13 September is the 256th day of the year (257th in leap years). There are 109 days remaining.
- 1991: Shortly after midnight, Harry Potter, Ron Weasley, Hermione Granger, and Neville Longbottom avoid Argus Filch, who was tipped off by Draco Malfoy that the Gryffindors were out of bed. While running from him in the third floor, they discover Fluffy the three-headed dog in the Forbidden Corridor.
- 1995: Harry Potter serves his last detention with Dolores Umbridge's detention quill.
- 1996: Stan Shunpike is accused of being a Death Eater, arrested, and taken to Azkaban.