As of September 21, 2026
S&P 500: Why Isn’t It Collapsing? Tracking the ‘Anomalies’ in the U.S. Market
Looking at the U.S. stock market, there is a somewhat strange movement in the current S&P 500.
In the U.S., vigilance against inflation continues, and the 10-year U.S. Treasury yield has risen to a level exceeding 5%.
Furthermore, crude oil prices are hovering above $100, and the Fed implemented a rate hike at its September meeting. Concerns about additional rate hikes remain for the future.
Even so, the S&P 500 has not collapsed significantly.
Rather, it is maintaining a high range while experiencing short-term adjustments.
Why is this?
This time, we will focus on the S&P 500 itself and track what is happening in the current U.S. market.
■ The Current Position of the S&P 500
The closing price of the S&P 500 on September 18, 2026, was 7,650.50.
On this day, the S&P 500 rose 0.17% from the previous day.
It was mostly flat for the week, but the NASDAQ rose 0.40%.
On the other hand, the 10-year U.S. Treasury yield has risen to a level exceeding 5%, so looking only at the interest rate environment, it is by no means an easy situation for the stock market.
Even so, the S&P 500 is maintaining the 7,600 level.
■ It Returns Even After Starting to Collapse
This is the point of this article.
The S&P 500 fell significantly on September 16 due to the Fed’s rate hike and concerns about inflation.
However, it rebounded the following day, the 17th.
It also ended the week with a slight gain on the 18th.
According to Reuters’ technical analysis, although the S&P 500 temporarily fell below the 50-day moving average during the decline on September 16, it subsequently recovered.
The 7,677.02 level reached on September 11 is being watched as an important point of resistance.
On the other hand, the area around 7,617 is considered an important level on the downside.
In other words, the current S&P 500 is neither
a market that easily collapses due to rising interest rates
nor
a market that rises in a straight line.
It is in a state of searching for its next direction while digesting information in a high-price range.
■ Why Are Stocks Bought Even When Interest Rates Are High?
Usually, if the 10-year U.S. Treasury yield rises, it becomes a headwind for the stock market.
Growth stocks, in particular, which have priced in future profit growth, tend to have their corporate value evaluations scrutinized more strictly due to rising interest rates.
However, there is another force at work right now.
That is AI-related investment.
Investments in AI, semiconductors, data centers, etc., are continuing, and expectations for corporate growth are supporting the market.
On September 21, AI-related stocks also rose in U.S. stock futures.
Intel, Marvell, Meta, Dell, and Accenture were bought, and S&P 500 futures also rose.
In other words, in the current market,
pressure on stock prices due to rising interest rates
and
expectations for AI and corporate growth
exist simultaneously.
■ Crude Oil Prices Are Also an Important Factor for the S&P 500
Another thing that cannot be ignored is crude oil.
When crude oil prices rise, it leads to concerns about rising corporate costs and a resurgence of inflation.
If inflation is prolonged, the possibility that the Fed will maintain interest rates at a high level also increases.
Therefore, a flow is created:
Rising crude oil
↓
Inflation concerns
↓
Rising interest rates
↓
Pressure on stock prices.
In fact, in mid-September, there was a scene where the S&P 500 fell due to the combination of high crude oil prices and rising U.S. Treasury yields.
However, on September 21, crude oil prices fell.
According to Reuters, the decline in crude oil prices led to a drop in bond yields, which, along with the rise in AI-related stocks, pushed up U.S. stock futures.
In other words, to think about why the S&P 500 does not collapse, looking only at the index is not enough.
It is necessary to look at the movements of crude oil and interest rates at the same time.
■ Large-Cap Stocks Supporting the S&P 500
The S&P 500 is an index centered on large U.S. companies.
Therefore, when looking at the index as a whole, the movements of companies with large market capitalizations among the constituent stocks become important.
If large companies related to current growth themes such as AI, semiconductors, cloud, and data centers are bought, it becomes a force that supports the entire index.
On the other hand, if these large-cap stocks are sold off all at once, the impact on the S&P 500 will also be significant.
That is precisely why,
instead of just looking at the result that ‘the S&P 500 is strong’,
it is necessary to look at ‘what is supporting the S&P 500’.
■ Looking at the Differences with the NASDAQ Reveals More
The S&P 500 and the NASDAQ seem similar, but their roles are different.
The S&P 500 is a representative index for looking at the state of the entire U.S. large-cap stock market.
The NASDAQ is a market that is more strongly influenced by technology and growth companies.
On September 18, while the S&P 500 rose 0.17%, the NASDAQ rose 0.40%.
This is one piece of evidence showing that while there is vigilance against rising interest rates, funds remain in growth sectors such as AI and semiconductors.
■ Even So, You Cannot Let Your Guard Down
This is important.
Just because the S&P 500 has not collapsed does not mean that the risk has disappeared.
According to Reuters’ analysis, if it falls below the 7,617 level, 7,520 and then 7,507.7 are being watched as the next important downside levels.
If the decline continues further, an adjustment risk of about 6–8% is also assumed.
Conversely, if it clearly exceeds the 7,677.02 level of September 11, the 7,756–7,772 area is watched as the next upside zone.
In other words, for the current S&P 500,
‘not having collapsed’
and
‘having no risk’
are completely different things.
■ September 21, 2026: The Meaning of Looking at the S&P 500
In the current U.S. market,
S&P 500
AI/Semiconductors
10-year U.S. Treasury
Crude oil
Fed
Inflation
these are complexly connected.
If interest rates rise, there is pressure on stock prices.
If crude oil rises, vigilance against inflation intensifies.
Even so, if expectations for AI-related investment and corporate growth are strong, funds remain in the stock market.
The result of this tug-of-war is reflected in the current S&P 500.
Therefore, this ‘anomaly’ does not mean that the S&P 500 is simply strong.
It is the fact that the index is maintaining a high-price range despite the accumulation of negative factors.
That is where the characteristics of the current U.S. market lie.
■ Points to Watch From Now On
What is important when looking at the S&P 500 in the future is:
① Can it exceed 7,677.02?
② Can it maintain the 7,617 level?
③ How will the 10-year U.S. Treasury yield move around 5%?
④ How will crude oil prices move at levels exceeding $100?
⑤ Can AI/semiconductor stocks continue to support the market?
⑥ How will the Fed judge additional rate hikes?
These are the 6 points.
When thinking about which way the S&P 500 will move next, it is necessary to look not only at the index but also at the interest rates, crude oil, AI, and corporate earnings behind it together.
■ As U.S. Market Lab
Until now, at U.S. Market Lab, we have focused on individual stocks such as low-priced stocks, growth stocks, AI, semiconductors, and energy.
However, before looking at individual stocks,
it is also important to confirm ‘where the entire U.S. market is in the first place’.
At the center of that is the S&P 500.
If the S&P 500 is strong, there is a possibility that a tailwind will be created for the inflow of funds into individual stocks.
Conversely, if the S&P 500 breaks important support levels, there is a possibility that the impact of the entire market will reach individual stocks as well.
That is precisely why, from now on at U.S. Market Lab, we will track not only individual stocks but also the movements of the entire U.S. market, including the S&P 500.
As of September 21, 2026, the S&P 500 has not yet collapsed.
However, what you really should look at is not just the result that it ‘does not collapse’.
Why doesn’t it collapse?
What is supporting it?
And what will happen when that support collapses?
By tracking up to that point, the current position of the U.S. market becomes visible.
This article was created based on information available as of September 21, 2026.
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