The film is presented in a nonlinear narrative, this summary is a linear version of the events of the film


On January 8, Tom Hanson (Joseph Gordon-Levitt) meets Summer Finn (Zooey Deschanel), the new assistant to his boss (Clark Gregg). Tom trained as an architect but works as a writer at a greeting card company.


One month later following a karaoke night Tom's co-worker, McKenzie (Geoffrey Arend), lets slip that Tom is attracted to Summer. Over the next few months Summer and Tom grow closer, despite Summer making it clear to Tom that she does not believe in true love, and does not want a boyfriend.


Tom shows Summer his favorite spot in the city, which looks out over a number of buildings he likes, although the view is spoiled by car parks. After a few weeks dating Tom gets into a fight with a guy chatting up Summer, and they have their first argument.


On day 290 Summer and Tom split up after they see The Graduate, a film which Tom thinks shows true love. Tom does not take the break up well and Tom's friends call his younger sister, Rachel (Chloë Moretz), to calm him down.


Summer quits the greeting card company and Tom's boss moves him to consolations, as his depression is not suitable for happier events.


Months later Summer and Tom attend the wedding of a co-worker, they dance at the wedding and Summer catches the bouquet. They sit next to each other on the journey home and Summer invites Tom to a party at her apartment for the Friday. Tom attends the party and sees that Summer is wearing an engagement ring. Realising what is being celebrated, he leaves the party.


Tom enters a deep depression only leaving the house for alcohol and junk food. After a few days he returns to work, drunk, and quits his job. He sets about re-applying himself to architecture and makes a list of firms, and begins to attend interviews.


On day 488 he meets Summer at his favorite spot and they reconcile, he wishes her well. Twelve days later he attends a job interview and meets a girl (Minka Kelly), who is also going for the same job. Before entering the interview he makes a date to have coffee with her afterward. He asks her for her name, and she replies "Autumn."