The S&P 500 inclusion effect springboard is back in a big way

That temporary price bump had cooled throughout the 2010s — now it’s heating up again, per a new Goldman Sachs report.

7/24/25 11:48AM

It’s not unusual to see shares pop when a company is set to join the S&P 500, an index now linked to a staggering $20 trillion in global assets. Just last Friday, Block soared 10% after its inclusion was announced, while Datadog spiked 15% on similar news earlier this month.

Known as the “S&P 500 Index Effect,” this short-lived bump is fueled in part by fresh demand from $13 trillion worth of passive funds and ETFs tracking the benchmark, which are required to buy shares of newly added companies.

But over the past decade, this effect had been losing steam. According to a 2023 Harvard study, the average announcement day return for S&P 500 additions dropped from 9.4% in the 1990s to just 0.8% by the late 2010s — partially because markets got better at absorbing these shocks, and traders got better at predicting inclusions.

Now, though, a new Goldman Sachs analysis suggests the inclusion effect may be staging a comeback.

Since 2021, stocks newly added to the S&P 500 have outperformed the equal-weighted index by an average of 4 percentage points on the announcement day — with nearly three-quarters of those stocks beating the benchmark.

Source matters

One factor driving the revival is that fewer companies are migrating from the S&P MidCap 400 Index. Per Goldman’s estimate, stocks added from outside the S&P 400 have seen average relative gains of 5.3 pp since 2013, while those graduating from the midcap index actually dipped 0.4 pp.

Retail hype may also be adding fuel, with recent entrants like Coinbase, Super Micro Computer, Palantir, and Datadog already beloved by traders ahead of their debut — and tied to popular themes like AI or crypto.

So, which big names could be next in line for America’s flagship index?

Go Deeper: Datadog is now in the S&P 500. These big stocks still aren’t.

Matt Phillips7h

Oil settles Friday at highest level since start of war

US oil prices moved higher in afternoon trading Friday, sapping strength from the stock market as they posted their highest close since the start of the Iran war.

After another day where the Strait of Hormuz was essentially closed to global tanker traffic, US futures for West Texas Intermediate settled up 3.1% at $98.71 a barrel for an 8.6% weekly gain, per Dow Jones data.

American officials have discussed using the US Navy to escort tankers through the narrow waterway between Iran and Oman, but have said plans for such convoys are not ready yet. However, it is unclear if military convoys would bring an end to the war-related dislocations in the oil market.

“It could help,” Tom Liles, senior vice president of upstream research at energy consulting firm Rystad, told Sherwood News in a recent interview. “It could also go in a lot of different directions if a Navy ship is hit or if a tanker is hit.”

Oil Posts Weekly Gains As Middle East Conflict Drags On

Tasha Matsumoto

Stocks post third straight week of losses as Brent crude surges above $100

Stocks wiped out early gains to close lower amid the ongoing war in Iran.

Matt Phillips11h

Memory stocks rebound off last weeks losses

Memory stocks Micron, Sandisk, Western Digital, and Seagate Technology Holdings rose again Friday, putting these crucial providers of chips for AI inference work on track for big weekly gains after last week’s steep losses following the outbreak of war with Iran.

There’s no obvious trigger for the move higher for these shares this week, other than a bit of a recovery in the AI trade more broadly — AI beneficiaries like IT cable and connections maker Amphenol and custom chip and networking company Marvell Technology clawed back some gains this week — perhaps due Oracle’s earnings earlier, and some mean reversion to boot.

Micron is due to report earnings after the close of trading on Wednesday, with the company catching a couple price target hikes this week, including one from Wedbush on Friday.

Sandisk is something of a different story, as its enormous gains over the last 12 months — roughly 1,200% — have made it a momentum play beloved by the retail crowd.

It was up about 20% this week at around 11 a.m. ET. And its nearly 170% gain this year keeps the stock on top of the S&P 500, in terms of price performance.

Luke Kawa

11h

The S&P 500’s internals are awful... while it’s still less than 5% from its record closing high

The breadth of negative momentum within the index’s constituents is even worse than at the tariff-induced market bottom in April 2025.