S&P 500: The Winners and Losers of May 2026
S&P 500: The Winners and Losers of May 2026
May 2026 delivered a 5.5% gain for the S&P 500, though the month’s returns were far from evenly distributed. Out of the 500 index constituents, 215 ended May in positive territory, while the remaining 286 closed the month in the red — meaning the majority of stocks actually declined even as the index advanced. The month’s biggest winners were all tied to AI infrastructure, servers, and cloud software, while the worst performers faced company-specific setbacks that outweighed any benefit from the broader market. In this article, we break down the top winners and losers in the S&P 500 for May 2026 and examine the key drivers behind their stock movements.
Top S&P 500 Performers in May
Among the top performers were Dell Technologies ($DELL), Micron Technology ($MU), and Datadog ($DDOG). Here’s a closer look at why each of these stocks stood out:
Dell Technologies ($DELL) +101.44%
Dell Technologies, a technology company that designs and sells servers, PCs, storage systems, and IT infrastructure for enterprise and government customers, more than doubled in May as a blowout earnings report and a sharply raised full-year outlook drove one of the largest single-month moves in the stock’s history.
The month opened with a corporate governance announcement. On May 4, Dell’s board unanimously approved a plan to redomicile the company to Texas, a decision the company described as better aligned with its long-term operational and strategic interests. The move had limited immediate impact on the stock but signaled continued focus on corporate efficiency.
Mid-month brought product news. On May 19, at its annual Dell Tech World conference, the company unveiled a new generation of AI-era data center products, including the PowerStore Elite storage system and updated compute platforms built specifically for modern AI workloads. According to the company, these systems are designed to accelerate inferencing and large-scale model training across enterprise environments.
The decisive catalyst came after markets closed on May 28. Dell reported first-quarter fiscal year 2027 results that came in well ahead of expectations: revenue of $43.8 billion, up 88% year over year, and diluted earnings per share of $5.24, up 282% from the same period a year earlier. Management raised its full-year AI server revenue target to $60 billion and lifted its annual sales and earnings guidance. Reuters also reported that Dell secured a $9.7 billion Department of Defense contract during the same period, adding a significant government customer to its revenue base.
Micron Technology ($MU) +87.76%
Micron Technology, a semiconductor company that manufactures memory chips including DRAM and NAND flash used in data centers, PCs, and AI systems, surged nearly 88% in May as a series of product launches, new U.S. manufacturing capacity, and a major analyst upgrade reinforced its standing as a critical supplier for AI infrastructure.
The month began with a product milestone. On May 5, Micron announced it had begun shipping the world’s highest-capacity commercially available solid-state drive, a 245TB enterprise SSD from its 6600 ION line. According to the company, the drive is designed for AI and cloud workloads that require extreme storage density in space-constrained data center environments.
On May 12, Micron sampled a 256GB DDR5 server memory module built on its most advanced manufacturing node, capable of running at speeds up to 9,200 megatransfers per second. The company said the module is aimed at AI infrastructure customers that need higher memory capacity per server to run large language models and other demanding workloads.
The domestic manufacturing story added another dimension. On May 22, Micron announced it had begun production of leading-edge DRAM at its Virginia fab, describing the milestone as the start of high-volume advanced memory manufacturing on U.S. soil — a development that resonated with investors focused on supply chain resilience.
The combination of supply constraints and surging demand from the AI buildout provided a powerful backdrop for a stock that had already made significant gains earlier in the year.
Datadog ($DDOG) +87.12%
Datadog, a cloud-based monitoring and security platform used by software and technology companies to track the performance of their applications and infrastructure, surged more than 87% in May after reporting a quarter that beat expectations on every major metric and raising its full-year financial targets by a wider margin than analysts had anticipated.
On May 7, Datadog reported first-quarter 2026 results: revenue of $1.006 billion, up 32% year over year, and free cash flow of $335 million. The company reported adjusted earnings per share of $0.60, compared to the $0.51 analysts had expected. According to the company, growth was driven by expanding usage among enterprise customers, increased adoption of its security and AI observability products, and continued strength in cloud-native software development environments.
Guidance was the most important element of the release. Management raised its second-quarter revenue forecast to a range of $1.07 billion to $1.08 billion, well above the approximately $961 million analysts had been expecting. The company also lifted its full-year revenue and earnings targets. During the same period, Datadog announced it had received FedRAMP High authorization for its government platform, making its monitoring tools available to U.S. federal agencies with the highest security requirements — an expansion that opens a new and sizable customer segment for the company.
Worst S&P 500 Performers in May
Among the biggest decliners in the S&P 500 for May 2026 were Zoetis ($ZTS), AutoZone ($AZO), and Dow Inc. ($DOW). Each faced distinct pressures — from a guidance cut tied to slowing pet health demand, to margin compression from inventory accounting, to broad macro headwinds in the chemicals sector — that weighed heavily on their stocks even as parts of the broader market advanced. Here’s a closer look at what drove their underperformance.
Zoetis ($ZTS) -32.43%
Zoetis, a pharmaceutical company focused on medicines and vaccines for companion animals and livestock, fell more than 32% in May after reporting a quarter that missed analyst expectations and lowering its financial targets for the full year.
On May 7, Zoetis reported first-quarter 2026 results: total revenue of $2.3 billion, up 3% year over year, but roughly flat on an organic basis after adjusting for currency effects. Adjusted earnings per share of $1.53 came in below the $1.61 analysts had forecast. According to the company, the quarter unfolded in a more challenging environment characterized by a decline in veterinary visits, price sensitivity among pet owners, and intensifying competition in certain product categories.
The guidance revision was the sharper blow. Management lowered its full-year 2026 revenue forecast to a range of $9.68 billion to $9.96 billion and cut its adjusted earnings per share target to $6.85 to $7.00, down from a prior range of $7.00 to $7.10. The company cited softer demand in its U.S. companion animal business, where revenue fell approximately 11% during the quarter, as the primary driver of the reduction. Reuters reported that aggressive pricing from rivals added to the pressure.
AutoZone ($AZO) -20.76%
AutoZone, a retailer of automotive replacement parts and accessories operating more than 7,000 stores across the United States and internationally, fell more than 20% in late May after reporting quarterly results that included a margin figure that came in below what investors had expected.
On May 26, AutoZone reported fiscal third-quarter 2026 results: net sales of $4.84 billion, up 8.4% year over year, same-store sales growth of 3.9%, and diluted earnings per share of $38.07, up from $35.36 a year earlier. On the surface, the numbers looked solid. However, the gross profit margin of 52.2% — down 57 basis points compared to the prior year — became the focal point for investors.
According to the company, the margin decline was driven primarily by a 77 basis point headwind from a LIFO inventory accounting charge, a method that assumes the most recently acquired — and often more expensive — inventory is sold first. Reuters highlighted that inventory levels rose approximately 10.8% during the quarter, and that the associated accounting impact surprised analysts who had expected margins to hold more steady. Despite the strong top-line growth and an earnings beat, the market focused on what the margin contraction might signal about the company’s cost trajectory going forward.
Dow Inc. ($DOW) -16.65%
Dow Inc., a global materials science company that produces chemicals, plastics, and coatings used across industries including packaging, construction, and consumer goods, declined more than 16% in May without any meaningful company-specific announcement to explain the move.
Dow’s most recent quarterly results came from April 23, when the company reported first-quarter 2026 net sales of $9.8 billion, down 6% year over year, and an adjusted operating loss of $0.14 per share. The results reflected ongoing pressure on chemical pricing and volumes across core end markets. No material press releases, contract announcements, or strategic updates were issued by the company during May itself.
Instead, Dow’s performance during the month was shaped by macro forces. Brent crude oil prices declined roughly 5% in late May, reducing the value of petrochemical feedstocks and weighing on investor sentiment across the energy and materials sector. Analysts noted that the margin improvement Dow and its peers had benefited from in prior quarters was showing signs of fading, and that a softening demand environment for specialty chemicals could pressure the company’s results heading into the second half of the year.
What the Month Really Said
May’s dispersion followed a clear pattern. The winners were companies sitting at key bottlenecks in the AI buildout: servers, memory, and cloud observability software. The losers were businesses facing a meaningful reset in how investors thought about demand durability and cost structure — a guidance cut at Zoetis driven by fewer vet visits and pricing pressure, margin compression from inventory accounting at AutoZone, and macro-driven petrochemical weakness at Dow. The biggest moves were not random. They were tied to specific disclosures that changed how the market assessed future earnings power, competitive position, or operating risk. The fact that 286 out of 500 stocks declined in a month the index gained 5.5% underscores just how concentrated the May rally really was.
This article is for informational purposes only and is not investment advice or a solicitation to buy or sell securities. The content is based on publicly available information and reflects the author’s opinions as of the publication date, which may change without notice. All investments carry inherent risks, including the potential loss of principal, and past performance is not indicative of future results. Readers should conduct their own research or consult a financial advisor before making investment decisions. BBAE holds no position in the securities mentioned, nor are they compensated by the companies mentioned.
