Two Birthdays and One Anniversary On The Same Day

Special days don't get much bigger than August 26th at the Brainard house. The day is the birthday of our first child, Chase. It is ALSO the birthday of our second child, Carly. No, they aren't twins. They were born on the same day of the year, four years apart. As you might imagine, sharing a birthday with a sibling was cool when they were little kids. But now that they are both teenagers, it takes a bit more planning to make sure each of them feels like today is their own special day. Whenever I tell people that two of my kids share a birthday, the most common phrase I hear is "what are the odds of that"? Let's find out!

First of all a warning. Reading past this point will involve math and probability. In doing research the past several days on the commonality of birthdays, I stumbled onto a theory called The Birthday Paradox. It looks at the probability that two people in a random group could have the same birthday. But the math also works out when using it to find the odds of just two people sharing the same birthday. First, here is the equation used to find the odds.

Ok, now the explanation. Person 1, or my son Chase, can be born on any day of the year since he is the first person being born. The probability of being born on any day of the year is 1, or 365/365. Since person 2, or Carly, has to be born on the same day as Chase, their probability is 1/365. Since you want both events to happen, you simply multiply them together and you get the odds! There is a .27% chance that two random people will be born on the exact same day.

But what are the odds for siblings? Chase and Carly aren't two random people. Some say the odds are nearly 1 in 50,000 when it comes to that. I haven't located that math problem yet. In addition to the kid's birthdays, August 26th is also my parents, Steve and Nancy Brainard's 50th wedding anniversary! I'm so blessed to have them as parents and can't wait to celebrate with them this weekend!

What a party it will be this weekend! A 50th anniversary, Chase turning 18 and Carly turning 14!