Fans of the series know that the star of the franchise celebrates --- or perhaps more accurately, is ignored on --- his birthday every summer in the books, often while he's with his aunt, uncle and cousin, who generally dislike him. Harry was born on July 31, 1980. The significance of this date is that author JK Rowling's birthday is July 31 as well.
Harry's best friend Ron is a few months older than Harry. Readers of "Harry Potter and the Half Blood Prince" will remember Ron taking his apparation test at age 17 before Harry is eligible. Ron's date of birth is March 1, 1980. Ron is the second-to-youngest child in the Weasley family and is almost a year-and-a-half older than his younger sister Ginny, who was born on Aug. 11, 1981.
The only Muggle-born witch among the series' main trio of characters, Hermione is also the oldest of the three. Her date of birth is Sept. 19, 1979. However, you may note that some sources quote her birthday as Sept. 19, 1980. This is an error, because details in the books, such as the apparation test in "Harry Potter and the Half Blood Prince," suggest that Hermione is older than both Ron and Harry.
Harry's mentor and the headmaster of Hogwarts never reveals his exact birth date. However, JK Rowling made statements that he was about 150 years old during "Harry Potter and the Sorcerer's Stone." Couple this with some details from the flashbacks to his youth --- he was nearing 18 years of age after his graduation from Hogwarts --- and you can determine that his birthday is likely sometime in July or August and he was probably born around 1881.
Harry's cruel teacher Professor Snape is an enigmatic figure in the series who never quite reveals his true allegiances to the good or evil side of the battle until the very end. His birthday is Jan. 9, according to JK Rowling. The year in which he was born was most likely 1960. This year is taken from the fact that Harry's parents' graves reveal their birth years in "Harry Potter and the Deathly Hallows," and they were in the same year at school as Snape.