On Harry Potter Wiki it classifies the books by the year they are supposed to take place in. The first book which was released in 1997 is said to take place in 1991, but how was this decided?? Can someone please explain why the books take place from 1991 to 1998 and how this came to be?
Since Harry was born on July 31st, 1980, the books have to start in 1991, since that is when he would have been 11 years old.
In the second book,chamber of secrets, Harry,Ron,and Hermione go to the death day party. It is mentioned that it is Nearly headless Nick's 500th death day, honoring his October 31,1492 death day. 500 years after 1492 is 1992, and Harry's first year at hogwarts is 1991-92 a's his second is 1992-93, third 1993-94...... You get the picture.