fact sheets, and independent fund research platforms sometimes report it as part of their evaluation coverage.
How is active share different from beta?
Beta measures a fund’s price sensitivity relative to the market, while active share measures how different the portfolio’s actual holdings are from the benchmark’s — they capture distinct dimensions of a fund’s positioning.
How can I avoid closet indexers?
Checking a fund’s active share before investing, and asking the manager to explain the specific sources of expected outperformance (alpha), can help identify funds that are genuinely active rather than benchmark-hugging.
Key Takeaways
Active share measures how much a fund’s holdings diverge from its benchmark, and a reading below 60% is a signal to check for closet indexing. Reviewed alongside tracking error, it helps investors judge whether an active fund’s fees are justified by genuinely differentiated stock selection. This article is for informational purposes only and does not constitute investment advice.
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