Index providers are bracing for a significant wave of initial public offerings (IPOs) expected later this year. Some of these IPOs could potentially be among the largest IPOs ever. As a result, index providers are increasingly looking to balance the need to build benchmarks that represent the entire U.S. equities market with concerns about liquidity, volatility, and free float, which have tended to create challenges for some newly listed stocks.

Index methodologies vary, but historically, most have required new listings to "season" for several months following their entry into the public market. This period gives stocks time to demonstrate their investability before being added to an index. However, per recent announcements from Nasdaq, S&P Dow Jones, and others, some index providers are changing, or considering changing, their rules to allow faster entry for large IPOs.

Of course, changing the rules for an index can be controversial. Advocates for fast entry emphasize the very large sizes of the anticipated IPOs. Since these newly listed stocks could represent a significant slice of the U.S. equities market, they believe indexes should reflect the contributions of these stocks as soon as possible. They also claim that index funds could be left behind if actively managed funds are able to purchase newly listed stocks well before their passive peers.

Critics of potential fast tracking worry that truncating the timeline for index inclusion may create the equivalent of short squeezes, as index-tracking investment vehicles struggle to source newly listed stocks.

While the exact details are complicated (and even indexes offered by the same firm may have different rules), here's how some of the largest index providers are broadly thinking about their inclusion methodologies:

• Nasdaq: Following a public comment period, Nasdaq announced on March 30 that the Nasdaq-100^® Index would change its inclusion criteria on May 1 to allow for faster entry. This index consists of the 100 largest non-financial companies listed on the Nasdaq stock exchange. If an IPO's market cap places it within the top 40 of these companies, the newly listed stock will be added to the index after 15 trading days. Since no other stocks will be removed from the index at the time of the inclusion, the number of constituents could temporarily exceed 100 until the next index reconstitution. Per Nasdaq's published methodology, a security's index weight is capped at the lesser of its full eligible market capitalization or three times its float-adjusted market cap. For example, if a company has 15% float, its weighting would be limited to 45% of its listed market value. Above roughly one-third public float, or 33%, the cap is no longer binding, and securities are effectively weighted at their full market cap.
• S&P Dow Jones: At the end of April, S&P Dow Jones announced that it was also seeking feedback through public consultation on a fast-entry proposal. While the stocks in the S&P 500^® Index are officially selected by a committee, the general requirements for index eligibility are based on publicly available rules. If approved, the following changes to the S&P 500 Index's eligibility rules for mega-cap IPOs would become effective in early June:
  • Stocks would become eligible for the index after six months rather than 12 months.
  • The requirement to have a minimum Investable Weight Factor of 0.10 (roughly at least 10% of shares publicly floated) would be dropped.
  • Companies would not be required to demonstrate profitability. 

Still, S&P Dow Jones reminds market participants that the proposed changes would apply only to index eligibility. The actual inclusion of new constituents remains entirely at the discretion of the index committee. 

• MSCI: MSCI was one of the first index providers to consider fast-entry provisions, which have been part of the firm's methodology documents since 2017. If an IPO meets certain size criteria, it may be added to MSCI's indexes as soon as the close of the tenth day of trading. However, MSCI's standard weighting methodology—free-float-adjusted market capitalization—is designed to help address investability and turnover concerns. In other words, a company that offers only a small percentage of its stock for public trading may not meet market-cap thresholds for index inclusion or it may see its weight in MSCI indexes adjusted downward accordingly.
• Center for Research in Security Prices (CRSP): CRSP indexes were also recently changed to better accommodate fast entry. New IPOs are eligible for CRSP's suite of indexes after five trading days, provided they pass the index's eligibility and investability screens. Previously, these screens included having at least 10% of shares qualifying as freely tradeable (known as float shares outstanding, or FSO). However, in April the methodology changed to allow stocks with either 10% FSO or approximately $3.3 billion in float-adjusted market capitalization to be eligible for index inclusion. The weighting of stocks in CRSP indexes is also based on free float, which should help address the investability challenges associated with thinly traded stocks.
• FTSE Russell: In February 2026, FTSE Russell requested comments on a proposal to allow fast entry for very large IPOs on the fifth trading day, instead of waiting for the next quarterly rebalance, along with other changes related to free float and voting rights. The rationale for these changes, as FTSE Russell stated, is to enable indexes to remain "more representative of the U.S. equity market sooner." The change is also intended to give passive investors exposure to IPOs through index-tracking funds or specialized ETFs. The consultation was extended and closed on April 3, but FTSE Russell has yet to announce the results.

Finally, investors should note that many alternatively weighted indexes, sector indexes, and thematic indexes begin with a broad-based, market-cap-weighted index—such as the S&P 500 Index or the MSCI USA Investable Market Index—as the starting universe of eligible stocks. Fast-entry provisions may flow through to these linked indexes, depending on the policies of the index defined as the starting universe.

With a likely wave of IPOs coming, there's no question the market is eagerly anticipating the big splashes that some of the largest could make. Fortunately, index providers are already considering the challenges and opportunities that massive IPOs may bring. Still, there are plenty of unknowns, and downside volatility may be an issue in the days leading up to giant IPOs as both active and index funds may sell assets in order to reposition their portfolios.