The 3 Best Artificial Intelligence (AI) Stocks for September

The September Effect is a well-known phenomenon where the S&P 500 tends to post negative returns in September. This pattern has persisted for nearly a century, with a long-run average return of around -1.1% between 1928 and 2025. The cause of this decline is often attributed to portfolio managers returning from summer vacations and rebalancing their portfolios, leading to increased selling pressure.

In 2009, a rare signal called the "Double Down" flashed for Nvidia, a chipmaker, marking the first time in years that a similar signal appeared for a company 1/100th its size. This year, investors should pay attention to the September Effect, particularly in the context of AI stocks. The Magnificent Seven, which includes Nvidia, Apple, Alphabet, Microsoft, Amazon, Tesla, and Meta Platforms, now account for nearly 34% of the S&P 500's value. Over the last three Septembers, the performance of these AI giants has been mixed.

While AI companies are growth stocks with high duration, meaning they can fall further and faster than average, recent years have shown that supportive interest-rate environments, continued capital expenditures, and compounding earnings can outweigh seasonality. Historically, assets like gold, short-duration Treasuries, and traditional defensive sectors such as utilities, consumer staples, and healthcare have performed well during September.

These assets tend to be less vulnerable to narratives around geopolitics or monetary policy changes.

The best approach for investors during weaker periods is not to liquidate long-term AI or technology allocations but to treat the month as a stress test of position size. Trimming into momentum and balancing with safe-haven assets can help respect historical odds without attempting to time the market.