DB CotD Groundhog Month Sept 15

Global Cross-Discipline Date 15 September 2026 Thematic Research

DB CoTD: Groundhog Month Jim Reid Whether it’s AI doomerism or the prospect of a renewed energy shock, September Global Head of Macro and Thematic Research 2026 is increasingly following its well-established seasonal script.

Henry Allen Today’s CoTD comes from my pack last week “The Home Straight” (link here) and Macro Strategist shows that, regardless of the time horizon examined — the last 100 years, 50 years, years, 10 years or even just the last five years — September has consistently been the weakest month of the year for markets. Midterm years appear to be even weaker Raj Bhattacharyya Research Associate than average.

There is no obvious explanation for this pattern, with lots of spurious ones. Perhaps it has become partly self-fulfilling, but the consistency of the trend makes it difficult to dismiss.

That said, October and November are seasonally strong months, particularly in midterm years, as the chart highlights.

This is why it is always difficult to interpret market weakness at this time of year. In reality, much of the recent softness across global markets appears to be more energy-related than either seasonally driven or even AI-related. As a result, markets are likely to remain heavily influenced by the direction of energy prices. Ahead of the midterms, the US administration will probably be reluctant to see the situation deteriorate further, although there are actors on the other side of the Middle East conflict who may seek to exploit that constraint.

Taken together, it makes for a complicated backdrop heading into the midterms, overlaid on an already challenging seasonal period. But are the prospects of a seasonal rebound ahead enough to prevent too many shorts or profit-takers now?

We have three new pieces on the Deutsche Bank Research Institute (DBRI) overnight. 1) A piece from Adrian Cox here on the latest AI doomerism, and framing it in terms of bad tech predictions in the past; 2) A piece here from Henry Allen on the implications of the world moving to a supply-driven world, and 3) A piece from Miha Hribernik here previewing the Trump-Xi summit on September 24th. There's lots more new research on the site from September so far. So while it might be a seasonally soft month for markets, its proving to be a productive month for the DBRI!

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15 September 2026 Thematic Research

Figure 1: S&P 500 Monthly Performance (1928-2025). Seasonals consistently matter.

March Since 1928 April Past 20 Years Past 10 Years May Midterm Election Years June

August September has the worst track September record of the entire year

Source : Bloomberg Finance LP, Deutsche Bank