What Is 'Active Share' and How Does It Help Compare Actively Managed Funds?
Two funds can both claim to be “actively managed” and charge similar fees, yet hold portfolios that look nearly identical to the index they’re supposedly trying to beat. A statistic called active share was built to expose exactly that gap, and it rarely shows up in a fund’s own marketing materials.
The short answer
Active share measures how much a fund’s holdings differ from its benchmark index, expressed as a percentage from 0 to 100. A fund with a high active share holds a portfolio that looks quite different from its benchmark, while a fund with a low active share largely mirrors the index it’s compared against, even if it’s marketed and priced as an active strategy.
How the number is built
Active share is calculated by comparing the weight of each holding in a fund to the weight of that same holding in its benchmark, adding up the differences, and dividing by two. A fund that held every stock in its benchmark at the same weight would have an active share near zero. A fund with no overlap in holdings at all would approach 100. As a simplified illustration, a fund holding half its assets in stocks entirely absent from its benchmark, and the other half at the same weights as the benchmark, would land at an active share of roughly 50. Most actively managed funds land somewhere in between, and where they land says something about how differently the fund manager is actually behaving from the index.
Why a low number raises questions
A fund charging active-management-level fees while carrying a low active share is sometimes described informally as “closet indexing” — holding a portfolio close enough to its benchmark that it’s unlikely to meaningfully outperform or underperform, but still charging for the decision-making of a hands-on approach. Comparing the expense ratio a fund charges against its active share can highlight whether a fund’s price tag matches how much independent decision-making it’s actually doing. This gap between cost and behavior is one reason active share became popular as a due-diligence check rather than a marketing statistic, since it doesn’t depend on how a fund chooses to describe itself.
What a high number does and doesn’t promise
A high active share means a fund looks different from its benchmark, not that those differences will pay off. A manager who deviates heavily from an index can be right or wrong, and a high active share cuts both ways — it raises the potential for outperformance and underperformance alike. It’s a measure of divergence, not a measure of skill or of future results. It also says nothing about how concentrated or diversified those different holdings are, which is worth checking separately before drawing broader conclusions.
Using it alongside other comparisons
Active share works best paired with other numbers rather than read alone. A statistic like R-squared shows how much of a fund’s movement is explained by its benchmark in the first place, which helps confirm whether the benchmark being used for the active share comparison is even a sensible one. Looking at a fund’s turnover ratio alongside its active share can also clarify whether a fund arrived at its distinctive portfolio through patient, long-held convictions or through frequent trading. And comparing active share against a plain index fund option can put the question in perspective: is the fund different enough from a low-cost index alternative to justify its own approach and pricing?
The bottom line
Active share is a way of checking whether an actively managed fund is actually acting active, rather than assuming the label on the fund tells the whole story. On its own it doesn’t say whether a fund’s approach paid off, but combined with cost and other comparison tools, it gives a clearer picture of what an investor is actually paying for.