10 Most Common Birthdays In The World

Top 10 most common birthdays in the world. Photo: KnowInsiders

Knowing your due date means knowing a whole lot more than when you can expect your little one to arrive. It could determine anything and everything from the logistics around your labor and delivery to the time of year your child can expect to celebrate their birthday.

Curious if your kid on the way will be celebrating during the most common birthday month and therefore have plenty of classmates celebrating, as well? Or maybe they'll be born on the least common day of the year for babies to make their big entrance into the world? Now you can figure that out, thanks to a viral blog post from The Daily Viz's Matt Stiles.

Here's the scoop on the most common birthdays in the world:

The Most Common Birthdays

September 9

September 9 is the most common birth date on the planet, which has seen an average of 12,301 births from 1994 to 2004 in the United States alone. All the people born on September ninth are usually conceived on December 17 of the previous year.

September 19

Photo: Mental Floss

The second most common birthday is September 19. The United States recorded an average of 12,229 births on September 19 from 1994 to 2014. Theoretically, all the people who were born on September 19 were conceived on the day after Boxing Day in the previous year on December 27. The people born on the two most common birthdays on the planet were conceived during the holiday season in December.

September 12

The third most common birthday date in the world is September twelfth. According to the data from the National Center for Health Statistics, there was an average of 12,225 births in the United States from 1994 to 2014. Since the total gestation period of human beings is 38 weeks, most of the people born on September 12 were conceived on December 20, the previous year.

September 17

September 17 is the fourth most popular birthday date when an average of 12,148 individuals are born in the United States. People born on September 17 were conceived on Christmas day.

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The Most Common Birth Month

Using real birth data from the U.S. National Center for Health Statistics and U.S. Social Security Administration, gathered by FiveThirtyEight, which covers 20 years of American births, Stiles concluded that September is the most popular month to give birth to a child in the U.S. In fact, nine of the top 10 days to give birth fall between September 9 and September 20.

So, then, the question is of course, why?

"If you back up 38 weeks, that means many couples are conceiving in December and around the holidays," explains Whitney Casares, M.D., M.P.H., F.A.A.P, author of The New Baby Blueprint: Caring for You and Your Little One. "It makes sense that they may be more likely to conceive during more celebratory seasons."

Another reason, Dr. Casares points out: According to a study in Obstetrics and Gynecology, couples may have more luck conceiving during the winter season due to higher-quality sperm in winter versus summer months. "They also postulated that changes in daylight length might make an ovum’s environment better-suited for a sperm," she notes. "More research is needed to understand this interesting phenomenon.

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Why September Is the Most Popular Month for Birthdays

Photo: Pinterest

1. Winter is for lovers. Turn the great clock back 40 weeks from September 19 and you’ll find yourself in the December holiday season. As Stiles writes on his blog, “Following a customary gestation period, many of these babies [born on September 9th and 19th] would, in theory, have been conceived on Dec. 17 and 27, respectively.” This makes sense: Many American students and laborers take time off around Christmas, meaning couples have more time for vacation, relaxation, and, yes—baby-making. There is even some data to back this up: Statistically, more couples have sex on vacation.

To that end, Christmas and New Years are thought to be the least popular birthdays because would-be parents know that many doctors try to take holiday vacations of their own. As Mental Floss UK points out, “In the U.S., 10 percent of births were induced before 1990, and that figure almost doubled in the decade after.” As you can see from the data, the birthing lull on Christmas is followed by a spike right after. The conclusion we can draw is that more parents seem inclined to induce birth just before or after the winter holidays, not during them.

2. Our bodies crave winter cuddles. Beyond simply having more time to couple, our bodies may be biologically disposed to winter conceptions. In 2001, researchers at the University of Texas School of Medicine summarized the science community’s various theories: “Biologic hypotheses include deterioration of sperm quality during summer, seasonal differences in anterior pituitary-ovarian function caused by changes in the daylight length, and variation in quality of the ovum or endometrial receptivity. Increased sexual activity associated with end-of-year holiday festivities has also been postulated as a possible behavioral explanation for the December peak in conceptions. The exact reasons remain unknown.”

3. Every day is a popular birthday. Stiles notes that, while there is a clear peak in September, the actual differences in birth numbers between common and less common birthdays are often within just a few thousand babies. For example, September 19th, the second most common birthday of the year, has an average birth rate of 12,229 babies; Meanwhile, November 24th, the 356th most common birthday, has an average birth rate of 10,015 newborns. Save for the holiday outliers (Christmas day has a birth rate of just 6,574 babies), almost every day is a relatively common birthday.

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