Stock Market Seasonality: Which Months Show the Worst and Best Performance?

Over the long sweep of market history, one truth stands out clearly: the stock market trends upward. The Dow Jones Industrial Average, S&P 500, and Nasdaq Composite have all demonstrated this fundamental pattern across the decades. Yet the journey to that endpoint involves significant turbulence along the way. Over any given two-year stretch, investors can witness both record highs and bear market lows—sometimes within months of each other. This reality underscores a critical lesson: while the market’s long-term direction is reliably positive, short-term movements remain notoriously unpredictable.

However, history reveals something remarkable about this unpredictability. Statistical analysis spanning nearly a century—compiled by research firm Yardeni Research—identifies clear seasonal patterns in market performance. Certain months have consistently rewarded investors, while others have just as consistently challenged them. Understanding which worst months for stock market performance tend to occur, and why they occur, can help investors contextualize short-term volatility within a larger strategic framework.

A Century of Data: The Best-Performing Months in Stock Market History

The optimism embedded in long-term stock market investing has deep roots. Since 1928, the S&P 500 has finished positive in 64 years compared to just 31 declining years. Beyond the annual level, the data becomes even more granular and revealing. Four specific months have historically delivered outsized returns.

Based on 95 years of performance data, only four months have consistently produced an average annual gain exceeding 1% for the S&P 500:

• July: 1.7% average annual gain
• April: 1.4% average annual gain
• December: 1.3% average annual gain
• January: 1.2% average annual gain

The reasons underlying these patterns offer valuable insight. December and January benefit from the so-called “Santa Claus rally”—a period when investor sentiment typically brightens as the year winds down and fresh optimism arrives with new year. This psychological boost frequently translates into tangible market gains.

July’s dominance stems largely from a technical factor: index rebalancing that occurs in June. As fund managers refresh their holdings, removing laggards and adding outperformers to major indices like the S&P 500, this rotation often provides a lift to overall market levels. When July closes in positive territory, the gains are particularly pronounced. Historically, July has finished higher 57 times since 1928, and in those up months, the average gain reached an impressive 5%.

April ranks as the second-strongest performer on an average-gain basis, delivering a 4.3% average return when it finishes in the black. Yet when measuring sheer consistency—the total number of times a month closes higher—December takes the crown. The S&P 500 has finished December higher 69 times over the same 95-year period, giving this month an exceptional track record of positive outcomes.

The Worst Months for Stock Market: Historical Weakness Patterns

If certain months deserve investor celebration, others warrant caution. Since 1928, precisely three months have produced average annual losses for the S&P 500—making them the worst months for stock market participants historically:

• September: (1.1%) average annual loss
• February: (0.1%) average annual loss
• May: (0.1%) average annual loss

The logic behind February and May weakness appears connected to profit-taking. Following the strong performances registered in December, January, and April, investors frequently lock in gains during these spring and early-year months. The market consolidates, and pullbacks become commonplace.

September presents a different dynamic. As summer vacation concludes and traders return to their desks with renewed focus, trading activity increases. Often, investors liquidate positions to harvest gains accumulated during the lower-volume summer months, creating downward pressure. This “end of summer” phenomenon has proven remarkably consistent across market cycles.

The worst months for stock market performance also display distinctive risk characteristics when they do decline. May, September, and October have each experienced average losses of (4.7%) during their down months—the largest average declines in the dataset. October deserves particular attention given its association with major historical crashes, most notably the Black Monday Crash of 1987, which stands as one of the most severe single-day market collapses ever recorded.

When examining frequency, September emerges with the unwanted distinction of being the worst month overall. The S&P 500 has closed lower in September 52 times since 1928, compared to just 42 positive closes and one unchanged month (September 1979). February follows as the second-worst performer, with 46 declining months versus 50 positive closes.

Understanding the Drivers Behind Monthly Patterns

The seasonality observed in stock markets reflects a complex interplay of factors. Some are psychological—the collective mood shifts associated with year-end holidays or summer endings. Others are mechanical—fund rebalancing cycles, quarterly earnings announcements, and fiscal calendar adjustments. Tax-loss harvesting in late fall can suppress prices, while the “Santa Claus rally” provides genuine economic optimism mixed with year-end bonus spending.

Yet it is crucial to recognize that these patterns, while statistically significant, are not deterministic. Every month contains surprises, and historical frequency does not guarantee future results. Attempting to time trades based on seasonal signals introduces its own risks and costs.

The Real Guarantee on Wall Street: Time and Patience

If seasonal patterns offer only probabilistic guidance, what represents the closest thing to a genuine guarantee in equity markets? The answer lies not in finding the worst months or best months, but in adopting an extended time horizon.

Market analytics firm Crestmont Research periodically refreshes analysis examining rolling 20-year total returns for the S&P 500, including all dividends reinvested. Using data back-tested to 1900 (based on S&P 500 predecessors), Crestmont analyzed 104 distinct rolling 20-year periods spanning from 1919 through 2022.

The results proved unambiguous: every single 20-year holding period delivered positive annualized returns. A 100% success rate across 104 separate rolling periods—regardless of entry point, market conditions, or timing—represents a genuine market truth.

This finding cuts through the noise of seasonal performance data. Whether an investor was fortunate enough to purchase the S&P 500 during a bear market trough or unfortunately timed entry at a short-term peak became immaterial. What mattered was the commitment to hold for two decades. In every instance, patience generated wealth.

Reconciling the Short Term with the Long Term

The statistical evidence on worst months for stock market performance serves a valuable purpose: it contextualizes short-term volatility. Knowing that September has historically been challenging, or that July typically shines, helps investors understand that market weakness is neither unprecedented nor permanent. These patterns are features of market history, not flaws in the investment thesis.

Yet the broader lesson transcends monthly seasonality. While certain months have indeed proven statistically weaker, the worst-performing individual months pale in significance compared to the power of decades of compounding returns. The investor who abandons their position during a historically weak September, only to miss the subsequent recovery, forfeits returns that dwarf any tactical benefit.

In the end, the stock market’s worst months matter far less than the investor’s response to them. For those with the patience to hold through all seasons—both the historically strong and the historically weak—the data offers a powerful promise: time in the market remains the most reliable path to wealth creation.