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What lies beneath the headline names in the S&P 100?

Introducing the S&P 100 Ex-Top 20 Select Index, which measures the performance of companies within the S&P 100, excluding the largest 20 constituents ranked by float-adjusted market capitalization. This blog examines the depth, diversification and shifting leadership that can be obscured by the dominance of the very largest names.

The “Next 80” Make Up a USD 13.4 Trillion Segment

As shown in Exhibit 1, the companies outside the largest 20 make up a USD 13.4 trillion segment, over twice the size of Japan’s equity market and nearly four times larger than the U.K. market and the U.S. mid-cap segment (as measured by the S&P MidCap 400^®). Far from a niche slice of the U.S. equity landscape, the “next 80” represent a major portion of the global equity opportunity set.

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Beyond its global scale, comparing this segment with the S&P 100 offers additional insight. While the top 20 names often dominate market headlines, the remaining 80 companies represent a meaningful share of the mega-cap U.S. equity segment. Since 2001, these companies have accounted for approximately 45% of the S&P 100’s total weight on average, ranging from 32% to 56% (see Exhibit 2). This variability reflects shifts in mega-cap leadership and reinforces the concept of examining the “next 80” as a distinct lens.

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The S&P 100 Ex-Top 20 Select Index offers a more evenly distributed profile compared with the S&P 100, which is heavily concentrated in its largest names. Exhibit 3 shows that the top decile of constituents accounted for 55% of the S&P 100’s weight, versus about 22% in the S&P 100 Ex-Top 20 Select Index. This shows how steeply weight accumulates at the top of the S&P 100, highlighting the extent to which its performance can be driven by a relatively small set of names.

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Broadening the Sector Profile

Differences in index size and constituent concentration are also reflected in sector weights. As shown in Exhibit 4, Information Technology represents nearly 25% of the S&P 100 Ex-Top 20 Select Index, well below the 42% weight in the S&P 100. This lower weight in Tech is paired with greater representation across other sectors, most notably Health Care (18%), Financials (17%) and Industrials (14%). Removing the largest 20 names resulted in a more balanced sector profile, reducing concentration in a few dominant sectors and broadening representation across the drivers of mega-cap U.S. equity performance. While the S&P 100’s Tech weight rose from about 20% in 2010 to over 40% in 2025, the S&P 100 Ex-Top 20 Select Index increased moderately from roughly 9% to about 20%. Meanwhile, sectors such as Health Care, Financials, Industrials and Materials had higher weights in the S&P 100 Ex-Top 20 Select Index.

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Performance trends aligned with each index’s sector composition. The S&P 100 outperformed in recent years as concentrated mega-cap Tech leadership led performance, while the S&P 100 Ex-Top 20 Select Index tended to hold up better during periods when market leadership broadened.

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Conclusion

The S&P 100 Ex-Top 20 Select Index offers a complementary lens on the S&P 100 by highlighting a large, diversified segment beyond the top 20 names. Its meaningful scale and broader sector mix provide additional perspective on the composition, concentration dynamics and long-term characteristics of the mega-cap U.S. equity landscape.

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