S&P 500 Market Performance: May 2025 Winners and Losers

The S&P 500 staged a significant recovery in May 2025, climbing 6.15% after a turbulent April that saw the index briefly enter bear market territory [1, 3]. While the broader market rally resulted in positive returns for 346 of the index's 500 constituents, nearly 30% of the stocks tracked by the index ended the month in the red [1, 3].

Key takeaways

• NRG Energy led the S&P 500 with a 42.27% gain, bolstered by strong earnings and a $6.4 billion acquisition [3].
• UnitedHealth Group was the index's worst performer, dropping 26.6% amid leadership changes and rising Medicare Advantage costs [1, 2, 3].
• Constellation Energy and Seagate Technology also saw significant growth, rising 37% and 29.56% respectively [3].
• Regeneron Pharmaceuticals shares fell 18.2% following the failure of a phase 3 clinical trial for its experimental COPD drug [1].

Energy and Tech Lead Market Gains

The month’s top performers were driven by strategic acquisitions and the ongoing demand for AI-related infrastructure [3]. NRG Energy surged over 42% after reporting first-quarter adjusted earnings of $2.62 per share and announcing the acquisition of LS Power’s “Premier Power” portfolio [3]. Similarly, Constellation Energy rose 37% as it positioned itself in the clean energy sector, aided by government support for nuclear energy and a partnership to supply power to Microsoft’s AI infrastructure [3]. Seagate Technology also saw a nearly 30% increase, as cloud providers and AI data centers drove demand for its high-capacity storage solutions [3].

Healthcare Sector Struggles

In contrast, the healthcare sector faced significant headwinds, with UnitedHealth Group emerging as the worst-performing stock in the S&P 500 for May [1, 2]. The company’s stock plunged 26.6% following the abrupt resignation of CEO Andrew Witty and the withdrawal of its full-year earnings outlook due to surging Medicare Advantage costs [1, 3]. UnitedHealth also faced external scrutiny regarding allegations of Medicare fraud and improper bonus payments to nursing homes, claims the company has refuted [1]. Regeneron Pharmaceuticals also struggled, losing 18.2% of its value after its experimental drug, itepekimab, failed in a phase 3 trial, leading investors to anticipate a multi-year delay for the product [1].

Why it matters

The divergence in performance between energy-focused companies and healthcare giants highlights how sector-specific news can dictate market movement even during a broad index recovery [3]. For investors, the volatility in healthcare—particularly regarding Medicare Advantage utilization and clinical trial outcomes—remains a critical area of focus [1, 3]. Looking ahead, UnitedHealth’s second-quarter earnings report, scheduled for July 29, is expected to provide further clarity on the company’s path toward its goal of returning to growth in 2026 [1].