S&P 500 lost 0.35% in September while nine of 11 sectors fell

The S&P 500 ended September 2026 down 0.35%. That is the number most people will have seen, and on its own it describes a dull month. It is also the least representative figure in the whole release. Of the 11 sectors that make up the index, nine fell. The S&P 500 Equal Weight index, which holds the same 500 companies but gives each the same weight, fell 4.81%. The S&P SmallCap 600 fell 5.57%. The Dow Jones Industrial Average fell 4.29%. The near-flat headline was produced by two sectors, Information Technology and Communication Services, each up a little over 4%.

Every figure in this piece comes from two documents S&P Dow Jones Indices publishes at each month-end, the Index Dashboard: U.S. and the Index Dashboard: U.S. Sector, both carrying data as of September 30, 2026, plus one S&P DJI press release dated September 4, 2026. Returns are total returns, which include dividends. We do not print index closing levels; S&P DJI licenses those, and the percentages tell the story.

September: a flat index built from falling parts

The mechanism is weighting. The S&P 500 weights each company by its float-adjusted market capitalisation, so the largest technology and communication companies account for a large share of the index. When those sectors rise 4% and the other nine fall, the index lands near zero. The equal-weight version removes that effect, and its −4.81% is a fairer description of what the typical S&P 500 member did. S&P DJI's own factor table makes the same point from another angle: the S&P 500 Top 50, the fifty largest members, rose 1.90% in September, and the S&P 500 Growth index rose 1.95%, while S&P 500 Value fell 3.10%.

That pattern, with the defensive and income-oriented indices falling hardest, is consistent with a month in which the 10-year Treasury yield reached 5.00% on September 15, 2026 and the Federal Reserve raised its target range to 3.75%–4.00% on September 16. Higher bond yields compete directly with dividend yields, and the sectors that behave most like bonds, Utilities and Real Estate, were both down about 6%. The site's pieces on the 10-year at 5% and the unanimous September hike set out those two events.

The third quarter: up 2.30%, carried by Energy and Technology

In a reversal from the trends observed in Q2, mega-caps outperformed, with the S&P 500 Top 50 up 4% in Q3. Mid and small caps underperformed large caps, with the S&P MidCap 400 and S&P SmallCap 600 down 6% and 8%, respectively.S&P Dow Jones Indices, Index Dashboard: U.S., commentary, data as of September 30, 2026

S&P DJI's own description of the quarter is short. It attributes the Energy gain to rising crude oil and the Utilities loss to rates.

Thanks to the tailwind of rising crude oil prices, Energy led with a 17% gain. Rate-sensitive Utilities were the laggard, down 12%.S&P Dow Jones Indices, Index Dashboard: U.S., commentary, data as of September 30, 2026

The oil side of that is covered in oil at $107. Energy was positive in Q3 at every size tier: the U.S. Sector dashboard gives the Energy Select Sector up 16.27% for the quarter, the MidCap 400 Energy sector up 6.28% and the SmallCap 600 Energy sector up 5.50%, and its commentary states that Energy was the only sector to generate positive returns across all cap tiers. Energy nonetheless fell 2.72% in September after leading the quarter, so the ranking depends on which period you look at.

Why the headline and the average member can disagree so much

Three things happened at once in September, and each widened the gap between the index and its typical constituent.

• Concentration. The two rising sectors are where the largest companies sit. The S&P 500 Top 50 rose 1.90% while the equal-weight index fell 4.81%, a 6.71-point gap in one month between the biggest fifty and the average member of the same index.
• Rates. With the 10-year Treasury at 5.00% on September 15, 2026, the sectors and strategies that pay the highest dividends, Utilities, Real Estate, Low Volatility High Dividend, fell the most. The S&P DJI sector dashboard lists Real Estate's dividend yield at 3.2% and Utilities at 2.8%, against 0.5% for Technology; the lower the yield, the less the comparison with a 5% bond bites.
• Size. Smaller companies fell more than large ones in both the month and the quarter: SmallCap 600 −5.57% and MidCap 400 −4.22% in September, against −0.35% for the 500. S&P DJI's commentary does not give a reason, and we do not supply one.

What changed inside the index on September 21

What it means for your money

The arithmetic is simple once the figures are in front of you. Take $10,000 held through September 2026 in a fund tracking each index, before fees and taxes, and ignoring tracking error.

Two practical points follow, neither of which is advice. First, the name of the fund matters more than the phrase “U.S. stocks”: a cap-weighted S&P 500 fund, an equal-weight fund, a dividend fund and a small-cap fund had four different Septembers. The site's diversification and ETF explainers set out how to check what an index fund actually holds. Second, a 0.35% monthly move is well inside the ordinary range for the index; the Market Memory pages show how unusual any given day or month has been against the historical record, and the loss-recovery tool shows the gain needed to recover a given fall, which for −7.93% is larger than 7.93%.

For anyone measuring their own portfolio against “the market”, the dashboard is also a caution about the benchmark. A portfolio with mid caps, small caps and dividend stocks in it would have trailed the S&P 500 by several points in September without anything going wrong. The Russell 2000 record and S&P slip piece from earlier in 2026 shows the ranking of large and small has flipped before.