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. We've argued before about the probabilities and I am still not satisfied. My point was that the chances are tiny if you consider the probabilities of being in a relationship (+ being successful at it for X amount of time). I find the amount of factors to take into account quite vast (up to a point, gender and age, availability, probabilities of separation in our region, etc.)
Is it even possible to calculate the probabilities on something like this? How would you go about it?
Best Answer
For any one relationship, the odds of sharing the same month and day are approximately 1 in 365 (not exactly because of leap year and because births are not exactly evenly spaced within a year. If you add in year, it's probably something like 1 in 3000 or 4000 (most people have relationships with people relatively close in age).
But that' a priori.
That is, if you had asked, before meeting your current boyfriend "What are the odds that the next man I have a relationship with will be born on same day and year?" the odds would have been 1 in 3000 or so.
However, post hoc (that is, while in the relationship) it's trickier because you would have noticed a lot of other coincidences too: My boyfriend was born the day before me! My boyfriend's mother has the same name as my mother!" etc etc.
The odds of "some weird connection with my boyfriend" are impossible to calculate.