Reddit Joins the S&P 500 on Aug 18: Shares Pop 8.8%
S&P Dow Jones Indices adds Reddit (RDDT) to the S&P 500 effective Aug 18, 2026. Shares jumped 8.8% after-hours as passive funds prepared to buy.
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The Index Effect: How S&P 500 Additions Move Stocks
How S&P 500 inclusion moves a stock: the pre-announcement drift, run-up to effective date, decay after, and why the effect has shrunk since 2010.
S&P 500 Top-10 Concentration Hits 37%, Beating Dot-Com Peak
The S&P 500’s 10 largest stocks now command roughly 37% of the index — exceeding the 2000 dot-com peak. Here’s the data and what it means.
S&P 500 Inclusion: What Really Happens When a Stock Joins
How a stock actually gets added to the S&P 500, what the historical “index effect” was, and why recent research finds that pop has largely vanished.
Russell 2026 Reconstitution: A $217B Day, Now Semi-Annual
FTSE Russell’s preliminary 2026 additions and deletions hit on May 22. The flip goes effective after the June 26 close – and now happens twice a year.
SanDisk Soars 12% on Nasdaq-100 Entry: The Index Effect Explained
SanDisk surged 11.83% on Nasdaq-100 inclusion news. Here’s the capital markets mechanics behind why index additions reliably move stock prices.