[U.S. Market Recap] Sept 28: Nasdaq Falls 0.92% as Iran Tensions Flare and Long-Term Yields Hit a 19-Year High

Hey everyone, Hirokichi here. Today I’m recapping the U.S. stock market session from Monday, September 28, 2026. The short version: all three major indexes — the Dow, the S&P 500, and the Nasdaq Composite — closed lower across the board. Rising tensions around Iran sent oil prices sharply higher, and long-term Treasury yields climbed to their highest level in 19 years, both of which weighed on stocks. On the individual-stock side, Nvidia (NVDA) rose after a huge buyback increase, while MongoDB (MDB) plunged on a sudden CEO departure. It was a day with some clear winners and losers.

All three indexes slipped, with the Nasdaq Composite down 0.92%

Let’s start with the closing levels for the three major indexes. On the previous trading day, Friday Sept 25, the Dow had bounced 478 points as oil prices eased (my Sept 25 U.S. market recap), but selling took over again as the new week began.

As the table shows, the Nasdaq Composite took the biggest hit, meaning growth and tech names bore the brunt of the selling. The small-cap-heavy Russell 2000 also fell, closing at 2,817.91 (-0.69%), so the weakness was broad-based across market caps.

The chart makes it clearer: the Nasdaq’s drop was noticeably larger than the S&P 500’s or the Dow’s, showing that selling was concentrated in growth-heavy tech names.

What drove the market: escalating Iran tensions and surging long-term yields

Two main factors drove Monday’s decline.

The first was geopolitical risk. Reports emerged that President Trump had rejected a proposal from Iran to reopen the Strait of Hormuz, and oil prices jumped in response. WTI crude rose 4.22% to $96.31 a barrel, while Brent crude gained 4.02% to $108.50 (sources: Reuters, CNBC). Higher oil prices tend to revive inflation worries, which is a headwind for stocks.

The second factor was interest rates. The 10-year Treasury yield climbed above the key 5.2% level, its highest point in roughly 19 years, since 2007. The 30-year yield also rose above 5.5%. Behind this was a stronger-than-expected Dallas Fed manufacturing index, which came in at 9.8 versus a forecast of 7.8 — a sign of economic resilience that ironically fed fears that rate cuts could be pushed further out. Since higher rates make future earnings less valuable in today’s terms, growth stocks tend to sell off more, which helps explain why the Nasdaq fell harder than the other indexes.

The VIX (a volatility index derived from S&P 500 options, often called the “fear gauge”) rose to 16.33, up 9.82% from the prior day. That’s not a historically extreme crisis level, but it does show investor caution increased noticeably.

Notable stocks: Nvidia, MongoDB, Boeing, and Roblox

Here’s a look at the stocks that moved the most on the day.

The chart shows MongoDB’s decline was by far the steepest, followed by Roblox and then Boeing, while Nvidia was the only one of the four to finish in positive territory.

Nvidia (NVDA) rose after its board approved an additional $150 billion for its share buyback program, lifting the total remaining authorization to $235 billion — reportedly the largest single buyback increase by a U.S. company on record. CEO Jensen Huang cited “attractive valuation” as the reason, signaling confidence in the company’s growth outlook in AI and accelerated computing. The stock closing up 1.68% suggests the market took the announcement as a genuine vote of confidence.

MongoDB (MDB) was the day’s biggest mover. CEO CJ Desai stepped down to take a senior role at Meta, and the stock plunged 19% to close at $335.32. The company said the departure wasn’t related to any operational issues, but a sudden change at the top clearly rattled investors. Founder Dev Ittycheria stepped in as interim president and CEO. What likely amplified the drop wasn’t the business itself, but the uncertainty of not yet having a confirmed permanent successor.

Boeing (BA) fell after the FAA announced it was delaying certification of the 737 MAX 10 due to newly identified software issues. The FAA is reportedly holding off until it can reassess whether the problems pose any flight-safety risk. Coming at a time when deliveries were expected soon, this is a real setback for a company still working through its recovery. Shares fell as much as 6.8% intraday.

Roblox (RBLX) dropped after Jefferies downgraded the stock to “Underperform” with a $38 price target, citing concerns that bookings growth would come in well below Wall Street’s expectations. Shares fell 7.84% on the news. Since Roblox had been seen as a stock with strong momentum, a downgrade right ahead of earnings triggered some disappointment-driven selling.

Worth a quick mention too: small-cap biotech Kodiak Sciences (KOD) soared an astonishing 154.56% after reporting positive Phase 3 trial results — a good reminder that single pieces of news can move small-cap stocks by multiples in a single day.

Sector and ETF moves

By sector, energy names benefited from the oil price spike, while gold and silver mining stocks were pressured by the same move. Tech and AI-related names were soft as well, partly on reports that OpenAI had paused training of an advanced model. Defense and aerospace names were weak, epitomized by Boeing’s drop, and market breadth was poor overall, with roughly twice as many decliners as advancers on the NYSE. On the flip side, space-related names (on positive analyst commentary around SpaceX), pharma and biotech (on several positive trial readouts), and insurance (Morgan Stanley upgraded Reinsurance Group of America to Overweight) held up relatively well.

A note on ETFs many of you likely hold: S&P 500 trackers like VOO and VTI likely moved in line with the index, roughly -0.7% to -0.8%, and Nasdaq-tracking QQQ likely fell around -0.9%. For high-dividend ETFs like SPYD, HDV, and VYM, I wasn’t able to confirm exact closing figures or percentage moves in today’s research. Given that a sharp rise in long-term yields tends to be a headwind for dividend-focused names, these may have fallen by a similar amount or more, but I can’t state that with certainty — please check your own brokerage account for the precise numbers.

What to watch in Japanese stocks today

Given the U.S. market’s decline, Japanese stocks are likely to face similar pressure today. Here are three points worth watching:

(1) Long-term rates: With U.S. long-term yields at a 19-year high, growth and high-multiple stocks in Japan may continue to face headwinds too.

(2) Ripple effects from higher oil: Rising crude prices are a tailwind for resource and energy names, but can also weigh on other sectors through higher transport and material costs.

(3) Further news on Iran: Geopolitical risk can shift quickly. Whether upcoming reports point toward negotiation progress or further escalation could swing both oil prices and equities.

One note on this article: a few figures (specifically, closing values for the high-dividend ETFs mentioned above) couldn’t be confirmed in today’s research and were left blank rather than guessed. Please check your brokerage’s own data for the most accurate current numbers.

Let’s keep at it, slow and steady. Have a good day!

日本語版はこちら → 【米国株まとめ】9月28日はナスダックが0.92%反落！

* This article is for informational purposes only and does not recommend any specific investment. Please make investment decisions at your own responsibility.

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