There’s something about December that seems to charm equity markets into a year-end flourish.

For decades, investors have noted how the final month of the calendar tends to bring tidings of green screens and positive returns, fuelling what has become known as the Santa Claus rally.

But behind the festive metaphor lies a consistent, data-backed pattern.

Over the past four decades, the S&P 500 has gained in December about 74% of the time, with an average monthly return of 1.44% –– second only to November.

This seasonal cheer is echoed across European markets, with some indices showing even stronger performances.

Since its inception in 1987, the EURO STOXX 50, the region’s blue-chip benchmark, has posted an average December gain of 1.87%. That makes the Christmas period the second-best month of the year after November’s 1.95%.

More striking, however, is its winning frequency. December closes in positive territory 71% of the time — higher than any other month.

The best December for the index came in 1999, when it surged 13.68%, while the worst was in 2002, when it fell 10.2%.

Rally gathers steam in late December

Zooming in on country-level indices further reinforces the seasonal trend.

The DAX, Germany’s flagship index, has shown an average December return of 2.18% over the past 40 years, trailing only April’s 2.43%. It finishes the month higher 73% of the time, again tying with April for the best track record.

France’s CAC 40 follows a similar pattern, gaining on average 1.57% in December with a 70% win rate, also ranking it among the top three months.

Spain’s IBEX 35 and Italy’s FTSE MIB are more moderate but still show consistent strength, with December gains of 1.12% and 1.13% respectively.

But the magic of December doesn’t usually kick off at the start of the month. Instead, the real momentum tends to build in the second half.

According to data from Seasonax, the EURO STOXX 50 posts a 2.12% average return from 15 December through year-end, rising 76% of the time.

The DAX performs similarly, gaining 1.87% on average with a 73% win rate, while the CAC 40 shows even stronger second-half returns of 1.95%, ending positive in 79% of cases.

What’s behind the rally? It’s not just Christmas spirit

So what exactly drives this December seasonal phenomenon? Part of the answer lies in fund managers’ behaviour.

Christoph Geyer, an analyst at Seasonax, believes the rally is closely tied to the behaviour of institutional investors. As the year draws to a close, many fund managers make final portfolio adjustments to lock in performance figures that will be reported to clients and shareholders.

This so-called “price maintenance” often leads to increased buying, especially of stocks that have already done well or are poised to benefit from short-term momentum.

This behavioural pattern gains importance in years when indices such as the DAX trade within a sideways range — as has been the case since May this year. A sideways market is one where asset prices fluctuate within a tight range, lacking a clear trend.

According to Geyer, a breakout from this sideways range for the DAX appears increasingly likely as December kicks in.

From mid-November to early January, historical patterns suggest a favourable outcome, with a ratio of 34 positive years versus 12 negative for the German index — and average gains exceeding 6% in the positive years.

While past performance does not guarantee future returns, December’s track record across major global and European indices provides a compelling narrative for investors.

In short, December’s strength is not just about festive optimism. It’s a convergence of seasonal statistics, institutional dynamics, and technical positioning.

Disclaimer: This information does not constitute financial advice, always do your own research to ensure investments are right for your specific circumstances. We are a journalistic website and aim to provide the best guidance from experts. If you rely on the information on this page, then you do so entirely at your own risk.