Thursday, September 2, 2021

Happy Birthday!

It is hard to believe that September is already here.

September is also the month that I have the best chance of wishing you "Happy Birthday" and being right.

A study of all births in the United States between 1994 and 2014 showed that September was the most popular birth month.

In fact, September has nine of the top ten birthdays for the entire  year. Those nine days are actually all between September 9 and September 20.

If you turn back the clock 40 weeks you can also determine that mid-December would also be a popular period for conceptions to occur. Is it the cold weather or the holiday mood?


September 9 was the most popular birthday in the study followed by September 19 and September 12.

The least common days to be born are all holidays: December 25 is the least common followed by January 1, December 24 and July 4. This suggests to me that nature has been overriden by either a doctor who has other plans for the holiday or a family who does not like the idea of having their child's birthday overshadowed by other events.

Notice in the chart above the spike in births on December 28, 29 and 30? That might suggest some tax planning is also in play as well.

That might be true even more so in 2021 with a $3,600 refundable tax credit available for every child age 5 and under. Will there be any children born in the first week of January, 2022?

What about the most popular birthdays in other countries?

Let's look at Australia in the Southern Hemisphere.

December is in their summer season. July is in their winter. You might expect a different pattern on births if seasonality is a driving factor.

Curiously, the most popular birthday in Australia is September 17. September 23, 24 and October 1 are also in the top 5. It might suggest that the feelings of the holiday season has more influence than climate in conception.


The least popular birthdays in Australia are December 25 and December 26 (Boxing Day which is a holiday in Australia).

Note that there is no surge in births in Australia in the last week of the year. No strong tax incentive?

You can also see that February, March, April do have a fairly high percentage of the most popular birthdays in Australia. Backing up nine months gives us May, June, July which are cooler climes Downunder. In fact, April 8 is the second most popular birthday and the only one in the Top 5 that does not correspond to conception in the holiday season.

In the United Kingdom September is also the most popular birthday month according to a study of all births from 1995-2017.

The five most popular birthday are all in late September in this order.

September 26

September 25

September 24

September 27

September 30

Nine months before? Christmas and Boxing Day (December 26).

Despite the differences in the charts above, the numerical differences between the most popular birthdays and least popular are not as great as you might be led to believe.

For example in the UK, the most popular day, September 26, sees an average of 1,974 births in the average year. There were still 1,422 births on Christmas Day. 

The same is true in the U.S. and Australia. You generally will only see a variation of 20%-25% between the most popular and least common birthdays. Nature still is (mostly) in control.

Happy Birthday no matter when the big day is!

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