Continuity mistake: Tom receives an e-mail from Summer on day (303). At the beginning of the movie we are told that Tom and Summer met on January 8, so day 303 should be November the 6th, but the e-mail says that it was sent on May 7th, which is day 120.
500 Days of Summer (2009)
1 continuity mistake - chronological order
Directed by: Marc Webb
Starring: Joseph Gordon-Levitt, Zooey Deschanel, Chloe Grace Moretz, Clark Gregg
Continuity mistake: Tom receives an e-mail from Summer on day (303). At the beginning of the movie we are told that Tom and Summer met on January 8, so day 303 should be November the 6th, but the e-mail says that it was sent on May 7th, which is day 120.
Tom: Did you ever do this, you think back on all the times you've had with someone and you just replay it in your head over and over again and you look for those first signs of trouble?