How Many People Share Your Birthday?

By Sam McPherson

Our birthdays come around only once a year, and no matter how old we are on that day, it always is fun to be the center of attention for just a little while. Whatever may be challenging in our lives moves to the back burner, for at least a few moments, on the day of our birth.

Sharing that special limelight with someone can be both fun and frustrating, of course. Making memories with family and friends that share your birthday can be a very amazing and rewarding experience, but what about in the workplace? Having a communal birthday serenade with six people from different departments on different floors of your office building—coworkers you don’t know at all—isn’t as memorable.

Virgos Abound

Two major data sets in the last five decades give us a very good look at which days are the most common birth dates in the United States: The New York Times published Harvard University data from 1973-1999 back in 2006, and more recently, The Daily Viz website provided a clear look at birth information compiled by the U.S. National Center for Health Statistics (1994-2003) and the U.S. Social Security Administration (2004-2014).

In both sets of data, the middle of September produced the most-common birthdays in America. In the Harvard data, six of the 10 most popular birthdays fell between Sept. 9 and Sept. 18: The 16th day of the ninth month was the most-common day for birth from 1973-1999, followed by the ninth day of the ninth month. Other popular days in this range were Sept. 17 (fourth most common), Sept.15 (eighth), Sept.10 (ninth) and Sept. 18 (tenth).

The more recent numbers from the NCHS and USSSA echo these dates: Nine of the Top 10 birth dates fall between Sept. 9 and Sept. 20 in these data sets, with the ninth day of the ninth month leading the way. The 16th falls to ninth in this data, but only about 245 births on the average each year separate the top day (Sept. 9) from the 10th day (Sept. 18).

The Most Unpopular Birthdays

There no major holidays in the U.S. around this time of year, meaning the children born in this range often have the birthday attention all to themselves (if not a few classmates or coworkers, of course). That seems to be one of the factors in identifying the least-common days for birth, according to the data, since Jan. 1 and Dec. 25 are consistently the most unpopular birth dates.

This trend would indicate a lot of couples/parents plan the birthdays of their children accordingly, to avoid conflict with holidays. Of course, not all pregnancies are planned, but the data collected from 1973-2014 in these studies definitely demonstrates a pattern worth recognizing: The most common birthdays are in the middle of September.

The Reason for the Autumnal Uptick?

With 38 weeks being the average time between conception and birth, this means a lot of people are conceiving right around Christmas Day—an aforementioned “unpopular” time for childbirth. Perhaps for couples, then, there is no better gift in the wintry, holiday season than news of an expected addition to the family in the upcoming new year.

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