At the beginning of 2026, the U.S. stock market got off to a positive start. As of the close on January 15, the S&P 500 Index has gained nearly 2% year-to-date and is on track for a strong January performance. For investors who were concerned about high stock market valuations and a potential bubble at the end of 2025, this is undoubtedly good news.
But does a good start in January usually indicate that the stock market will perform well for the entire year? By reviewing the performance data of the S&P 500 Index over the past 30 years, we can analyze the predictive power of the so-called “January Effect.”
Historical Correlation: Only a Moderate Indicator
Analyzing data from the past 30 years, the correlation between the S&P 500’s performance in January and its performance for the full year is approximately 0.42. This indicates a moderately positive relationship, but not a strong one. This means that while a connection does exist, investors should not assume that January’s performance will “determine” the direction for the rest of the year.
However, when we break down the data by different January performance levels and compare them to their corresponding annual returns, clearer patterns emerge:
| S&P 500 January Performance | Occurrences | Average Annual Return |
| Down More Than 5% | 5 | -7.01% |
| Down 2% to 5% | 5 | 10.57% |
| Slightly Down (0 to -2%) | 2 | 1.76% |
| Slightly Up (0 to 2%) | 6 | 16.42% |
| Up 2% to 5% | 7 | 10.02% |
| Up More Than 5% | 5 | 21.42% |
(Data Source: Google Finance, yCharts)
Two key phenomena are immediately noticeable from the table above:
Warning from Extreme Declines: When January performance is very poor (a decline exceeding 5%), it indeed corresponds to the worst average annual return (-7.01%). For example, the last major market crash occurred in 2022, when the S&P 500 fell 19% for the year, and it had already dropped about 5.3% in January of that year. Similarly, during the 2008 financial crisis, the index fell more than 6% in January and ultimately plunged 38% for the year.
Positive Signal from a Strong Start: On the other hand, when January gains exceed 5%, it usually also indicates strong average performance for the full year (with an average annual return of 21.42%).
One important takeaway is: unless January sees a particularly severe decline, the stock market overall still tends to rise, but this is by no means an absolute guarantee. For instance, during the dot-com bubble burst in 2002, the index fell 23% for the year, but it only declined slightly by 1.6% in January.
How Can Investors Protect Their Portfolios?
Unfortunately, market crashes are difficult to predict. They can happen suddenly and without warning. Therefore, it is always crucial to take steps to protect and diversify one’s investment portfolio, especially for investors nearing retirement or those with near-term liquidity needs.
In this context, investors may consider: focusing on defensive sectors, pay more attention to dividend stocks, utility stocks, and stocks with low volatility (weak correlation with S&P 500 movements), while puttin primary focus on value stocks and avoid those with excessively high valuations.
By taking these measures, investors can at least reduce some of their overall risk while avoiding missing out on potential gains by adopting overly conservative strategies (such as selling all holdings). In short, when short-term market fluctuations are unpredictable, building a balanced and somewhat defensive portfolio is a wiser long-term strategy.
