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13th August 2026 S&P Additions & Index Changes
The latest S&P index changes include additions to the S&P 500 and S&P MidCap 400. Reddit Inc. (RDDT) will replace AvalonBay Communities (AVB) in the S&P 500 effective August 18, while Sun Communities (SUI) will replace Webster Financial (WBS) in the S&P MidCap 400 effective August 20. The changes follow pending acquisitions involving AvalonBay Communities and Webster Financial. Below are the latest S&P 500 and S&P MidCap 400 additions, their effective dates, Source indexes and stock-price reactions following the announcement.
S&P 500 Additions
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
Reddit | RDDT | None | S&P 500 | 18/08/2026 |
S&P 400 Additions
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
Sun Communities | SUI | None | S&P MidCap 400 | 20/08/2026 |
How Did the S&P 500 Additions React After the Announcement?
S&P 500 Additions Changes
Company | Ticker | Source Index | Final Index | Close Price | Open Price at Announcement | % Change + 5 min | % Change + 30 min | % Change at 20:00 Hrs | % Change by Next Day Open | % Highest Change by Next Day Close |
|---|---|---|---|---|---|---|---|---|---|---|
Reddit | RDDT | None | S&P 500 | 158.0500 | 158.2400 | 8.54% | 9.90% | 12.36% | 10.91% | 16.46% |
S&P MidCap 400 Additions Changes
Company | Ticker | Source Index | Final Index | Close Price | Open Price at Announcement | % Change + 5 min | % Change + 30 min | % Change at 20:00 Hrs | % Change by Next Day Open | % Highest Change by Next Day Close |
|---|---|---|---|---|---|---|---|---|---|---|
Sun Communities | SUI | None | S&P MidCap 400 | 120.1900 | 121.1000 | 2.04% | 1.92% | 2.35% | 3.67% |
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