How Dangerous Is The Month Of October?

A Month with a Bad Reputation

A certain degree of nervousness tends to suffuse global financial markets when the month of October approaches. The memories of sharp slumps that happened in this month in the past – often wiping out the profits of an entire year in a single day – are apt to induce fear. However, if one disregards outliers such as 1987 or 2008, October generally delivers an acceptable performance.

The road to October… not much happens at first – until it does. [PT]

Nevertheless, the prospect of such an extremely strong decline is scary: what use is it to anyone if markets typically perform well in October most of the time, whenthe phenomenon of the gains of an entire year evaporating in the blink of an eye is repeated? What about intermittent losses? We will apply seasonal analysis to the issue in order to shed light on whether one should adopt a risk-averse stance in October.

The Biggest Crashes Tend to Happen in October

Let us take a look at the largest declines in recent history. The following chart shows the twenty largest one-day declines in the Dow Jones Industrial Average. Crashes that occurred in October are highlighted in red.

The largest one-day declines in the DJIA in history – almost half of the crash waves occurred in October,including the two largest ever recorded on 19 Oct. 1987 and 28 Oct. 1929. The fourth largest decline happened on 29 Oct. 1929 hence these two days of consecutive declines were actually worse than the record one-day plunge in 1987 (similar to 1987, the market had already fallen sharply in the week immediately preceding the crash). [PT]

9 of the 20 strongest one-day declines happened in October. That is an extremely disproportionate frequency. In other words, October has a strong tendency to deliver negative surprises to stock market investors in the form of sudden crashes. What does this mean for us as investors?

What to Make of Exceptionally Large Gains?

First of all, the first half of the year appears to be much safer from sudden declines. Only two of the 20 largest one-day losses happened in these six months.