September 18 U.S. Stock Market Outlook: Falling Oil Prices Provide Support, but Triple Witching Volatility Bears Watching
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Ahead of the opening bell on September 18, falling oil prices and the previous day's technology stock rebound provide a favorable backdrop for U.S. equities. However, the Federal Reserve raised its benchmark interest rate by 0.25% points two days earlier, and the day is a triple witching session, when stock index futures, stock index options, and individual stock options expire simultaneously. As a result, intraday movements could differ from the market's opening direction.
The reference time is 2026-09-18 at 5:28 p.m. Korea Standard Time. Since the regular New York trading session has not yet begun, the direction of the day's closing prices cannot be determined.
What Matters Most for U.S. Stocks Today?
The first variables to watch are international oil prices and U.S. Treasury yields.
On the previous day, September 17, the S&P 500 rose 1.14%, the Nasdaq gained 1.69%, and the Dow Jones Industrial Average advanced 0.62%. Technology stocks led the rebound as international oil prices and U.S. Treasury yields declined.
Oil prices continued to fall during Asian trading hours on September 18. Brent crude dropped as low as 103.29 dollars per barrel during the session, while the yield on the 10-year U.S. Treasury reached approximately 4.936%.
Therefore, rather than focusing solely on the fact that the Fed raised interest rates, whether oil prices and long-term Treasury yields begin rising again could be a more important factor in assessing the U.S. stock market's short-term direction.
The Fed Raised Interest Rates to 3.75–4.00%
At its September 16 meeting, the Federal Open Market Committee (FOMC) raised the target range for the federal funds rate by 0.25% points to 3.75–4.00%.
The vote was 12 to 0.
The Fed assessed that U.S. economic activity continued to expand at a solid pace, with domestic spending and capital investment also remaining robust. At the same time, it stated that inflation remained elevated.
Therefore, even if stocks open higher on September 18, it would be difficult to conclude that interest-rate pressures have disappeared. If oil prices and Treasury yields rise again, the pressure that higher discount rates place on growth and technology stocks could return to the forefront.
The Nasdaq Led the Previous Day's Rebound
Based on closing prices on September 17, the Nasdaq's 1.69% gain exceeded the S&P 500's 1.14% increase by 0.55% points. It was also 1.07% points higher than the Dow's 0.62% gain.
These are the author's calculations, based on the Nasdaq at 1.69%, the S&P 500 at 1.14%, and the Dow at 0.62%.
Because technology stocks led the previous day's rebound, it is also important to monitor the Nasdaq, semiconductor stocks, and major technology companies on 18.
However, there is no basis for assuming that sectors posting strong gains one day will continue moving in the same direction during the next trading session. Particularly in the current environment, where interest rates and oil prices are moving rapidly, the previous day's gains alone are insufficient to predict the day's market direction.
September 18 Is a Triple Witching Day
September 18 is designated as a triple witching date in the New York Stock Exchange's 2026 trading calendar.
The NYSE calendar lists the 2026 triple witching dates as March 20, June 18, September 18, and December 18. On September 18, the final trading sessions for expiring stock index futures, stock index options, and individual stock options coincide.
Regular rebalancing of the S&P 400, 500, and 600 indices is also scheduled for the same day.
For this reason, it is advisable to monitor trading volume and changes in supply and demand toward the end of the session, rather than focusing solely on the direction of the indices. When expiration-related trading becomes concentrated, intraday price movements may not provide a reliable indication of the market's medium-term direction.
The U.S. Leading Economic Index Will Also Be Released at 11 p.m.
The U.S. Leading Economic Index (LEI) for August is scheduled for release at 11 p.m. Korea Standard Time on September 18. The scheduled release time is 10 a.m. U.S. Eastern Time.
The previous U.S. Leading Economic Index for July rose 0.2% from the preceding month to 99.5. The 6-month change from 1 to July also turned positive, recording an increase of 0.2%.
The August figure had not yet been released at the time this article was checked. Therefore, forecasts cannot be presented as actual results. Once the data is released, it will be necessary to determine whether the improvement seen in July has continued.
Key Figures to Watch Throughout Today's Trading Session
Before the opening bell, international oil prices and the yield on the 10-year U.S. Treasury are worth checking first.
Once regular trading begins, investors should monitor not only the direction of the Nasdaq and S&P 500 but also whether technology stocks can hold on to the previous day's gains. The U.S. Leading Economic Index for August is then scheduled for release at 11 p.m. Korea Standard Time.
Finally, toward the end of the session, it will be important to distinguish changes in trading volume associated with triple witching from those related to index rebalancing.
Based on the factors confirmed so far, falling oil prices have helped ease pressure on the stock market since the previous day. On the other hand, monetary policy uncertainty following the Fed's 0.25%-point rate increase and supply-and-demand pressures associated with triple witching remain.
Therefore, rather than predicting a specific direction for U.S. stocks on September 18, the approach most consistent with currently available information is to monitor the following factors in sequence: whether oil prices continue falling → the 10-year U.S. Treasury yield → technology stock performance → the Leading Economic Index release at 11 p.m. → expiration-related trading flows toward the end of the session.
Stock markets can move rapidly in response to geopolitical developments and changes in interest rates and oil prices. The information above does not guarantee that any particular stock or index will rise or fall, nor does it guarantee investment returns.
※ This article is provided for informational purposes to help readers understand market trends and does not constitute an investment recommendation concerning any particular stock or asset. All final investment decisions and their associated responsibilities rest with the individual investor.
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이 포스팅은 쿠팡 파트너스 활동의 일환으로, 이에 따른 일정액의 수수료를 제공받습니다.