Why September Stands Out If you’ve heard of the “September Effect,” you already know the reputation. Over a century of data, every month of the year has averaged a positive return for the S&P 500—except September. Its historical average is a decline of about 0.8%. At the other end of the spectrum sits July, the strongest month, with an average gain of nearly 2%. In 2025, July (and August) lived up to that record, delivering fresh all-time highs for the index. Is September doomed to weak performance just because it has followed the good vibes of summer? Let’s dig deeper to understand what is behind these numbers. Frequency and Outliers What makes September unusual isn’t just the size of its average decline. It’s also the frequency. About half of all Septembers finish in the red, compared to the typical month, which is positive nearly two-thirds of the time. But the averages hide the real story. If you look closer, September’s record is heavily influenced by about 10 extreme downturns since the 1920s. These coincided with global events and systemic stress—like the Great Depression, the dot-com collapse, and the 2008 financial crisis. Remove just 10 outlier Septembers, including three from the Great Depression alone, and the month shifts from negative to positive. That tells us September’s reputation comes less from built-in seasonal weakness and more from a handful of extraordinary moments in market history. Context for Today Fast forward to today: we don’t see the same structural cracks that defined those historically bad Septembers. Surprises are always possible—markets have a way of delivering the unexpected—but current conditions look very different from the environments that produced those extreme outliers. It’s also important to note the setup. After a strong 2025 summer run, with the S&P 500 posting multiple new highs, some cooling off is normal. What Investors Can Do At Vector, we emphasize a disciplined approach to rebalancing. After strong gains, rebalancing means trimming back what has grown ahead of expectations and reallocating towards other areas . This helps manage concentration risk and turns volatility into an opportunity. So, is September truly cursed? Unlikely. More than anything, it reminds us that markets don’t move in straight lines—and even one of the world’s most consistent wealth-building engines has its off months. The long-term trend remains clear: growth outweighs the setbacks. A diversified plan, paired with conditions-based rebalancing, provides the steady foundation investors need—through Septembers, through Octobers, and well beyond. -- Contact us: vectorwealth.com/contact or schedule an intro call: https://www.vectorwealth.com/start - Disclosures and Regulatory vectorwealth.com/regulatory - All content discussed in our podcasts, videos, or related blog articles are for informational purposes and should not be construed as individualized financial advice. Opinions expressed herein are solely those of Vector Wealth Management, our staff, and guests. Material presented is believed to be from reliable sources, however, we make no representations as to its accuracy or completeness. All information and ideas should be discussed directly and in detail with your financial advisor prior to implementation of a strategy or investment. This podcast and related content are not intended to render personalized investment advice, nor should it be viewed as an offer to buy or sell, or a solicitation of any offer to buy or sell the securities or strategies discussed. Please note that neither Vector Wealth Management nor any of its agents give legal or tax advice. The firm is not engaged in the practice of law or accounting. Charts, graphs, and returns do not represent the performance of Vector Wealth Management or any of its advisory clients. Returns presented do not reflect the impact that advisory fees and other expenses would on the results. Different types of investments involve varying degrees of risk, and there can be no assurance that any specific investment, asset category, or strategy will be suitable or profitable for a client’s portfolio.
