S&P 500 and Nasdaq hit worst week since June

U.S. stocks ended sharply lower Oct. 16, 2026, MarketWatch reported. The S&P 500, an index of 500 large U.S. firms, and the Nasdaq Composite, weighted toward tech stocks, both had their worst week since June. For 401(k) savers — retirement accounts tied to markets — that means smaller balances.