Since 1950, September has historically delivered bearish stock market performance across major indexes, with all-year averages dropping 0.6% to 0.8% by month-end. Midterm-election years significantly amplify this weakness through four-phases:
► Sep 1–8 (Tue–Tue) = Trading Days 1–5: Sideways-to-up / modestly higher. Most midterm series (especially Russell 2000 and DJIA) rise, with several peaking near +0.5% to +1.0%.
► Sep 9–17 (Wed–Thu) = TD 6–12: Sideways to mildly fading. Early gains are largely held or only slowly given back. S&P 500 midterm often remains the strongest (still near its peak), while NASDAQ and Russell lines begin drifting lower.
► Sep 18–25 (Fri–Fri) = TD 13–18: Steady decline. The mid-month advantage disappears; indices trend lower and most move into negative territory.
► Sep 28–30 (Mon–Wed) = TD 19–21: Accelerating sell-off / sharp weakness. Losses deepen, particularly in NASDAQ and Russell 1000 (historically finishing around –1.6% to –1.8%). Russell 2000 also shows a late plunge.
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