Introduction

The representation of S&P 100^® companies in the S&P 500^® has grown over the past two decades: the blue-chip subset of The 500™ accounted for 70% of the large-cap U.S. equity benchmark’s weight at the end of June 2025, up from 45% at the end of 1998. However, market participants may find it beneficial not to overlook the “other 400” members of the S&P 500, as measured by the S&P 500 Ex-S&P 100 Select Index.

Size: A USD 15 Trillion Market in Its Own Right

The S&P 500 Ex-S&P 100 Select Index measures the performance of S&P 500 companies that are not members of the S&P 100. Far from a niche slice of the U.S. equity market, this segment represents more than USD 15 trillion in market capitalization—larger than the equities markets of Japan, the U.K. or Canada, and many times the size of the S&P MidCap 400^® or S&P SmallCap 600^®. Hence, overlooking the other 400 names in The 500 risks missing a substantial share of the global equity opportunity set.

(Click on image to enlarge)

Sectors: Diversification beyond Mega-Cap Tech

The S&P 500 Ex-S&P 100 Select Index focuses on diversification beyond the blue-chip exposure of the S&P 100, offering broader sector representation and a more balanced perspective on the drivers of large-cap U.S. equity performance.

Exhibit 3 shows that the S&P 500 Ex-S&P 100 Select Index had more balanced sector weights compared to the S&P 100 at the end of June 2025. For example, the index had a lower weight in Information Technology and Communication Services and a much greater weight in Industrials, Real Estate and Utilities.

(Click on image to enlarge)

The difference in sector composition was not just a recent phenomenon: Exhibit 4 shows that the S&P 100 and the S&P 500 Ex-S&P 100 Select Index have had distinct sector weights since the 1990s. While the S&P 100 became increasingly dominated by Information Technology and Communication Services, the S&P 500 Ex-S&P 100 Select Index consistently showed broader representation across GICS^® sectors (see Exhibit 4).

(Click on image to enlarge)

Conclusion

The S&P 500 Ex-S&P 100 Select Index shines a light on the “other 400” large-cap U.S. companies often overlooked by mega-cap dominance. With a market size rivaling that of many countries’ equity markets, and sector weights that broaden perspectives on the drivers of performance, the S&P 500 Ex-S&P 100 Select Index could serve as a complementary lens on U.S. large-cap equities.

More By This Author: