text: firstly, you are not dumb as the idiot above says so!\n\nyou have got a very good question there, i have been wondering the same. there it was in the third book that hermoine says that it was her birthday in spetember and her parents gave her 10 galleons to buy anything she wants.\nher excat birthday date is not mentioned in the book nor in movies. but i guess JK rowling told it and it got published on internet sites.