How the January Effect Has Evolved Over the Decades

 | Jan 17, 2024 02:46

The January effect, named for the perceived market anomaly where stock returns in January are higher than in other months, has been a subject of interest since it was first written about in 1942.

Traditionally, this effect has been attributed to tax-loss harvesting at the end of the year, where investors dump their laggards to offset capital gains taxes, leading to a December selloff. This is believed to be followed by a buying spree in January, as investors repurchase stocks, boosting demand and prices.

Other explanations for the January effect include the influx of cash from year-end bonuses into the stock market, the rise of tax-sheltered retirement accounts (IRAs, 401(k)s, etc.) and the prevalence of new investment instruments and regulatory changes.

Then there’s also a perceived increase in investment activity as people follow through on New Year’s resolutions to invest more. January, after all, has long been associated with fresh starts and positive animal spirits. A recent YouGov poll found that about a third of American adults made New Year’s resolutions for 2024.

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The January effect may have been a pronounced trend in the past, but in more recent years, it’s delivered diminishing returns.

Take a look at the visual below. It shows average monthly gains for the S&P 500 during two time periods: the 30-year period through the end of 1993, and the subsequent 30-year period through the end of 2023. As you can see in the bar chart on the left, January was the top month for returns, with stocks rising 1.85% in value on average. That’s well above December, the number two month, when the stock market was up an average 1.55%.

Something shifted over the next 30 years, though, and January no longer ranked first, falling to the eighth best month with stocks advancing only 0.28%.