Index change event
S&P SmallCap 600 Additions & Index Changes: ACMR – 22nd September 2025
On 22 September 2025, S&P Dow Jones Indices announced 2 index changes affecting 2 companies in the S&P SmallCap 600. ACM Research replaced WK Kellogg in the S&P SmallCap 600.
Announced
2025-09-22
Effective
September 25, 2025 at 5:00:00 PM
Indexes Affected
S&P SmallCap 600
2
Index Changes in Total
1
Additions
1
Deletions
0
Companies that changed index
What happened to the prices
By the next day's close, ACM Research, the only addition with price data, had peaked at +7.70%, against +0.08% for WK Kellogg, the only deletion with price data. The moves are measured from the first extended-hours price after the 17:15 ET announcement.
With one addition and one deletion priced, there is no group to stand out from: ACM Research opened the next day at +4.86% and WK Kellogg at +0.04%, both from the first price after the announcement.
In Short
2 index changes: 1 addition and 1 deletion.
No company moved from one S&P index to another in this announcement.
Largest peak move: ACM Research, +7.70% 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.
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
S&P SmallCap 600 Additions: ACM Research (ACMR)
1 company joined the S&P SmallCap 600 and 1 left, effective 26 September 2025. ACM Research is new to the S&P family and WK Kellogg left the S&P family. ACM Research peaked at +7.70% by the next day's close.
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
ACM Research | ACMR | S&P SmallCap 600 | 09/26/2025 |
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 |
|---|---|---|---|---|---|---|---|---|---|---|
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 |
|---|---|---|---|---|---|---|---|---|---|---|
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 |
|---|---|---|---|---|---|---|---|---|---|---|
ACM Research | ACMR | S&P SmallCap 600 | 36.68 | 37.00 | +2.30% | +2.84% | +3.46% | +4.86% | +7.70% |
Not a Investment Advice
This page is research about past price behaviour. It is not a recommendation to buy or sell.