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Key Takeaways

• The S&P 500 eked out a gain of 0.1% on Monday, May 19, 2025, as investors weighed the implications of Moody's downgrading its U.S. credit rating.
  

• UnitedHealth shares extended their recovery as a filing showed the insurer's incoming CEO purchasing a significant amount of shares.

• Shares of solar firms and other renewable energy companies fell as Congressional leaders discussed an accelerated phase-out of certain clean energy tax credits.

Major U.S. equities indexes ticked higher to kick off the trading week, bolstered by outperformance in biotech and the health care sectors even as investors digested the downgraded view on U.S. government creditworthiness from ratings agency Moody's.

After trading in negative territory for much of the day, the S&P 500 gained strength in the afternoon to end 0.1% higher. The Dow was up 0.3%, while the Nasdaq managed a slender gain above last week's closing level. Read Investopedia's full coverage of the day's trading here.

UnitedHealth Group (UNH) stock jumped 8.2%, marking the top daily performance in the S&P 500. While Monday's move higher extended a recovery that began late last week, shares of the insurance giant had been under heavy pressure after reports of a Justice Department investigation into possible Medicare fraud compounded news about the departure of UnitedHealth's top executive and suspension of its guidance. As the stock rebounded, filings showed that incoming CEO Stephen Hemsley purchased a significant stake in the company.

The Food and Drug Administration granted full approval for the protein-based COVID-19 vaccine produced by Novavax (NVAX), and shares of the biotech firm surged 15%. Shares of fellow vaccine maker Moderna (MRNA) were up 6.2%.

Dollar General (DG) shares advanced 4.9%, adding to gains posted at the end of last week after Walmart (WMT) discussed tariff-related price increases on its earnings call. Analysts have highlighted that Dollar General has limited tariff exposure compared with some of its rivals in discount retail.

Shares of several solar energy companies moved lower after Republican leaders in the House reportedly committed to eliminating certain clean energy tax credits earlier than anticipated. An initial budget proposal from the House Ways and Means Committee released last week included plans to roll back many provisions of the Inflation Reduction Act, including tax credits for residential solar installations. Shares of panel manufacturer First Solar (FSLR) sank 7.6%, losing the most of any S&P 500 stock, while shares of solar equipment maker Enphase Energy (ENPH) lost 3.2%.