Sell in May and come back…when?

The old saying goes “sell in May”.

But if you sell in May when should you come back into the market?

Well, in its original form the adage was, “sell in May and go away, don’t come back till St Leger Day”. And St Leger is the last big event of the UK horse-racing calendar, and usually takes place in mid-September.

A complementary anomaly (most likely originating in the US) is the Halloween Effect, which holds that stocks see the bulk of their gains in the six-month period 31 October to 1 May.

At some point it seems the sell in May saying and the Halloween Effect merged to become one. Such that today the sell in May adage is usually taken to mean that the summer period of (relatively) poor returns ends 31 October.

So, so far we have possible entries back into the market of mid-September or end October.

What does the recent data say?

The following chart shows the annual trend of the FTSE 100 Index calculated on data from 1984. (More information on this chart can be found here.)

Santa Rally [2015] 04

The chart illustrates fairly clearly the different nature of the two six-month periods:

  • 1 May – 31 October (Summer period): when the six-month return tends to be flat, and
  • 1 November – 30 April (Winter period): when the market tends to rise.

The data does support the claim that the greater part the market’s gains come in the Winter period.

Over the whole six-month Summer period the market doesn’t necessarily fall, but it does tend to be flat, and certainly the returns are less than in the Winter period.

However, it can be seen in the chart that the market is absolutely weak for the two-month period May to June.

So, according to the data since 1984, if you do sell in May, one time for coming back into the market would be the end of June.


More articles on the Sell in May Effect.

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