Leap Day Birthdays

Published by patrick honner on

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!

Leave a Reply

Your email address will not be published. Required fields are marked *


Get every new post delivered to your Inbox

Join other followers: