Index change event
S&P 500 & MidCap 400 Additions & Index Changes: RDDT & SUI – 13th August 2026
On 13 August 2026, S&P Dow Jones Indices announced 4 index changes affecting 4 companies in the S&P 500 and S&P MidCap 400. The most notable move was Reddit joining the S&P 500.
Announced
2026-08-13
Effective
August 17, 2026 at 5:00:00 PM
Indexes Affected
S&P 500, S&P MidCap 400
4
Index Changes in Total
2
Additions
2
Deletions
0
Companies that changed index
What happened to the prices
By the next day's close, the 2 additions with price data had peaked at an average of +10.07%, against +0.74% for the 2 deletions. The largest mover was Reddit, with a peak of +16.46%. The moves are measured from the first extended-hours price after the 17:15 ET announcement.
Webster Financial went against the other deletion: its next-day open was -0.72% from the first price after the announcement, while the 2 deletions averaged +0.07%.
In Short
4 index changes: 2 additions and 2 deletions.
No company moved between indexes, and the changes took effect on 2 dates.
Largest peak move: Reddit, +16.46% by the next day's close.
The changes, index by index
An empty cell means the company was not in the S&P family before, or left it.
S&P 500 Additions: Reddit (RDDT)
1 company joined the S&P 500 and 1 left, effective 18 August 2026. Reddit is new to the S&P family and AvalonBay Communities left the S&P family. Reddit peaked at +16.46% by the next day's close.
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
Reddit | RDDT | S&P 500 | 08/18/2026 |
S&P MidCap 400 Additions: Sun Communities (SUI)
1 company joined the S&P MidCap 400 and 1 left, effective 20 August 2026. Sun Communities is new to the S&P family and Webster Financial left the S&P family. Sun Communities peaked at +3.67% by the next day's close.
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
Sun Communities | SUI | S&P MidCap 400 | 08/20/2026 |
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
Price reaction
The close price is the last price before the announcement. All percentages are measured from the open price 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 | S&P 500 | 158.12 | 158.24 | +8.94% | +10.19% | +12.36% | +11.08% | +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 | S&P MidCap 400 | 120.19 | 121.10 | +2.04% | +1.92% | +1.92% | +2.35% | +3.67% |
S&P SmallCap 600 Additions Changes
Not a Investment Advice
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 |
|---|---|---|---|---|---|---|---|---|---|---|
Not a Investment Advice
This page is research about past price behaviour. It is not a recommendation to buy or sell.