The S&P 500 Enters Q4 Up 11.8% for the Year. Here's What Happened the Last 21 Times It Was Up 10-20% Through September

Correction (November 1, 2026): An earlier version of this article said the S&P 500 closed September 2026 at 7,690.96, up roughly 14.6% for the year, citing index data compiled by Trading Economics. The index closed at 7,651.54 on September 30, 2026 against a 2025 year-end close of 6,845.50 -- a gain of 11.8%. The figure and its attribution have been corrected to the S&P 500 daily close series published by S&P Dow Jones Indices and distributed by FRED. 2026 still falls inside the 10%-20% band this article studies, but in the lower part of it rather than the middle.

The S&P 500 closed out September 2026 at 7,651.54, up roughly 11.8% for the year, according to the S&P 500 daily close series published by S&P Dow Jones Indices and distributed by FRED, as of September 30, 2026. That figure matters less on its own than what it sets up: the index is entering the fourth quarter, historically the strongest quarter of the year, already up double digits. That is not a new situation. Since 1950, the S&P 500 has entered October with a year-to-date gain between 10% and 20% twenty-one separate times. This piece lays out what happened in those 21 prior cases, where 2026 sits inside that distribution, and the two specific years -- one infamous, one recent -- where the pattern broke.

New York Stock Exchange building, seen from Federal Hall. Reference photo taken October 23, 2008; not an image of the trading session discussed here. Photo: Andy C, Wikimedia Commons, CC BY-SA 3.0. Uncropped.

Key takeaways

• The S&P 500 closed September 30, 2026 at 7,651.54, up 11.8% for the year on a price basis -- inside the 10%-20% year-to-date band this article studies, toward its lower end.
• Since 1950 the index has entered October inside that band 21 times. It finished the fourth quarter higher in 18 of them, an 85.7% hit rate, with an average Q4 gain of 5.3%.
• Across all years since 1950 the Q4 hit rate is 80.3% with an average gain of 4.2%, so this setup has historically been better than an average year, not worse.
• The two cases this article studies as the tail: the S&P 500 fell 20.47% in the single session of October 19, 1987, and 14.0% across the fourth quarter of 2018.

Figures checked: September 30, 2026 (index close re-verified against FRED on November 1, 2026).

The setup: up double digits, heading into the best quarter of the year

Fourth-quarter seasonality is one of the more durable patterns in U.S. equity history. Carson Group's chief market strategist, Ryan Detrick, has tracked S&P 500 returns since 1950 and finds that the index has posted a positive fourth quarter 80.3% of the time across all years, averaging a 4.2% gain. That is already the best of the four quarters on both counts. But 2026 is not an average year going into Q4 -- it is a year that has already rallied hard, and that changes the reference class that actually applies.

Narrowing to the actual setup: 10%-20% YTD through September

Detrick's research narrows the sample specifically to years where the S&P 500 was up between 10% and 20% for the year through the end of the third quarter -- the band 2026 falls into at 11.8%. Since 1950, that exact setup has occurred 21 times. The index finished the fourth quarter higher in 18 of those 21 years, an 85.7% hit rate, with an average Q4 gain of 5.3% -- above the all-year average of 4.2%. Separately, looking only at the most recent 13 years regardless of the September setup, the S&P 500 finished Q4 positive in 12 of them, averaging 5.4% with a median gain of 6.5%. The one exception in that recent stretch was 2018, when the index dropped 14.0% in the fourth quarter alone.

Historical sample (since 1950)	Number of years	Years Q4 finished higher	Hit rate	Average Q4 return
All years, any YTD level entering Q4	76	~61	80.3%	4.2%
Years up 10% or more YTD entering Q4	31	26	83.9%	not separately reported
Years up 10%-20% YTD entering Q4 (2026's band)	21	18	85.7%	5.3%
Most recent 13 years, any YTD level	13	12	92.3%	5.4% (median 6.5%)

Two separate analyses -- one from Motley Fool covering 1950-onward entries above a flat 10% YTD threshold, one from Carson Group narrowing to the 10%-20% band specifically -- point the same direction: a strong first three quarters has historically been followed by more of the same, not mean reversion, in the fourth quarter. Neither data set implies causation; a market already up double digits by September is usually one with earnings growth and momentum behind it, and momentum has historically persisted more often than it has reversed.

Where 2026 actually sits in that distribution

At 11.8% YTD, 2026 sits in the lower part of the 10%-20% band rather than its middle. That matters because the base rate is not a single number -- a year up 19% YTD behaves differently from a year up 11% YTD even within the same labeled "band," since the higher end has less room left before valuations become the binding constraint rather than earnings. On that point, this site's own coverage of the Shiller CAPE ratio hitting 40.9 in September -- the second-highest reading on record -- and of S&P 500 concentration surpassing its 1932 record are both relevant context: the index's advance in 2026 has been unusually reliant on a small number of mega-cap technology names, and Detrick's own data notes technology alone is roughly 39% of the index weight. A double-digit-YTD setup with narrow leadership is not the same setup as a double-digit-YTD year with broad participation, even though both would show up identically in a table that only tracks the headline percentage. Neither the Motley Fool nor the Carson Group analysis breaks its historical sample down by concentration level, which is itself worth flagging: the 21-year and 31-year track records treat every qualifying year as interchangeable, when in practice a year like 1998 or 1999 -- also narrow, mega-cap-led advances -- sat in the same YTD band as a year with broader small- and mid-cap participation. Averaging across both types of years produces a single hit rate, but it does not tell you which type of year is more likely to be the exception.

The years the pattern broke: 1987 and 2018

Base rates describe the middle of a distribution, not its tails, and the two years worth studying are the ones that fell outside it. The more extreme case is 1987. By late August of that year the Dow Jones Industrial Average had gained 44% over the preceding seven months, according to the Federal Reserve's own historical account of the period, and the S&P 500 had roughly tripled since August 1982 to a closing peak of 336.77 on August 25, 1987. On October 19, 1987 -- Black Monday -- the S&P 500 fell 20.47% in a single session, still the largest one-day percentage decline in the index's history, and the index bottomed near 230.30 in November, a 31.6% drop from the August peak. What makes 1987 instructive rather than simply frightening is what happened next: because the first eight months had been so strong, the S&P 500 still closed the full calendar year 1987 up 5.25% on a total-return basis. A trader looking only at the year-end number would have seen an unremarkable up year; a trader holding through the fourth quarter lived through one of the worst quarters in market history to get there. One figure in this paragraph is carried from secondary accounts and could not be confirmed here against a primary daily series: the November 1987 low of 230.30, and the 31.6% drawdown computed from it. FRED's daily S&P 500 series begins in 2016, and the long monthly series used elsewhere on this site reports monthly averages -- 245.00 for November 1987 -- rather than daily lows. The Federal Reserve History essay cited below gives only the Dow's 22.6% one-session decline.

2018 is the more recent and, for most current investors, more relevant cautionary case. The S&P 500 entered that October with a solid year-to-date gain, and Detrick's data shows it was the single negative fourth quarter of the last 13 years -- a 14.0% decline driven by a combination of Federal Reserve rate-hike concerns and a sharp de-rating in the same mega-cap technology names that had led the year's gains. The mechanism in 2018 is the closer analog to a possible 2026 risk than 1987's crash: it was not a single catastrophic event but a multi-week repricing concentrated in the stocks that had done the most carrying earlier in the year.

What the base rate does and does not tell you

If you are reading the 85.7% hit rate as a reason to add risk into Q4, the historical data supports that lean more often than it contradicts it -- but it is a base rate, not a guarantee, and both of the exceptions this article studies were years that looked strong on the surface for the same reason 2026 does: a narrow set of large, richly valued companies carrying the index average. The honest way to use this data is not as a prediction but as a distribution: most years like this one keep going, roughly one in six or seven do not, and when they don't, the damage tends to show up fast rather than gradually, which is a different risk profile than a slow grind lower. Position sizing and time horizon, not this statistic alone, are what determine whether that one-in-six scenario is tolerable for a given portfolio.

It is also worth being precise about what "entering Q4 up 11.8%" actually measures. The FRED figure used here is a price-level year-to-date change measured through the September 30, 2026 close; it excludes dividends, and it is a single index-level snapshot rather than a breadth-weighted measure of how many individual stocks in the index are participating in the gain. The 21-year and 31-year historical samples cited above appear to use the same type of price-level, calendar-year-to-date measurement, which makes the comparison consistent, but a reader checking this against a different data provider's YTD figure -- one that includes dividends, or that measures from a different starting trading day -- should expect a slightly different number, typically within a percentage point or two, not a different conclusion.

Checklist for reading Q4 seasonality claims

• Check which reference class is being cited -- "all years," "years up 10%+," and "years up 10%-20%" are three different samples with three different hit rates, and headlines often blur which one they mean.
• Confirm the as-of date and YTD figure being used; a 11.8% YTD figure from September 30 is not the same as a mid-August figure, and markets move enough in six weeks to shift which historical band applies.
• Look at breadth alongside the index-level return -- concentration data (see this site's coverage of the 1932 concentration record) tells you whether the YTD gain reflects the whole market or a handful of stocks.
• Treat 1987 and 2018 as the shape of the tail risk, not as reasons to dismiss the base rate entirely -- both existed alongside 26-of-31 and 18-of-21 track records that were accurate the rest of the time.

This article is for general investment education and is not personalized investment, tax, or legal advice. Historical seasonality patterns describe past frequencies and do not guarantee future results; all figures are sourced as noted and are accurate as of their stated dates.

FAQ

How much was the S&P 500 up in 2026 through September?

It closed at 7,651.54 on September 30, 2026, which is 11.8% above the 2025 year-end close. That is a price-level change and excludes dividends, so a total-return figure for the same stretch will be slightly higher.

How often is the fourth quarter positive for the S&P 500?

Across all years since 1950, Carson Group's data has the index finishing Q4 higher 80.3% of the time, with an average gain of 4.2%. That is the best record of the four quarters on both counts.

What has happened when the index entered October up 10% to 20%?

That setup has occurred 21 times since 1950. The index finished the fourth quarter higher in 18 of them -- an 85.7% hit rate -- with an average Q4 gain of 5.3%, above the all-years average of 4.2%.

When did the pattern break?

1987 and 2018 are the two cases this article works through. On October 19, 1987 the S&P 500 fell 20.47% in a single session, still the largest one-day percentage decline in the index's history, and yet calendar 1987 still finished up 5.25% on a total-return basis because the first eight months had been so strong. In 2018 the index fell 14.0% in the fourth quarter alone.

Does an 85.7% hit rate mean the fourth quarter of 2026 will be higher?

No. It is a base rate drawn from 21 observations, not a forecast: roughly one year in six or seven with this setup finished the quarter lower. Neither the Carson Group nor the Motley Fool sample separates years by how concentrated the index gain was, which is the specific feature that makes 2026 unusual.

Why does this figure differ from the year-to-date number another provider shows?

Providers differ on whether dividends are included and on which trading day the year is measured from. The figure used here is the price-level change from the 2025 year-end close to the September 30, 2026 close, taken from the S&P Dow Jones Indices series distributed by FRED.

Sources

• FRED (Federal Reserve Bank of St. Louis), S&P 500 daily close series, data by S&P Dow Jones Indices -- closes used here: 6,845.50 on December 31, 2025 and 7,651.54 on September 30, 2026
• Trading Economics -- U.S. Stock Market (S&P 500 level and YTD change, as of 2026-09-30)
• Benzinga -- Ryan Detrick / Carson Group Q4 seasonality analysis
• The Motley Fool -- S&P 500 Q4 track record since 1985 and since 1950
• Federal Reserve History -- Stock Market Crash of 1987
• Black Monday (1987) -- market levels and single-day decline
• Slickcharts -- S&P 500 total returns by year (1987 full-year figure)

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