Stock Analysis
The September Curse: -1.2% a Year, Every Year, for Nearly a Century
Every year, without fail, the same unsettling pattern shows up on trading screens worldwide — and Dalal Street is no exception. September is, on average, the worst-performing month for global stock markets, a trend that has held for nearly a century and shows up not just on Wall Street but across the FTSE, Nikkei, and Euro Stoxx too. Since 1928, the S&P 500 has averaged a return of roughly -1.13% to -1.2% in September, making it the only month with a consistently negative long-run track record. This isn't a one-off anecdote from a bad year — it shows up across nearly 100 years of data and multiple global indices. And this year, the pattern isn't playing out in a vacuum for Indian investors either: Sensex and Nifty have already been under pressure from rising oil prices and Iran-US tensions, layering fresh macro stress on top of a seasonal effect global markets have quietly watched for a century. Understanding why September behaves this way matters for anyone deciding whether to sit tight, rebalance, or brace for volatility as the year heads into its final quarter.
The Key Numbers
The pattern holds across nearly a century of data. Since 1950, the S&P 500 has posted an average September return of -0.6% to -0.7%, the weakest of any calendar month — and since 1928, the average sits closer to -1.13% to -1.2%, depending on the dataset used. Zooming into shorter, more recent windows makes the pattern look even sharper: the index has averaged a 4.2% drop over the last five Septembers and more than 2% over the last ten.
It's not that September loses more often — it loses bigger. Data from Wedbush Securities shows the S&P 500 posted gains in only 42 of the last 95 Septembers, versus losses in 53. Yet during the "up" Septembers the average gain was a modest 3.19%, while the "down" Septembers averaged a steeper 4.70% loss — an asymmetry that drags the long-run average into negative territory even though positive Septembers aren't rare.
The effect isn't unique to the US, and that's exactly why Indian investors shouldn't tune it out as a foreign statistic. A 50-year analysis across four major global indices — the S&P 500, FTSE 100, Nikkei 225, and Euro Stoxx 50 — found all four close September lower on average, with the Euro Stoxx 50 falling hardest at -2.13%, followed by the FTSE 100 (-0.98%), the S&P 500 (-0.88%), and the Nikkei 225 (-0.83%). If a pattern this consistent shows up across markets with entirely different structures, regulators, and investor bases, it's reasonable to expect Indian markets sit somewhere on that same spectrum, even without a dedicated Sensex-specific dataset to point to.
Recent Septembers have kept the streak alive globally. The S&P 500 fell 4.9% in September 2022, 9.3% in September 2021, 4.8% in September 2020, and 3.9% in September 2019 — four consecutive years of meaningful September declines before more recent mixed results.
What's Driving This
The leading theory: bad news travels slower than good news. INSEAD finance professor Lily Fang's research points to an information-asymmetry explanation — when a company releases good news, any investor can act on it immediately by buying, so the price adjusts fast. Bad news is different: only people who currently hold the stock can act right away by selling, meaning the market for that information to fully price in is structurally smaller and slower. Over time, this creates a lagging, slow-burn drag rather than a single sharp shock — one explanation for why September's weakness shows up as a grind rather than a crash.
Institutional rebalancing adds mechanical selling pressure. September marks the end of Q3 and, for many global mutual funds, the close of their fiscal year — a period when portfolio managers commonly sell underperforming positions to lock in tax losses or clean up holdings before reporting season, adding real sell-side volume independent of any specific news event. For India, this matters directly: a chunk of this selling comes from the same foreign institutional investors (FIIs) who move in and out of Indian equities, meaning global fiscal-year-end rebalancing can show up as FII outflows here too.
Investors returning from summer reassess risk all at once. With trading volumes typically lighter through July and August in Western markets, September often functions as a global re-entry point where accumulated economic data, earnings previews, and macro headlines all get digested and repriced in a compressed window — amplifying whatever news backdrop already exists, and Indian markets absorb that repricing through FII flows and global risk sentiment even when the trigger originates elsewhere.
This year's setup adds extra ingredients — and India is feeling more than one of them directly. Analysts note that when September opens with global valuations elevated and geopolitical risk live, the conditions are ripe for the seasonal pattern to compound with fundamental repricing rather than offset it. For Indian markets specifically, rising crude oil prices tied to Iran-US tensions in the Persian Gulf hit doubly hard: India's large net-oil-importer status means a Gulf flashpoint doesn't just dent global sentiment, it widens the trade deficit and stokes inflation at home — a structural vulnerability that resurfaces every time tensions rise in the region.
The Silver Lining Nobody Mentions First
October, despite its reputation for crashes, tends to be a recovery month globally. Despite popular fear of an "October Effect" given famous crashes like 1929 and 1987, October has actually delivered an average return of about 0.9% historically — a rebound, not a continuation of September's weakness. The Euro Stoxx 50 shows this most dramatically, averaging +2.82% in October versus -2.13% in September, a swing of nearly 5 percentage points.
The months following September are historically strong worldwide. November, December, and January are among the strongest average-return months going back to 1950 — meaning investors who stayed the course through a weak September have historically been rewarded fairly quickly afterward. If global risk appetite recovers into Q4 the way it has historically, that's typically a tailwind for FII flows into Indian equities too, not just developed markets.
Context and Nuance: Is the September Effect Actually Predictive?
The case that it's a real, tradeable pattern: The consistency is hard to dismiss outright — this shows up across a century of US data and across four independent global indices with different market structures, regulatory regimes, and investor bases. A pattern this persistent, appearing in unrelated markets, suggests something structural (fund-flow mechanics, fiscal-year-end rebalancing) rather than pure coincidence — and structural, flow-driven effects tend to transmit into Indian markets through FII behaviour even when the origin is elsewhere.
The case for skepticism: Even Investopedia's own analysis of the phenomenon notes the evidence tying it specifically to the calendar is "flimsy at best" — and the win rate data actually undercuts the doom narrative: stocks have risen in September slightly more often than they've fallen over the past century (51% vs. 49%), per Investopedia's count, and the CME's data puts underperformance at around 55% of Septembers, not the near-certainty the "worst month" label implies. What pulls the average down isn't frequency of losses — it's that the down years tend to be sharper than the up years are strong, a statistical artifact that says less about September being cursed and more about a handful of severe outlier years (2008, 2001, 2022) doing the heavy lifting.
For Indian investors specifically, there's an added layer of nuance: even if the "September Curse" itself is a global statistical pattern rather than an India-specific one, this particular September is compounding it with a very real, India-specific driver — oil-price-sensitive currency and inflation dynamics — which makes this year harder to write off as "just seasonality." Whether you treat September as a reliable warning sign or a coincidence dressed up as a pattern likely depends on your time horizon: traders positioning for weeks may find it actionable, while long-term investors are better served largely ignoring it.
What This Means for Different Readers
For long-term, buy-and-hold investors in Indian equities: The S&P 500 has still delivered roughly 8% annualized returns since 1950 despite the September drag, and the index has been profitable over every rolling 20-year period in its history. Indian equities have broadly followed a similar long-run compounding story — a weak September historically hasn't mattered much if your holding period is measured in years, not weeks.
For active traders on Sensex and Nifty: The asymmetry between down-September severity (-4.70% average globally) and up-September mildness (+3.19% average) suggests hedging or reducing position size heading into September may be more useful than trying to predict direction outright — especially with oil-linked volatility adding an extra layer of unpredictability this year.
For anyone tempted to sell in a September dip: History shows October, and the months following it, have tended to recover the ground lost globally — selling into September weakness has historically meant selling near a seasonal low, not avoiding one.
For this particular September in India: With Sensex and Nifty already under pressure from Iran-US tensions and elevated crude prices, and FIIs recently net sellers, the seasonal pattern isn't happening in a vacuum this year — it's layering on top of a real, identifiable macro trigger, which is a different situation than a "pure" seasonal dip.
Frequently Asked Questions
What exactly is the September Effect? It's the well-documented historical tendency for stock markets worldwide to post their weakest average monthly returns in September, with the S&P 500 averaging roughly -0.6% to -1.2% depending on the measurement period, making it the only month with a consistently negative long-run average since 1928.
Is September actually the worst month more often than not, or just on average? Not necessarily more often — Investopedia's data shows stocks have actually risen in September slightly more often than they've fallen historically (51% vs. 49%) — but the losing Septembers tend to be considerably steeper than the winning ones, which pulls the average into negative territory.
Does the September Effect happen in markets outside the US, including India? A 50-year study of the S&P 500, FTSE 100, Nikkei 225, and Euro Stoxx 50 found all four indices closed September lower on average, with declines ranging from -0.83% (Nikkei 225) to -2.13% (Euro Stoxx 50). While there's no dedicated long-run Sensex dataset cited here, Indian markets are exposed to the same global FII flow and risk-sentiment mechanics that drive the effect elsewhere.
Why does bad news specifically affect September performance? Research by INSEAD's Lily Fang suggests markets absorb bad news more slowly than good news, because only existing stockholders can sell on negative information right away, while anyone can buy on positive news — creating a slower, more drawn-out repricing process that may compound during September's seasonal patterns.
Should Indian investors sell stocks before September or during a September decline? Historical global data doesn't clearly support this — October has averaged a positive return of about 0.9% following September's weakness, and the following months (November through January) are among the strongest of the year, suggesting investors who exit during September dips have often sold near a low rather than avoided one.
What other factors, besides seasonality, are affecting Indian markets this September? Rising crude oil prices tied to Iran-US tensions in the Persian Gulf, continued FII selling, and lingering uncertainty around the US Fed's rate path are all compounding on top of the seasonal pattern this year — making this September a case of real fundamental pressure layered onto a statistical tendency, not a "pure" seasonal dip.
At a Glance
Metric | Value |
S&P 500 average September return (since 1928) | -1.13% to -1.2% |
S&P 500 average September return (since 1950) | -0.6% to -0.7% |
S&P 500 average September return (since 2000) | -1.4% |
Positive vs. negative Septembers (Wedbush, 95 years) | 42 positive / 53 negative |
Average gain in "up" Septembers | +3.19% |
Average loss in "down" Septembers | -4.70% |
S&P 500 average October return (recovery month) | +0.9% |
Global index average September decline (50-yr, 4 indices) | ~1.2% average |
Weakest global index in September | Euro Stoxx 50 (-2.13%) |
S&P 500 long-run annualized return (since 1950) | ~8% |
India-specific factor this September | Oil prices + Iran-US tensions pressuring Sensex, Nifty |
Sources:
Motley Fool "September Effect Statistics": https://www.fool.com/research/september-effect-statistics
Motley Fool "Is the September Effect Real?": https://www.fool.com/terms/s/september-effect
Yardeni Research (via Motley Fool): https://www.fool.com/terms/s/september-effect
Benzinga/LPL Financial: https://www.benzinga.com/24/09/40676774/september-market-seasonality-why-this-month-is-historically-the-toughest-for-investors
Wedbush Securities: https://www.benzinga.com/24/09/40676774/september-market-seasonality-why-this-month-is-historically-the-toughest-for-investors
Finder "The September Effect": https://www.finder.com/uk/share-trading/share-trading-research/september-effect
Disclosure:This article is published by KuberHunt for informational and educational purposes. KuberHunt is a technology and research distribution platform connecting investors with SEBI-registered Research Analysts and Investment Advisors. KuberHunt itself is not a Research Analyst or Investment Adviser and does not provide investment advice, create, or endorse any specific investment recommendation. This article does not constitute investment advice, and should not be used as the basis for any buy, sell, or hold decision on any security mentioned. Readers should consult a SEBI-registered professional before making investment decisions.
Data Accuracy / Fact-Check Note:Index opening figures varied slightly across sources depending on the exact timestamp captured (pre-open, first-minute, and 9:24 AM snapshots all differ marginally). Readers should confirm final closing figures against the official NSE/BSE bhavcopy rather than relying on the early-trade figures cited in this article.
Educational content, not investment advice. Markets carry risk; read the disclosures on any Reco before you act on it.
Educational content, not investment advice. Markets carry risk; read the disclosures on any Reco before you act on it.