Market timing does not work (1). However, there are still plenty of investors who believe in market timing, and a subset of these believe that January Effect and October Effect are real. In a true MythBusters‘ fashion, I did some historical data analysis and have a few statistical factoids to share with you. But first…
Some people believe that stock prices generally increase during the month of January, because people are buying back stocks after end of the year sell-off by investors harvesting tax losses.
There’s a theory that stocks tend to decline in October, because it’s cursed. Coincidentally, the dates of some large historical market crashes occurred during this month — for example, Panic of 1907, Wall Street Crash of 1929, and Black Monday, October 19, 1987.
You can skip this table if it gives you migraine.
The table above shows us monthly performance of the S&P 500 for the past 30 years:
Even if you’re sure you see an unmistakable trend, don’t bet the farm on it, because other people sees it too. The efficient market hypothesis dictates that you can’t take advantage of any such trend. For instance, after reading this post you (and everyone else) think August is the best time to invest, then next year people will anticipate the sharp gain in August and invest in July instead, and so on and so forth…
Note: (1) There are a few exceptions of timing that work — e.g., tax-loss harvesting and timing mutual fund buys to avoid capital gains distributions.