September is the Cruelest Month

September 04, 2024 | Evan Frazier, CFA, CAIA, Senior Research Analyst

The S&P 500 Index pulled back by more than 2% yesterday in a move that is not unprecedented based on the history of the benchmark. Specifically, the bellwether equity index has averaged a return of roughly -0.7% in the month of September dating back to 1928, which is particularly striking given that average performance of the benchmark has been positive in every other month of the year. There are several possible explanations for the potential anomaly that some have dubbed the “September Effect.” First, sales by investors returning from summer vacations aiming to lock in taxable gains or losses prior to the end of the year could be a driving force behind lackluster September returns. Additionally, September could see higher levels of equity sales due to market participants seeking to fund tuition costs for their children prior to a new academic year. The September Effect could also be seen as a self-fulfilling prophecy, as expectations for poor near-term equity returns could lead to widespread investor selling.

It is important to highlight a few points related to the September Effect that may assuage concerns related to equity performance over the coming weeks. First, many economists chalk the September Effect up to pure chance, given that any persistent market anomaly would be exploited by investors, causing it to disappear over time. It is also important to remember that the S&P 500 Index has actually notched a positive return in roughly 52% of September months dating back to 1928, meaning that the average figure cited in the first paragraph is skewed by a few negative observations of significant magnitude. As it relates to this year, several factors could buoy equity prices in the near term, including resilient corporate earnings, moderating inflation, and a high probability of a reduction in interest rates by the Federal Reserve at its meeting later this month. While challenges also face equity markets at present, market participants should remain disciplined as it relates to portfolio allocation and adhere to long-term investment policy objectives. Indeed, while the September Effect may serve as a notable phenomenon worthy of additional study, it ultimately should not factor into the investor decision making process.

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