For the vast majority of individuals on the planet, about 0.27 percent of the world's population shares their birthday. There is an equal chance of anyone being born on any day of the year. So the odds of someone sharing your birthday are 1 in 365.
There is an important exception to the 1 in 365 chance rule. If someone's birthday falls on Feb. 29, the odds are not the same because this date occurs only once every four years. For those born on Feb. 29, the odds of a person being born on the same day are 1/1461 or 0.068 percent.