# Dating someone with the same birthday as you

*22-May-2015 12:28*

Twenty nine of us meeting someone with the same birthday: 1/12.

Those are pretty good odds, but not high enough to account for all those coincidences. The odds are actually much higher (over 100 percent for a class of 30).

Then they discovered that their wives also shared a birthday (different than their husbands).

“After thinking about how to calculate the odds, we concluded the best approach would be to contact you,” Mr.

Numbers Guy reader Ira Akselrad recently heard an improbable tale.

His colleague met someone who was born the same day and month.

Four people (lets call them ABCD) have a 1/91 chance, but there are 6 possible combinations (AB AC AD BD BC CD) so the probability becomes 1/91 + 6/365…and so on.

Two people have a 1/183 chance of meeting someone with the same birthday. Those two people might also have the same birthday, right, so you have to add odds of 1/365 for that.

Same Birthday Odds It stands to reason that same birthday odds for one person meeting another are 1/365 (365 days in the year and your birthday is on one of them).

But consider this: If you get a group of 30 people together, two of them will almost definitely have the same birthday. There were 30 students in my undergrad statistics class and the professor said the odds of two of us having the same birthday were very high. We’re talking about every student having those odds.

The reason takes into account all of the possible combinations.

One person has a 1/365 chance of meeting someone with the same birthday.

It’s like if I had a 1/10 chance of winning the lottery and I meet another person who also has a 1/10 chance of winning the lottery, then combined we have a 2/10 chance of winning the lottery.The odds of a “coincidence” increases with each person: Me meeting a person with the same birthday: 1/365 Me and one other friend meeting someone with the same birthday: 1/(365/2) = 183 Three of us meeting someone with the same birthday: 1/(365/3) = 1/122 …