#oil prices

If you have checked a retirement account recently, it may feel as though something changed abruptly.

That impression is real, although the timeline is slightly deceptive. August 2026 was actually a strong month for American stocks: according to Nasdaq's August market review, the S&P 500 rose 2.7 percent and the Nasdaq-100 gained 4.2 percent, their strongest August performances since 2021.

Even after September's turbulence, the broader picture is not one of a market in collapse. As of September 18, the S&P 500 remained more than 11 percent higher for 2026 and only about 2 percent below the record high it reached in mid-August.

What changed was the atmosphere.

Several forces that had been simmering in the background began reinforcing one another: oil prices climbed, inflation worries returned, Treasury yields rose, the Federal Reserve increased interest rates, and investors became less comfortable paying high prices for future corporate growth.

September 2026 at a glance

S&P 500: still more than 11% higher in 2026, but roughly 2% below its August record
August S&P 500 return: +2.7%
August Nasdaq-100 return: +4.2%
Brent crude: roughly \$100–\$110 per barrel during September's surge
10-year U.S. Treasury yield: around 5%
Federal funds target: 3.75–4.00% after the September 16 rate increase
August CPI inflation: 3.4% year over year
Federal Reserve 2026 PCE inflation projection: 3.7%

Taken together, these numbers tell much of the story: the stock market itself is still relatively strong, but the economic environment surrounding it has become noticeably less forgiving.