Birthdays are either a day filled with fun, friends, and family or a day of unbridled angst and insecurity usually brought on by friends and family. We all have a birthday and there's a better-than-average chance that you share yours with a couple of million other people around the world.

In fact, the birthday paradox suggests that if you're in a room with 23 people, there is a 50% probability that at least two people will share the same birthday. I know it seems hard to believe but when you do the math, we didn't but these folks did, and the numbers add up.

Maybe this is just pure coincidence but in my family, almost all of the birthdays are clustered within just a few weeks. My brother, my sister, and my mom all share a birthday that's within five weeks of mine. But, when you do the math, sorry to keep bringing math into this, it's pretty easy to see why so many birthdays happen in the early fall.

If you did some snooping in the records section of the Centers for Disease Control and the Social Security Administration you would know that the most common birthday in the United States is September 9th. The next two most common birthdays in America are September 19th and September 12th.

### Why Do So Many People Celebrate a Birthday in September?

The answer should be pretty obvious if you count backward for forty weeks. Forty weeks is about how long it takes for a human woman to give birth after becoming pregnant. Forty weeks back from September puts us right smack dab in the middle of the holiday season.

So, obviously, people are doing things other than just kissing under that mistletoe. Demographers are unsure if "it's the holiday magic", the "high-proof" egg nog, or if it's simply the fact that most people get to take personal time off during the holiday season and we all know what happens when that happens.

But oddly enough, September isn't the most popular month for births, that distinction goes to August according to the CDC. July is the second most common month for births while September comes in at number three and October at number four. As you might imagine, February is the least common month for a child to be born.

By the way, if you're wondering what day is the day you'd be least likely to share a birthday with someone, the answer to that is December 25th, yep Christmas Day. Part of the reason for that stat could be the fact that parents who have to schedule a C-Section aren't going to do that on Christmas.

## LOOK: Food history from the year you were born

From product innovations to major recalls, Stacker researched what happened in food history every year since 1921, according to news and government sources.