US stock market adds $675B at open, driven by S&P 500 rally

The US stock market did not ease into Monday morning. The S&P 500 added $675 billion in market capitalization at the open on July 27, 2026, a single-session move that signals just how quickly sentiment can shift when geopolitical clouds start to clear. The catalyst was a meaningful de-escalation between the US and Iran, which took pressure off oil markets and gave equity traders exactly the excuse they needed to buy. What actually happened Futures pointed to the move before markets even opened. The Nasdaq-100 was up 1.61% in pre-market trading, the S&P 500 gained 0.96%, and the Dow added 0.95%. To put the $675 billion figure in context, previous notable single-session market-cap moves in 2026 included a $560 billion gain on a 0.83% open and a $420 billion move on a 0.7% session. Monday’s number was the largest of those three. The S&P 500 has been trading between 7,500 and 7,600 in mid-to-late July 2026. The index posted 23 all-time highs through June alone, capping a second quarter that delivered a 15.2% gain. The week that follows matters more Monday’s open was a warm-up act. The real event is a week stacked with earnings from Microsoft, Meta, Amazon, and Apple, four c...