Midterm election years tend to follow a script on Wall Street, and investors are watching closely as the calendar moves into the stretch that history says usually delivers the strongest returns of the year.

September's rough patch, right on schedule

The pattern typically starts with a slump. September has historically been the weakest month of the year in midterm cycles, averaging a 0.8 percent decline for the S&P 500. UBS strategist Maxwell Grinacoff has described the market as typically choppy from late August into early October, with a median decline of about 1.4 percent over that stretch, a rough patch that has shown up more or less on schedule again this year.

Then October usually takes over

Ryan Detrick, chief market strategist at Carson Group, has tracked 19 midterm election years dating back to 1950 and found the S&P 500 posts an average gain of 3.0 percent in October during those years, the largest average monthly return of the year, which is why he calls it the best month of the year in a midterm cycle. Stocks finished October positive in 73.7 percent of those 19 years.

November wins more often, even if it gains less

The seasonal pattern has a wrinkle worth noting. November actually posts a positive return more frequently than October, finishing higher in 78.9 percent of midterm years, even though its average gain of 2.7 percent runs slightly smaller. October tends to deliver the bigger single move, in other words, while November is the more reliably positive month, a distinction that matters for anyone trying to time an entry rather than simply betting on a strong fourth quarter overall.

A stretch that rarely disappoints

Zoomed out further, the pattern holds up well. J.P. Morgan Asset Management has found the S&P 500 averages a 6.6 percent gain across the full fourth quarter in midterm years, and Detrick's data shows the period from September through year end averaging a 6 percent return in midterm years compared with 4 percent in other years. Since 1950, only three of the 19 midterm cycles broke the pattern with losses over that stretch, in 1978 amid high inflation, in 2002 as the tech bubble finished unwinding, and in 2018 amid a trade war and a Federal Reserve still raising interest rates.

The S&P 500 entered this year's stretch already up about 13 percent for 2026 as of September 18, meaning even an average midterm year seasonal pattern would add meaningfully more to what has already been a strong year for stocks.

A pattern that has held for nineteen election cycles is not a guarantee. It is simply the way the odds have leaned every time investors have bet against it.

Strategists are careful to note that seasonality is a tendency built from a small number of historical cycles, not a rule. Still, with markets historically beginning to rally less than a month before Election Day, the coming weeks will offer an early read on whether 2026 sticks to the script or joins the short list of years that broke it.