IS Your Index Fund Really Diversified among sectors, or does it function more like Sectoral/Thematic Funds?

Synopsis

The go-to darling for retail investors is the index fund; think of an index fund as the “copycat” of the market. That is, the fund will show similar movement to the market, and these funds are a type of passive fund; that is, they tend to replicate the price movement of the market and have no objective of beating the market by returns.

Now, a Passive Investor might invest in a fund like the Nifty 50 Index fund, thinking that the fund will provide diversification across sectors, but is it so? Do these funds really provide diversification, or is your money being concentrated in a few sectors at the top? With this research, I will explore the same and take you through various findings.

Keeping things simple, we will be sticking to the Nifty 50 as our Index and the fund related to it. As mentioned earlier, Index Funds are passive funds, and their only task is to generate a return similar to the market/index it is tracking; hence, an investor who is investing in this fund might not expect a return more than the market, but rather match the market performance. An index investor should follow the tracking error of the fund, as less tracking error means the fund is highly correlated.

Now, let's explore whether or not an index fund is really diversified or if investment is mostly concentrated in a few sectors/stocks. When looking at all 50 stocks of the Nifty 50 and their cumulative weights, the top 5 stocks up till Maruti Suzuki have a cumulative weight of almost 50%; that is, every ₹100 invested in any of these funds will result in almost ₹50 being allotted in these 5 stocks and the remaining ₹50 spread across the other 45 stocks.

Coming to sector allocation, the top 5 sectors (Banking, Crude Oil, IT, Automobile & Ancillary, and Finance) account for almost 60% concentration; that is, for every ₹100 invested, ₹60 goes to these 5 sectors while the remaining is distributed across all other sectors.

Another insight is that most allocation is concentrated in sectors that have little direct incentive from AI and AI-related investments; as a result, Indian heavyweight stocks have faced headwinds during the global AI rally, contributing to Nifty's year-to-date pressure.

Sectors or stocks with heavy weights possess far greater capability of pulling the index up or down. If the top 10 heavyweight stocks fell by 5% in one day, it would pull the entire index down by over 2%, whereas a 5% drop across the bottom 10 stocks would move the index by less than 1%.

Why Has the Nifty 50 Lagged in 2026?

At first glance, one may wonder why this matters. A key reason behind the Nifty 50’s relatively weak performance in 2026 is India’s limited exposure to AI and AI-related investments. Simply expanding data-centre capacity may not be enough for the country to capture the broader benefits of the AI investment cycle. The composition of the Nifty 50 also plays an important role, as several of its heavyweight sectors have limited direct exposure to AI-driven growth.

Performance of Major Nifty Sectors in 2026

The year-to-date performance of some major sectors highlights this trend:

• Nifty Bank: -2.96%
• Oil & Gas: -7.06%
• IT: -23.60%
• Auto: -5.10%

These sectors carry significant weight in the Nifty 50 and have remained among the weaker performers so far in 2026. Their underperformance has therefore placed considerable pressure on the overall index, preventing it from benefiting fully from stronger performance in other areas.

Is Nifty 50 Really as Diversified as It Appears?

Investing in the Nifty 50 certainly provides greater diversification than investing in a single stock or a concentrated sectoral fund. However, diversification at the stock level does not necessarily mean equal exposure across the economy. The index remains significantly influenced by the sectors and companies that carry the highest weights.

This means investors may avoid the extreme drawdowns associated with highly concentrated sectoral funds, but they are still exposed to the performance of major sectors within the index. When heavyweight sectors struggle, their impact can be large enough to pull down the broader index, even when several smaller sectors perform well.

Where Does Your ₹100 Actually Go?

Another way to understand this concentration is to look at how the index allocates capital. If you invest ₹100, approximately ₹15 may be allocated to private banks, ₹9 to refineries, and the remaining amount distributed across other industries.

The important point is that a substantial portion of the investment is concentrated within the largest five industries. This creates greater sensitivity to events affecting those sectors. Factors such as geopolitical tensions, macroeconomic developments, interest-rate changes, commodity prices, and currency movements can therefore have a significant impact on the index.

Why Sector Concentration Matters

The Nifty 50’s performance in 2026 illustrates this clearly. The index has delivered approximately -8% to -9% YTD, despite stronger performance from sectors such as FMCG and healthcare. Weakness in major areas such as banking, oil, and IT has outweighed gains elsewhere.

Several factors have contributed to this pressure, including the West Asia conflict, uncertainty surrounding AI innovation, interest-rate increases, rising crude oil prices, and depreciation of the INR against the USD.

The Key Takeaway for Investors

A broad-market index such as the Nifty 50 does provide diversification, but investors should not assume that diversification means their money is evenly spread across all sectors. A significant portion of the index remains concentrated in a handful of heavyweight industries.

Therefore, when these major sectors experience sharp movements, the entire index can also become more volatile. Nifty 50 diversification reduces concentration at the individual-stock level, but sector concentration can still influence overall portfolio performance.

Conclusion

Summing up the point: an index fund is indeed concentrated with limited sector diversification, but these factors are market realities to understand rather than direct investment advice. Always evaluate tracking error, sector weightings, and risk tolerances when constructing your portfolio.