Dating someone with the same birthday Chatroom for horny guys
I'd guess that P(same year) is roughly of the order of 0.1 to 0.2, but that's just a guess.
[Edit: Jeromy gives a figure based on actual data, which turns out to be about 17%.] According to wikipedia, 33.2% of married couples in the United States differ in age by less than one year.
But of course, when we speak about coincidences there is a much wide domain of search.
For example, we could look at similarities in names, employment history, appearance, etc.
If there were 30 people in your relationship then you'd expect two of them to share a birthday but there aren't 30 people, there are only 2.
Your question got me thinking, and I realized my girlfriend and I also have a strange birthday coincidence. So, first of all, the odds of sharing some weird connection with any random person are probably quite high.
From experience I'd guess around 20% or so, no way to seriously calculate that, but no matter what it exactly is, just want to be clear having a special weird connection means nothing (though it is fun).
I share the same birthdate as my boyfriend, same date but also same year, our births are seperated by merely 5 hours or so.
I know that the chances of meeting someone who was born on the same date than me is fairly high and I know a few people with whom I share my birthday although for the little I've read about the birthday paradox, it doesn't take same year into account.
Just to give an impression of this chance I'd start with the rule of thumb as presented by xkcd which gives a dating age range of $\pm \ age-\frac 7$, where age $=$ age you started dating. However, the chances of dating someone from the exact same year are far greater due to a flaw in the educational system where pooling is done by the date of conception.