Index membership history
Who was in the FTSE 100, FTSE 250, S&P 500 and Russell 1000 on any day, with every change as it was announced.
A backtest run on today's index members is survivorship-biased. ORTEX rebuilds the membership of each index day by day from the index providers' own publications: every addition and deletion with the date it took effect, the date it was announced where one was published, the review or corporate event behind it and a confidence label. Former members stay in the history after they stop trading, and are linked to ORTEX ids wherever ORTEX holds the company.
members in the FTSE 100 at every one of its 171 review dates since 1984, and 250 in the FTSE 250 at all 136 reviews since its launch in 1992. The history adds up.
Member counts checked on the ORTEX index membership history, November 2026.
Backtests on the members an index actually had on each date, free of survivorship bias.
Every past review with its announcement and effective dates, to study the trade around them.
A dated record of each index's membership, with a confidence label on every change.
Every member, on every day
Point-in-time membership and every change, for four of the most traded equity indices.
The members of an index on any date since its history starts, each with the date it joined. A date before the history returns nothing, never today's list.
Each addition and deletion with its effective date and, where the provider or the press published one, its announcement date, the review it belongs to and the reason: a review, takeover, demerger, spin-off, IPO or other event.
The index providers' own notices and factsheets first, then regulatory news and historical press, with index fund holdings and filings as cross-checks, reconciled by ORTEX's proprietary process. A rename is not a change.
Companies since taken over, merged or delisted stay in the history under the name and ticker they had, with ISIN and SEDOL where the sources give them and ORTEX company, security and listing ids where ORTEX holds the company.
Each member's periods in the index, with the start and end dates and the reason for each, ready to join against prices and returns.
A high, medium or low label on every change, from how well the sources agree. S&P 500 changes before 2010 are rebuilt from historical lists and labelled accordingly. Corrections are flagged on incremental pulls, never silently dropped.
The membership each index actually had on each day, reconciled from the providers' own publications and checked against the index size at every review.
Sample changes
Recent additions and deletions as the API serves them, June to November 2026.
- Read
- Live enterprise API, 5 November 2026
- Also on every row
- The review, ISIN, SEDOL, ORTEX ids and the kinds of source behind the change
- Checked
- FTSE 100 at 100 members on all 171 review dates; FTSE 250 at 250 on all 136; Russell 1000 within its tolerance at all 29 reconstitutions
Okta's addition to the S&P 500 was announced on 30 October and took effect on 4 November. Both dates are on the row, so a study of the trade around a change can start from the day the market knew.
| Index | Announced | Effective | Action | Company | Ticker | Reason | Confidence |
|---|---|---|---|---|---|---|---|
| FTSE 100 | 2 Sep 2026 | 21 Sep 2026 | Add | Easyjet | EZJ | Review | High |
| FTSE 100 | 2 Sep 2026 | 21 Sep 2026 | Delete | Persimmon | PSN | Review | High |
| FTSE 100 | 24 Sep 2026 | 1 Oct 2026 | Delete | Schroders | SDR | Takeover | High |
| FTSE 100 | 28 Sep 2026 | 1 Oct 2026 | Add | WPP | WPP | Takeover | High |
| FTSE 250 | 15 Oct 2026 | 20 Oct 2026 | Add | EnQuest | ENQ | Other | High |
| S&P 500 | 4 Sep 2026 | 21 Sep 2026 | Add | Bloom Energy | BE | Review | High |
| S&P 500 | 4 Sep 2026 | 21 Sep 2026 | Delete | The Trade Desk | TTD | Review | High |
| S&P 500 | 30 Oct 2026 | 4 Nov 2026 | Add | Okta | OKTA | Takeover | High |
| S&P 500 | 30 Oct 2026 | 4 Nov 2026 | Delete | Kenvue | KVUE | Takeover | High |
| Russell 1000 | 4 Sep 2026 | 21 Sep 2026 | Add | Quantinuum | QNT | IPO | High |
Announced is the day the change was published; effective is the first trading day it applies, the first day in for an addition and the first day out for a deletion. Every row also carries the member's ISIN, SEDOL, ticker at the time and ORTEX ids where linked.
License index membership history for your desk.
Trial access, pricing and licensing from the data sales team. Delivered over the enterprise API (coverage, the members on any date, every change with an incremental feed, and membership spells), as JSON or CSV, licensed per index.
Pre-earnings briefs two to three days ahead, surprises and past reactions.
Dividends, splits, M&A, spin-offs and lock-ups on one timeline per stock.
Every expected dividend for 54,000+ listings: dates, amount range and cut or raise chances, daily.
585,000 company events a year and a global macro calendar with surprises.
Daily add and delete forecasts for 131 indices in 22 markets, MSCI included, scored after every review.
ORTEX Technologies Ltd, 26-27 Bedford Square, London WC1B 3HP. Registered in England and Wales, company number 11033216. Coverage, history and figures are as at November 2026. Provided for information purposes only; not investment advice, a personal recommendation, or an offer to buy or sell any security. Past performance is not a guide to future results. ORTEX does not guarantee the accuracy or completeness of any data or forecast. Index names are the trade marks of their owners; ORTEX is not affiliated with or endorsed by any index provider. See the full data catalog.