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The S&P 500 index: history, rules and the next additions
The S&P 500 is the world's most followed stock index — around 500 of the largest US companies, weighted by market value and maintained by a committee at S&P Dow Jones Indices. Because so much money tracks it, joining the index is one of the biggest events in a stock's life. This page gathers its history, the eligibility rules, the review calendar and the latest additions.
A short history
The Composite Index
Standard Statistics Company launches a weekly index of 233 US companies, expanding to a daily 90-stock index in 1926 — the direct ancestor of the S&P 500.
Expansion to 500 stocks
On March 4, 1957 the index grows to 500 large US companies chosen by committee to represent the whole economy — the S&P 500 as we know it is born.
First index fund
Vanguard launches the First Index Investment Trust, the first fund letting ordinary investors buy the entire S&P 500 in a single trade.
Futures trading begins
CME lists S&P 500 futures, making the index the reference for hedging US equity exposure worldwide.
SPY, the first US ETF
The SPDR S&P 500 ETF Trust (SPY) lists in January 1993 and goes on to become the most traded security on earth. IVV and VOO follow the same index.
Float adjustment
S&P switches the index to float-adjusted market-cap weighting, counting only shares actually available to public investors.
The benchmark
The S&P 500 covers roughly 80% of US equity market value and tens of trillions of dollars are benchmarked or indexed to it — which is why every addition moves prices.
The eligibility rules
To join the S&P 500, a stock must pass every screen below — and then still be picked by the index committee. The thresholds evolve over time; check S&P Dow Jones Indices' methodology document for the current exact figures.
A US company
The issuer must be a US company — incorporated in the US, primarily listed on a US exchange (NYSE, Nasdaq or Cboe) and filing with the SEC.
Large enough
A minimum market value of listed equity applies, which S&P raises periodically as the market grows — roughly $18 billion in recent years. In practice, additions are usually far larger.
Profitable
GAAP earnings must be positive in the most recent quarter and over the trailing four quarters combined. Loss-making giants still get turned away.
Liquid
The stock must trade enough value relative to its size, with a meaningful share price — penny stocks and thinly traded names are ineligible.
Public float
At least 10% of shares must be available to public investors, and recent IPOs generally need about 12 months of trading history before they can be considered.
Committee selection
Unlike mechanical indexes, a committee makes the final call. Meeting every rule makes a stock eligible, not guaranteed — sector balance and representation also matter.
Review calendar
The S&P 500 rebalances quarterly, effective after the close on the third Friday of March, June, September and December. Constituent changes are also announced ad hoc — usually with just a few days' notice — when companies are acquired, shrink or grow into eligibility.
Sep 18, 2026
Quarterly rebalance
Quarterly rebalance effective after the close.
Dec 18, 2026
Quarterly rebalance
Quarterly rebalance effective after the close.
Mar 19, 2027
Quarterly rebalance
Quarterly rebalance effective after the close.
Jun 18, 2027
Quarterly rebalance
Quarterly rebalance effective after the close.
Recent additions
The latest companies to join the S&P 500. Click any name for its stock page with day-by-day performance since inclusion.
Last column: 1-month return relative to the S&P 500 itself. See every addition with full returns