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What Is the September Effect?

By Lyle DalyUpdated Sep 30, 2025 at 3:35 PM | Fact-checked by Frank Bass

Key Points

  • The S&P 500 typically dips in September, with a -1.13% average return.
  • September's stock decline may relate to tax loss harvesting or quarter-end rebalances.
  • Despite the "September Effect," keep normal investing strategy as monthly trends vary.

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