Apple lost $131 billion on the day BofA flagged Meta's Muse. The whole S&P 500 lost $117 billion.

$AAPL fell 2.66% on Tuesday, 29 September, and took $131.3 billion of market value with it. The S&P 500 as a whole lost $117.3 billion on the day, a 0.17% decline. One company lost more than the index did.

Put the other way round: take Apple off the map and the remaining 499 stocks finished the session up a net $14.0 billion. The index's down day was, in dollar terms, an Apple day.

The day the headline landed

The move came on the day Bank of America published a note on Apple and Meta's AI agent, Muse. As reported by GuruFocus and 24/7 Wall St., the bank warned that agents like Muse could pull online shopping activity away from Apple's ecosystem, and that Apple could keep control of device sales while losing part of the activity around product discovery, referrals and transactions. The note said Apple's updated Siri currently lacks some of Muse's background-task capabilities and broader third-party actions. BofA kept its Buy rating on Apple.

It was not the only Apple headline of the session — Yahoo Finance also ran a story tying the stock's decline to local AI moving onto desktops. Several things were in the air; the map records only what the price did.

How unusual the move was

Apple closed at $329.40. In the site's daily price history, the last time $AAPL fell further in a single session was 31 July, when it dropped 7.35%. Tuesday was its worst day in two months.

It also came on top of a 0.78% slide on Monday. Across the two sessions, Apple has given up roughly $170 billion of market value — $38.8 billion on Monday and $131.3 billion on Tuesday.

That size is what turns a 2.66% move into an index event. At $4.81 trillion, Apple was 6.9% of the S&P 500's total market cap at Tuesday's close. On its own it took about 0.19 percentage points off the index, which finished down 0.17%.

Bigger than the next four combined

Apple's loss was not just the largest on the map; it was larger than the next four biggest dollar losses put together.

Those four together lost $95.8 billion — about three-quarters of what Apple lost alone.

Meta, on the other side

$META rose 3.24% to $738.79, adding $59.0 billion — the largest dollar gain in the index. Apple's loss was a little over twice that.

Meta's gain followed two down sessions: it fell 3.33% on Friday, 25 September, and 4.79% on Monday. Tuesday's close was still below both Friday's $751.66 and the $777.59 it closed at on 24 September.

The companies named in the coverage as Muse's commerce partners barely moved. $EXPE rose 0.79% and $PYPL fell 0.72%, each a change of about $0.3 billion. $AMZN, which the reports said has blocked the agent, rose 0.21%. $MSFT was flat, down 0.05%.

Technology was split almost exactly in half

On the sector view, Technology finished essentially flat — down 0.02%, a net $6.5 billion — and 39 of its 77 members rose while 37 fell. That flat line hides two large, opposing blocks.

Without Apple, the rest of the sector added a net $124.8 billion. Much of that came from chip-equipment and chip names:

The three equipment makers alone — Applied Materials, Lam Research and KLA — added $41.4 billion, about a third of what Apple lost. $NVDA went the other way, down 0.72%.

The rest of the map

Breadth was weaker than the dollar total suggests: 296 S&P 500 stocks fell and 198 rose. Energy was the weakest sector, down 0.90% with only 1 of its 21 members higher. Utilities was the strongest, up 1.15%, with 30 of 31 rising.

Two of the day's largest percentage moves came from companies that made their own news. $FICO fell 26.64%, the worst move in the index, on the day Fannie Mae and Freddie Mac opened mortgage scoring to its rival VantageScore. $CCL rose 13.41%, the best, on the day Carnival reported record quarterly revenue.

But neither of those moved the total much: Fair Isaac's fall cost $4.8 billion. On the treemap, the day's shape was set by one tile, and it was Apple's.

This post describes market data and reported news. It is not investment advice.