Tom Brady was born on August 3rd, 1977. In the Super Bowl, Brady’s Patriots defeated the Los Angeles Rams, who had two players — running back Todd Gurley and pass rusher Dante Fowler — who were born on August 3rd, 1994. Rookie defensive back and All-Pro Derwin James was born two years later, on August 3rd, 1996.

Those four were not picked at random: there were 12 players active in the NFL last season who were born on August 3rd, making it an extremely popular birthday in pro football circles. What’s more, there were 203 players who played in the NFL in 2018 who were born “around August 3rd” — i.e., within 15 days of either side of that date. For fans of astrogoloy, these are your Leos, natural born leaders described as “dramatic, creative, self-confident, dominant and extremely difficult to resist, able to achieve anything they want to in any area of life they commit to.”

In the abstract, knowing that 203 players were born in one 31-day window probably means nothing to you. But I did this same analysis for every day in the calendar year. Christian McCaffrey was born on June 7th, the only such player active last season. As it turns out, the 31 days including and surrounding June 7th (i.e., May 23rd through June 22nd) produced only 147 players.  These are your Gemini, who are generally thought to dislike repetition and routine. Oh, and that window just brings in June 22nd, notable for being the only day on the calendar where no 2018 NFL players were born.

The graph below shows each of the 365 days of the year on the X-Axis. ^[1]Eric Kendricks is the only February 29th birthday, and to make life simple, I included him with the March 1 birthdays The Y-Axis shows how many players were active in the NFL last season with birthdays plus or minus 15 days of each date. As you can see, Brady’s August 3rd birthday comes in the middle of an extremely popular window for NFL birthdays, while McCaffrey’s June 7th birthday is at the center of one of the graph’s valleys.

A couple of notes.  In this methodology, the windows surrounding early January birthdays bring in December birthdays, and late December birthdays bring in January birthdays. That’s appropriate if we are looking at 31-day periods, but it’s possible (probable?) that two people born on December 27 and December 30th have more in common than two people born on December 30th and January 2nd of the following year. We will deal with this issue in a future article.

Why did I choose 31 days? Looking at individual birthdays produces a jumbled mess due to the small sample size. There’s nothing weird about July 9th, but it’s a date when only one 2018 NFL player was born. Meanwhile, 6 players were born on July 8th and 8 players were born on each of July 10th, July 11th, and July 12th. I looked at 21-day periods, and while the results look a little different, it still feels choppy and more likely driven by randomness. But you can see for yourself.

But there is something else to consider when analyzing these birthday rates: late summer birthdays are very common. July birthdays are popular, August birthdays are really popular, and September is the most popular birth month. So while many NFL players having early August birthdays looks like an outlier, it looks like less of an outlier given that context.

I’ve reproduced the above graph, but this time, I am adding an orange line (plotted against the right Y-Axis) that shows the popularity of each 31-day birth window. This is expressed as a percentage relative to the average calendar date. For example, late December/early January provide the fewest amount of birthdays (about 96% of the average), while late September gives us the most common window (about 106% of average). When you plot these two sets of data together, the results become really interesting. The NFL player data is plotted on the left Y-Axis in blue, while the U.S. birth rate is in orange against the right Y-Axis.

All the sudden, late December, January, and early February birthdays don’t seem so bad.  These are your Capricorn and Aquarius babies that seem to make the NFL at disproportionately high rates.  Meanwhile, June babies really struggled to make it to the NFL in 2018.  There were just 145 players born in June in the NFL in 2018, the fewest of all months (October was second with 155, and May had the third-fewest at 158).  And that’s despite June being a very average month for birthdays overall.

Meanwhile, there were more 2018 NFL players born in January than any other month, and by a good margin.  An incredible 197 players were born in January, compared to 185, for the runner-up July.  That’s even more amazing when you consider that January is one of the least popular birth months.

Please leave your thoughts in the comments.