# Leap Day Birthdays

In my Leap Day contribution to the New York Times Learning Network, “10 Activities for Learning About Leap Year and Other Calendar Oddities,” I calculated the odds of a person having a Leap Day birthday.

Assuming each day of the year is an equally likely birthday, and noting that there is one Leap Day every four calendar years, I calculated the probability to be

(Leap Day Birthday) = $\frac{1}{4*365 + 1} = \frac{1}{1461} \approx 0.0068$

or around 0.7%.

So how many people with Leap Year birthdays do you know?

#### patrick honner

Math teacher in Brooklyn, New York

#### ihor · March 1, 2012 at 5:03 pm

This reminds me of the classic birthday problem where you need only 23 people in a room for there to be about a 50% chance of a match. So how big a stadium, country or continent do you need in order to have enough room for the number of people you need to get a 50% chance of sharing a leap birthday? Hmmm let me think about that one. 🙂
Great website!

#### MrHonner · March 1, 2012 at 7:10 pm

I also was thinking about how the classic birthday problem fits in with rarity of the the leap-day birthday. And then I saw this story about a mother and daughter who were both born on leap day!

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