Dating someone with your same birthday
That's my ex's birthday, and he didn't seem too upset about having it that day.
He did at first, like you seem to have, but now he just doesn't seem to care, and says it's the only way he can remember it.
As has been noted, both the shared year and shared birthday probabilities could be further refined based on additional information.
When it comes to two people, there are many potential sources of coincidences. Within the domain of date of births, you could imagine many possible similarities: same month; same day of month; same star sign; same birthday, different year; some similarity in the numbers such as 2nd of May and 5th of February; dates are some round number apart (e.g., 8th of May 18th of May); dates are only only some small number apart (e.g., 8th and 9th of May).
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). 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? However, post hoc (that is, while in the relationship) it's trickier because you would have noticed a lot of coincidences too: My boyfriend was born the day before me!
My boyfriend's mother has the same name as my mother! The odds of "some weird connection with my boyfriend" are impossible to calculate.
Next one should figure out what the chance is of being born in the same year.
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.
Then, something the other didn't take into account, looking at birth rates per month we get a nice overview (it's caused by things like people being off thus having a lot of free time on hand 9 months before the months in question), next dividing that percentage by the number of days in that month.
For example, we could look at similarities in names, employment history, appearance, etc.
The larger you cast the search, the more possible bases there are for finding coincidences.
It's the chance of SOMEONE sharing a bday with SOMEONE else. Think of it, not as the number of people, but as the number of PAIRS you can make, which is (22 21 20 19..... Then do some complicated math.... OT: I wouldn't care if some1 shared my bday. I probably have the worst date for a birthday ever. I admit I actually did feel that way for the first year or so, but life goes on and there are alot worse things then having a sucky birthday. Yeah its probably not the greatest to have your birthday on a major party holiday like New Year's Eve or Christmas, but of all the not so great things that can happen to a person, having a "bad" birthday is pretty far down on the list. Get depressed and feel sorry for myself every year because the terrorists ruined my birthday?
Every year I would have to put up with her either getting depressed or throwing a tantrum because none of her friends seemed to care 'enough' about her cos NYE was always sealing her thunder. Yeah its probably not the greatest to have your birthday on a major party holiday like New Year's Eve or Christmas, but of all the not so great things that can happen to a person, having a "bad" birthday is pretty far down on the list. Get depressed and feel sorry for myself every year because the terrorists ruined my birthday?