How many non multiple birth siblings share birthdays?

[Lockon Stratos]

I've always wondered how many people, who don't have a twin or are a triplet or so on and so forth, share their birthdays or have a birthday extremely close to that of another sibling. My little brother is exactly 2 years and 363 days younger than me, so we've always used the dater inbetween our birthdays as the date for things such as parties and whatnot.
I'd like to know if anyone else has a situation similar to this.