Meta's 11% jump added $194 billion to the S&P 500. Four stocks supplied 45% of the day's gain.

Meta added $193.7 billion to the S&P 500's market value on Monday, its biggest one-day dollar gain in our data and 18.3% of the index's entire $1.06 trillion rise. It did that from a starting weight of 2.4% of the index.

$META closed up 11.43% at $741.25. Alongside it, $NVDA, $AMD and $INTC put on another $284.0 billion between them. Those four stocks were 12.2% of the S&P 500's value at Friday's close and supplied 45.1% of Monday's gain. The published S&P 500 finished up 1.49% at 7,764.70; our own cap-weighted sum of the 500 constituents gives 1.51%, and every figure below comes from that sum.

Four stocks, 45% of the gain

The ten biggest dollar gainers added $770.3 billion, 72.8% of the total. Take Meta out and the index rose 1.27% instead of 1.51%.

Meta's day in context

Since our snapshots begin on 15 June, Meta's previous best one-day move was +8.81% on 2 July, worth $126.0 billion. Monday beat that on both counts. It also came right after a down day: Meta fell 2.43% on Friday 18 September.

Reports on the day pointed to two things. Wells Fargo analyst Ken Gawrelski raised his price target on Meta to $796 from $640, and Meta's new Muse AI assistant reached the top of Apple's U.S. App Store, according to The Motley Fool and TipRanks. The Fool put volume at 48.7 million shares, about 157% above the three-month average. Meta Connect, the company's annual conference, starts Wednesday. We can measure the size of the move; we cannot say how much of it any one of those items explains.

Where it sits on the map

Technology rose 3.03% cap-weighted, adding $844.5 billion, or 79.8% of the index's gain, and 66 of its 77 stocks closed higher. One caveat about our own data: it files Meta under Technology rather than Communication Services. Without Meta, the sector still rose 2.48% and added $650.8 billion. Either way it was the fourth-largest Technology day in our data by both percentage and dollars, behind 31 July (+5.23%), 5 August (+4.12%) and 16 June (+3.38%).

Chips were part of the same session. Yahoo Finance's market blog reported the Nasdaq Composite closing at a record after a 2.26% gain, with AMD passing a $1 trillion market value. In our data AMD's value ended the day at $1.005 trillion.

The other side of the map

Energy was the S&P 500's weakest sector, down 2.55% and $60.3 billion, with 16 of its 21 stocks lower. $XOM fell 3.20% and $CVX fell 2.79%, together $33.0 billion. Yahoo Finance reported that Brent and WTI crude both fell below $100 a barrel on hopes of U.S.-Iran talks. Refiners fell hardest: $MPC lost 5.30% and $VLO 4.84%.

It is the second time in six sessions that Energy has fallen more than 2.5%: it lost 3.03% on 16 September. Those two days rank second and third among the worst Energy sessions in our data, behind 16 June (-3.54%).

A strong day that was not equally strong everywhere

The average stock in the index rose 0.55%; the median stock rose 0.30%. There were 289 gainers and 210 decliners, and the decliners together lost $185.2 billion, so the gap between the headline and the typical stock was wide. That is not unusual for a big up day in this dataset. There have been five sessions since June with a cap-weighted gain of 1.5% or more, and the share of each carried by its single biggest contributor varied a lot:

Monday's 210 decliners were more than on 4 and 5 August but fewer than on 16 June or 31 July, and Meta's share of the gain was the third-largest of the five, behind $MSFT on 31 July and $GOOGL on 4 August.

What this does not tell you

It is one session. Nothing here says whether Meta, or the four-stock group, holds the move, and a market-value change is not a verdict on what a company is worth. What the map does show is how much of a 1.5% index gain can rest on a handful of names, and that a day of record highs in the Nasdaq also had 210 S&P 500 decliners and a sector, Energy, that lost more than $60 billion.