The worst day of the year for U.S. stocks has arrived!

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As U.S. stocks rebounded strongly this week, a historical pattern is quietly approaching—the U.S. tax filing deadline on April 15 is, on average, the worst-performing trading day for the S&P 500 throughout the year in terms of seasonal data.

According to historical data, since 1990, the median daily return of the S&P 500 around April 15 ranks at the bottom among all trading days. The market generally believes this is closely related to investors being forced to liquidate assets before the deadline to pay tax bills. Although the Federal Reserve actively manages market liquidity around the tax deadline, historical data shows that this liquidity injection is on average still insufficient to prevent the stock market from falling.

This week, overall market sentiment is optimistic. The S&P 500's overnight closing price is significantly higher than the level before the recent escalation of geopolitical tensions, and investors seem to be trying to put recent risk events behind them. However, the seasonal pattern suggests short-term downward pressure remains, and investors need to stay alert.

Tax Deadline Drags Down the Stock Market: Clear Historical Pattern

Looking back at data since 1990, the two worst-performing dates for the S&P 500 in terms of median return among all trading days are April 15 and June 7.

The negative effect of April 15 has a relatively direct explanation: it is the annual deadline for U.S. personal income tax filings, and a large number of investors must liquidate their positions before the last deadline to raise cash for taxes, resulting in concentrated selling pressure.

The pattern on June 7 is relatively perplexing. Although there is a less important tax-related date in mid-June, why the selling pressure emerges ahead of that date remains unclear.

It is worth noting that the above dates are not always trading days. If they fall on a non-trading day, they are postponed, so the actual impact dates may be somewhat shifted.

Federal Reserve Intervenes in Liquidity Management, With Limited Effect

Around the tax deadline, the Federal Reserve actively manages liquidity. Typically, before the April deadline, the balance in the Treasury’s account at the Fed decreases, meaning liquidity is injected into the market; after the deadline, as taxes are gradually paid into government accounts, the balance rises again.

However, historical seasonal data shows that this precautionary liquidity injection is on average still insufficient to offset downward pressure on the stock market. In other words, even with the Fed's buffering operations, stock market weakness around the tax deadline remains a statistically significant pattern.

Short-Term Risks and Rebound Potential Coexist

Beyond seasonal patterns, the current market faces a more complex tug-of-war between bullish and bearish factors.

On the bearish side, even if this year repeats the historical pattern, the impact may be limited to the short term. Historical data also shows that after April 15, the S&P 500 generally posts positive returns for the remainder of April, making the seasonal pressure relatively limited.

However, May is one of the months with the lowest average returns for the year overall. The market adage "Sell in May" may, to some extent, be a self-fulfilling prophecy.

On the bullish side, current pessimism among retail and institutional investors is at a relatively high level, and this consensus on bearishness itself may become a catalyst for a rebound—short-covering or renewed risk exposure may both push the market higher in the coming weeks. This week’s rebound may mark the beginning of this process.

Ultimately, seasonal patterns are only reference anchors and need to be adjusted in combination with the current market environment. For investors, being cautious around the tax deadline and paying attention to the potential subsequent short-covering rally may be a balanced strategy at present.

Risk Warning and DisclaimerThe market has risks; investments require caution. This article does not constitute personal investment advice and does not take into account the particular investment goals, financial situations, or needs of individual users. Users should consider whether any opinions, views, or conclusions in this article are appropriate for their specific circumstances. If you invest accordingly, you do so at your own risk. ```