S&P Index Addition: Stock Price Increase on addition to S&P500
Addition of a stock to S&P Index leads to an increase in the price of the stock - sometimes by upto 15% within a day. During Sept-2018 to Aug-2025, about 800 stocks were added to the S&P indexes(including movement of stocks from one index to another). In this research, we provide the potential return from buying stocks added to S&P indexes and how to use our Alerts ( or Notifications) on Phone & email to learn about these additions before others & make these trading decisions.
01
Average 6.4% Return from Stocks Added to S&P500 between 2018-Sept to 2025-Aug
An average 6.4% price swing per stock in just over a day — compounded across 96 additions to the S&P 500 between September 2018 and August 2025 — translates into a jaw-dropping 612% cumulative return. To put that in perspective, the S&P 500 index itself returned only about 150% over the same period, and even Warren Buffett’s Berkshire Hathaway — the gold standard of long-term investing — delivered far less. Achieving 612% in seven years isn’t just beating the market; it’s multiplying it several times over. In a world where fund managers celebrate a few percentage points of annual “alpha,” these index-inclusion surges reveal a rare, structural opportunity that has outperformed virtually every conventional benchmark by a wide margin.
Based on analysis of 96 stocks that were added to S&P500 Index between September-2018 and August-2025, we found that the these stocks underwent a price change of 6.4% - from the “minimum price during the first five minutes after announcement of addition to index” to the “maximum price reached by the end of next trading day(after hours trading)”. The total return from this price swing of these 96 stocks was 612%.
Company Name | Ticker | Announced Date | Effective Date | Source Index | Final Index | % Highest Change by Next Day Close |
|---|---|---|---|---|---|---|
Block | XYZ | 07/17/2025 | 07/22/2025 | None | S&P 500 | 11.76 |
The Trade Desk | TTD | 07/13/2025 | 07/17/2025 | None | S&P 500 | 15.94 |
Datadog | DDOG | 07/01/2025 | 07/08/2025 | None | S&P 500 | 16.08 |
Coinbase Global | COIN | 05/11/2025 | 05/18/2025 | None | S&P 500 | 25.59 |
Williams-Sonoma | WSM | 03/06/2025 | 03/23/2025 | S&P MIDCAP 400 | S&P 500 | 2.19 |
DoorDash | DASH | 03/06/2025 | 03/23/2025 | None | S&P 500 | 9.42 |
Expand Energy | EXE | 03/06/2025 | 03/23/2025 | S&P MIDCAP 400 | S&P 500 | 3.59 |
TKO Group Holdings | TKO | 03/06/2025 | 03/23/2025 | S&P MIDCAP 400 | S&P 500 | 5.05 |
Lennox International | LII | 12/18/2024 | 12/23/2024 | S&P MIDCAP 400 | S&P 500 | 1.14 |
Workday | WDAY | 12/05/2024 | 12/23/2024 | None | S&P 500 | 9.35 |
Apollo Global Mgt | APO | 12/05/2024 | 12/23/2024 | None | S&P 500 | 6.59 |
Texas Pacific Land | TPL | 11/21/2024 | 11/26/2024 | S&P MIDCAP 400 | S&P 500 | 17.41 |
Amentum | AMTM | 09/23/2024 | 09/29/2024 | None | S&P 500 | 3.23 |
Dell Technologies | DELL | 09/05/2024 | 09/22/2024 | None | S&P 500 | 10.49 |
Palantir Technologies | PLTR | 09/05/2024 | 09/22/2024 | None | S&P 500 | 14.76 |
Erie Indemnity | ERIE | 09/05/2024 | 09/22/2024 | S&P MIDCAP 400 | S&P 500 | 7.26 |
GoDaddy | GDDY | 06/06/2024 | 06/23/2024 | S&P MIDCAP 400 | S&P 500 | 5.8 |
CrowdStrike Holdings | CRWD | 06/06/2024 | 06/23/2024 | None | S&P 500 | 10.56 |
KKR & Co | KKR | 06/06/2024 | 06/23/2024 | None | S&P 500 | 11.39 |
Vistra | VST | 05/02/2024 | 05/07/2024 | None | S&P 500 | 6.34 |
% Change by Next Day Close = % Change [ Maximum of [High Price between Announce Date_17:15 hrs EST & Announce Date+1_19:59 hrs EST] / Minimum of [Low Price on Announce Date betw 17:15 & 17:20 hrs EST] ]
There were 112 S&P 500 additions between 2018-Sept to 2025-Aug. We analyzed the percentage return from the regular-market close immediately preceding the S&P addition announcement to the 4:00 PM ET close on the next trading day.
Of the 112 stocks, 110 stocks had usable data / observations. Data for 2 stocks were missing. The following summary is based on the observed data for 110 stocks.
Statistic | S&P 500 Additions |
|---|---|
Exactly zero | 0 |
Negative | 32 / 110 = 29.1% |
Positive | 78 / 110 = 70.9% |
Maximum | +24.69% |
Minimum | −16.19% |
95th percentile | +11.51% |
5th percentile | −4.07% |
90th percentile | +8.28% |
10th percentile | −3.15% |
75th percentile | +5.61% |
25th percentile | −0.56% |
Standard deviation | 5.40% |
Valid observations | 110 |
Average return | +2.75% |
Median return | +2.20% |
The 5%-trimmed mean is +2.56%, meaning that even after removing observations from both extreme tails, the average remains substantially positive.
The most important findings
1. The typical S&P 500 addition gained about 2–3% by the next close.
The mean is +2.75% and median +2.20%. The proximity of those two numbers is important: the positive average isn't simply the result of one or two extraordinary winners. The 5%-trimmed mean of +2.56% reinforces that conclusion.
2. About 71% of the S&P 500 additions were positive
That's 78 of 110 observations. Roughly 7 out of every 10 stocks therefore finished the next trading day above the regular-market closing price immediately preceding the announcement.
But 29% were negative. Positive reactions were considerably more common;
3. The distribution is quite wide
The middle 50% of observations falls approximately between:
−0.56% and +5.61%
And approximately 80% falls between:
−3.15% and +8.28%
So although the average is +2.75%, individual outcomes vary substantially.
How frequently were the gains or losses large?
The distribution is particularly useful for understanding the economic significance
Next-day Return Number | Number | % of Observations |
|---|---|---|
≤ −10% | 1 | 0.9% |
≤ −5% | 4 | 3.6% |
≤ −3% | 12 | 10.9% |
≥ +10% | 8 | 7.3% |
≥ +5%
| 34 | 30.9% |
≥ +3% | 48 | 43.6% |
≥ +2% | 58 | 52.7% |
≥+1% | 65 | 59.1% |
Nearly one-third (30.9%) of the S&P 500 additions gained at least 5% by the next trading day's close.
At the same time, only 3.6% declined 5% or more.
That asymmetry is more informative than the +2.75% average by itself.
Extreme observations
1. The largest positive observations in the dataset include:
Company | Ticker | % change by Next Day Close |
|---|---|---|
Coinbase Global | COIN | +24.69% |
EPAM Systems | EPAM | +17.94% |
Datadog | DDOG | +15.27% |
Bunge | BG | +14.48% |
Texas Pacific Land | TPL | +14.15% |
2. The largest negative observations include:
Company | Ticker | % change by Next Day Close |
|---|---|---|
PHINIA | PHIN | -16.19% |
Solventum | SOLV | -7.27% |
Nordson | NDSN | -5.78% |
Amentum | AMTM | -5.12% |
Carrier Global | CARR | -4.79% |
Statistical strength of the average
For the 110 observations:
-
Standard error of mean: 0.515 percentage points
-
Conventional 95% confidence interval for mean: approximately +1.73% to +3.77%
That's a useful result. Even allowing for sampling variation under the usual assumptions, the estimated mean remains comfortably above zero.
There are caveats to interpreting this as causal evidence, however. These observations aren't necessarily independent random draws, and market conditions, announcement clustering, company-specific news and other factors can affect returns.
The confidence interval is a statistical description of the historical sample rather than proof that future S&P 500 additions have a particular expected return
An important comparison with our entire dataset
Previously, when we calculated “percentage return from the regular-market close immediately preceding the S&P addition announcement to the 4:00 PM ET close on the next trading day” across all S&P 500/400/600 additions combined, our findings were:
779 observations
+3.80% mean
+3.53% median
75.2% positive
For S&P 500 alone, we now have:
110 observations
+2.75% mean
+2.20% median
70.9% positive
That's a potentially important finding:
The S&P 500 additions in our dataset actually have a lower next-day announcement return than the overall population of S&P index additions.
That supports the point we've been developing around our AXTI/S&P SmallCap 600 testimonial: investors shouldn't necessarily pay attention only to S&P 500 additions. Our own historical dataset suggests meaningful announcement reactions also occur in the MidCap 400 and SmallCap 600.