This week, several media outlets rediscovered an old New York Times chart that tells you how popular your birthday is, ranking each day of the year from 1 to 366. While it's fun to learn the most common birthdays in the U.S., it's much more fun to think about the most popular conception dates! As it turns out, they aren't at all random. The most common birthday in the United States, according to the Times data, is September 16, and the average pregnancy lasts 38 weeks, so using Discovery Health's handy conception calculator, we discovered that the most popular conception date is December 24! That's according to the typical method for estimating due dates anyway. But if the logic follows, more Americans fertilize an egg on Christmas Eve than on any other day of the year. (Disturbing news for those 9/16 babies who would prefer not to know that their parents probably created them in an in-law's guest bed.)
But there's more: The third most popular birthday in America is September 23. Subtract the length of a pregnancy, and lo and behold, you get December 31 -- New Year's Eve! The third most popular conception date. Calculating conception dates is obviously tricky business because pregnancy lengths vary. But in general, when you consider that the top 10 most common birthdays all fall between September 9 (the second most popular, which would have a conception date of December 17) and September 24, it would seem that the holiday season is a busy, busy one for American parents-to-be.