Lost produced six seasons.
The American television series premiered on ABC on September 22, 2004, and concluded with its sixth and final season on May 23, 2010. Across those six seasons, Lost released 121 episodes about the survivors of Oceanic Airlines Flight 815 and the island’s increasingly complex mysteries.
The show’s planned ending was publicly announced in 2007, allowing the producers to shape the remaining story toward a definite conclusion instead of continuing indefinitely. The final 48 episodes were originally planned as three 16-episode seasons, but production changes and the Writers Guild of America strike affected the episode counts. The sixth season ultimately contained 18 episodes.
A frequent counting mistake comes from treating the three planned final blocks as three separate seasons, which would suggest seven seasons overall. That was not how the series aired: Lost ended after season six, with the finale “The End” closing the main storyline.