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Highlights
Long-term seasonal trends indicate September has historically been a weak month for the Australian share market
Benchmark ASX 200 enters September after strong gains in July and August
Analysts explore calendar-driven patterns affecting market performance
The Australian equity sector, represented by benchmark indices like the ASX 200, is often studied through the lens of seasonality—patterns of market behaviour tied to calendar periods. One of the more persistent trends observed over decades is the so-called "September Swoon", a historically challenging stretch for the Australian market that has often followed strong mid-year momentum.
This analysis draws from both long-term and short-term seasonal performance of the ASX to identify whether September maintains its trend of dampened returns and elevated volatility. Key attention is placed on how prior strength in July and August may influence this dynamic.
What is Seasonal Weakness and Why September?
Seasonal weakness refers to periods where market data reveals consistently muted or negative performance over multiple years. Over a four-decade view, September has stood out as the only month with a long-run average return dipping below neutral on total return measures.
This is not just about price action. By analysing the All Ordinaries Total Return Index, which accounts for both price movements and asx dividends, insights become clearer. Price-only indices often misrepresent calendar-based performance, especially in months with heavy ex-dividend activity.
The September slump may be partially explained by macro timing. From post-earnings period fatigue to strategic reshuffling by fund managers returning from the northern hemisphere’s summer, multiple variables converge during this window.
Does Recent Strength Matter for September?
Recent performance often impacts market psychology and structure heading into weaker periods. July and August are generally among the stronger calendar stretches for the ASX 200, and when strength in these months aligns with seasonal averages, the likelihood of a reversionary period rises.
For the current year, the index saw notable advances during these months. This adds context to seasonal expectations for September, as historically, strong rallies leading into this month have sometimes been followed by consolidation or reversal phases.
Shorter-term views—over five, ten, and twenty-year horizons—continue to support September’s reputation. Despite variations, the overall gain reliability and magnitude trend lower than most other months.
How Volatile Does the Market Get?
The volatility aspect of the September period should not be overlooked. Historical data suggests that September often serves as the starting point for a twelve-week window with heightened fluctuations. This volatility has manifested in sharp swings and reversals, influenced by both domestic corporate developments and broader global factors.
Though October is often remembered for dramatic downturns, statistical averages have shown more stability in that month compared to the concentrated swings seen throughout September.
What’s Unique About This Season?
This September arrives after a particularly strong two-month stretch, aligning with earlier seasonal playbooks. With the ASX 200 approaching peak levels, market participants may watch for movements influenced by seasonal effects more closely.
The combination of reporting season fatigue, dividend adjustments, and global fund flows could shape trading behaviours. While no single factor dominates, the confluence of these elements continues to define September as a critical period in Australia’s market calendar.
