Pretty Much Everyone Is Celebrating a Birthday This Week

A Harvard economist's data finds particular relevance in mid-September.

Happy birthday! It’s your special day!

Hm, what’s that? You were born on September 23? Okay, maybe it’s not that special. Some birthdays are more common than others. And September, traditionally, marks a real baby boom.

Back in 2006, Harvard economist Amitabh Chandra provided the New York Times with data on births between 1973 to 1999 in the United States. His research often makes a resurgence around this time of year, and no wonder. It reveals September 16 to be the most popular birthday in America. And in fact, the 10 most popular birthdays all fell between September 9 and September 24.

Why is that? Subtract 38 weeks from these days and you get the weird realization that a lot of people are getting down and dirty right around the holidays. Put September 16—the most popular birthday in America—into a conception date calculator and you get December 24. (It appears that Mommy did a little more than kiss Santa Claus.) Put September 23, the third most popular day, into the calculator, and you get December 31.

The Times found that this is beginning to change, though. As C-sections and induced births give people more choice over the day their baby is born, December is becoming a more popular month to birth a kid. Why? The Times’s David Leonhardt had a theory:

Over this same period — since the early 1990s — the federal government has been steadily increasing the tax breaks for having a child. For parents to claim the full amount of any of these breaks in a given year, a child must simply be born by 11:59 p.m. on Dec. 31. If the baby arrives a few minutes later, the parents are often more than a thousand dollars poorer.

Basically, a cynical reader of the data can assume that people who are due to have a baby right around the new year choose to schedule the birth a few days early to get access to the tax breaks. The holidays are appealing for other reasons, too. There’s more family around, and people have more vacation.

So while September is unrivaled as a pretty unoriginal time to be born among a certain generation, the young folk are going to have a lot more birthday parties to get to during the holiday season. Those 15 and older, though, should prepare to write on a lot of Facebook walls this week.