Seasonality refers to the time frames when stocks, sectors, indexes, and markets are influenced by recurring tendencies. The historical patterns tend to be apparent and remain consistent over an extended period. The key is the recurring tendencies and the sustainable probability of performing in a manner consistent with previous results.
So, what does the seasonality say about December?
On the stock market front, December generates consistent positive gains for US market indexes. For instance, the S&P 500 Index (SPX) is up 70% of the time, with average gains of 0.6% over the past 20-years. Dow Jones Industrial Average (INDU) has increased 65% of the time and average gains of 0.7% over the past 20-years. Nasdaq Composite Index (COMPQ) closed higher 60% of the time with average gains of 0.3%. The Small-cap 600 Index (SML) closed higher than it opened 65% of the time, with average gains of 1.2%. The Mid-cap 400 Index also recorded a higher close 70% of the time, with average gains of 1.1%.
On the sector front, December is generally favorable for the 11 S&P 500 sectors with positive gains over the past 20-years. Only one S&P 500 sector showed negative returns during December. The December average returns ranked by the S&P 500 sectors are as follows: XLRE (70% higher and 3.2% return), XLC (71% and 1.8%), XLU (70% and 1.4%), XLV (70% and 1.1%), XLE (60% and 1.1%), XLF (75% and 1.0%), XLB (60% and 0.9%), XLI (60% and 0.8%), XLY (75% and 0.7%), XLP (60% and 0.4%), and XLK (55% and -0.1%).
In summary, December is a strong seasonal month for US stocks. In the past 20-years, key US stock indexes return positive average gains during the month. The higher beta small-cap and mid-cap markets are typically strong into the end of the year, outperforming their larger-cap counterparts with average gains of 1.2% and 1.1%, respectively. Surprisingly, despite the positive average return during December technology-laden Nasdaq Composite Index (0.3% average return) has relatively underperformed SPX (0.6%) and INDU (0.7%). December is also a strong month for most of the S&P 500 sectors with one exception - XLK is the only S&P 500 sector with negative returns (-0.1%).
It is also interesting to note the best December performances came from many of the defensive sectors such as XLRE (3.2%), XLU (1.4%), and XLV (1.1%). Before the rebalancing of the S&P 500 communication sector (XLC) was an income and defensive related sector. However, with the reshuffled on 9/21/18, XLC is a more diverse sector comprised of traditional telecommunication names, and technology-related tech giants as well as large consumer discretionary companies. Although XLC remains the second-best performing S&P sector based on the December average gains of 1.8% over the past 20-years this sector may excel into the end of the year as XLC underperformed last month but has recently confirmed new all-time highs with relative strength improving into the recent rally.
The stock market recorded a historic November rally with some of the largest monthly gain on record for the small-cap markets and big advances for other major US indexes. The recent rising bullish sentiments are the expectations of the COVID-19 vaccine treatments gaining final FDA approvals as early as year-end. And while December is historically a strong month for equities and S&P sectors, traders and investors need to be prepared for an increase in volatility in the coming weeks as some of the laggards may defy historical seasonality tendencies and shine in the coming weeks while the historical December leaders take a breather by consolidating their November gains.