Mutual Fund Portfolio Overlap: The 50% Rule Explained

When investors build a mutual fund portfolio, a common but often overlooked problem is portfolio overlap. This happens when multiple funds you hold invest in largely the same set of stocks or securities. The result is that your capital, spread across several fund names, is not truly diversified. You may feel protected by holding more funds, but if those funds mirror each other's holdings, the diversification is largely cosmetic.

Understanding portfolio overlap — and the regulatory framework now being applied to contain it — is essential for anyone who wants their money to work across genuinely different market opportunities.

What Is Mutual Fund Portfolio Overlap?

Mutual fund portfolio overlap refers to the degree to which two or more funds in your investment basket share common underlying holdings. If two large-cap equity funds both hold the same dominant stocks in similar proportions, owning both adds little real diversification to your portfolio. In practice, the combined effect on your overall returns and risk exposure will behave much like holding a single, larger position in just one of those funds.

Overlap is not inherently wrong in small doses. Some convergence in holdings among funds in the same category is natural. The problem arises when the overlap is so significant that it renders one of the funds redundant from a portfolio construction perspective.

Why Portfolio Overlap Is a Problem for Investors

The core purpose of investing across multiple mutual fund schemes is to spread risk and capture returns from different market segments, sectors, or investment styles. Excessive overlap undermines this goal in several ways.

First, it creates a false sense of diversification. An investor holding three funds with heavily overlapping portfolios may believe their risk is spread across three independent bets, when in reality the exposure is concentrated in the same underlying securities.

Second, it increases costs without proportionate benefit. Each fund carries its own expense ratio and transaction costs. When two funds behave nearly identically, the investor effectively pays twice for the same outcome.

Third, it makes portfolio review more complicated. Tracking the true composition of your investments becomes harder when overlapping funds blur the lines between your actual holdings.

What Is Closet Indexing?

Closet indexing is a specific form of overlap-related concern at the fund level rather than the investor level. A closet indexer is an actively managed fund that, despite claiming to deliver active management, closely mirrors the composition and performance of a benchmark index. The fund charges fees associated with active management while essentially delivering index-like results.

SEBI has been alert to this practice for several years. The concern is that investors pay a premium for active stock selection that is not actually occurring to any meaningful degree. From a regulatory standpoint, closet indexing is seen as a form of misrepresentation — not in an outright fraudulent sense, but in the sense that the fund's positioning does not match what investors reasonably expect.

The 50% Rule and What It Means

Regulatory thinking around portfolio overlap has evolved significantly leading into 2026. The central idea behind what is commonly referred to as the 50% rule is straightforward: if a proposed new fund scheme from an asset management company shares more than a defined threshold of its portfolio overlap with an existing scheme from the same AMC, it should not be launched as a separate product.

The logic is protective in two directions. It protects investors from buying into a scheme that offers no genuine differentiation from something they may already hold. It also prevents AMCs from proliferating schemes that serve commercial interests — asset gathering — rather than investor interests.

By setting an overlap threshold at or around the midpoint of possible holdings convergence, the rule creates a clear and measurable standard. Any scheme that a fund house wishes to introduce must be demonstrably different from its existing lineup in terms of the securities it holds, the sectors it targets, or the investment strategy it employs. Overlap beyond that threshold disqualifies the new scheme from launch.

How the 2026 Rules Prevent Redundant Fund Schemes

Before this regulatory tightening, the Indian mutual fund industry had seen a steady proliferation of schemes. Many of these were thematically similar — funds built around narratives like digital economy, domestic consumption, or infrastructure — but with holdings that were substantially identical across different AMCs or even within the same AMC's product range.

The 2026 rules address this at the source. Now, before an AMC can register and launch a new scheme, it must demonstrate to regulators that the new offering is sufficiently distinct from its existing schemes. The assessment looks at the actual stock-level or security-level composition, not merely the marketing label or thematic name.

This has several practical effects. Fund houses are now incentivised to develop genuinely differentiated investment strategies rather than rebranding similar portfolios. The overall number of available schemes is expected to be more curated. Investors benefit because each scheme on the market is, in principle, offering something meaningfully different.

For the investor, this means that when you compare two schemes — even from the same broad category — you can have greater confidence that they represent distinct investment philosophies and hold different underlying assets.

How to Check and Manage Overlap in Your Own Portfolio

Even with regulatory safeguards at the AMC level, individual investor portfolios can still accumulate overlap over time, particularly if you have added funds from different houses that happen to invest in similar securities.

The most straightforward way to manage this is to periodically review the top holdings of each fund you own and compare them. If you find that the same companies appear prominently across most of your funds, you are likely experiencing meaningful overlap. In such cases, consolidating to fewer, more strategically distinct funds is usually the wiser approach.

A general principle worth keeping in mind: more funds do not automatically mean more diversification. A well-constructed portfolio of a smaller number of clearly differentiated funds will almost always serve you better than a large collection of schemes with overlapping mandates.

Platforms like Stashfin are designed to help investors navigate these decisions with clarity. When you Explore Mutual Funds on Stashfin, you can assess fund options with the goal of building a portfolio that is genuinely diversified — not just diversified by name.

The Broader Significance for the Mutual Fund Industry

The regulatory direction on portfolio overlap reflects a broader maturation of the Indian mutual fund regulatory framework. SEBI and AMFI have, over the years, moved toward greater transparency, standardisation of scheme categories, and investor-first rule-making. The 50% overlap rule sits within this continuum.

For investors, the takeaway is that the regulatory environment is actively working to reduce information asymmetry and protect against practices — like closet indexing and scheme proliferation — that benefit fund houses more than the people who invest their savings.

This does not mean investors can be passive. Understanding the concept of portfolio overlap, knowing how to evaluate your own holdings, and staying informed about regulatory developments all remain important responsibilities for anyone participating in the mutual fund market.

Mutual fund investments are subject to market risks. Past performance is not an indicator of future returns. Please read all scheme-related documents carefully before investing.