On what date is Festivus celebrated in Seinfeld?

In Seinfeld, Festivus is celebrated on December 23.

The date is established in season 9’s “The Strike,” the 1997 episode that brought Festivus into mainstream popular culture. Frank Costanza presents it as an alternative to the commercial pressures of Christmas. The celebration includes a Festivus dinner, an unadorned aluminum pole, the airing of grievances, feats of strength, and declarations of “Festivus miracles.”

The episode first aired on December 18, 1997, but the holiday itself occurs five days later, on December 23. That distinction causes a common mix-up: the broadcast date is not the fictional holiday’s date.

Festivus was based on a real family tradition created by writer Dan O’Keefe’s father, Daniel. The real-life version had no fixed date and used a clock in a bag rather than an aluminum pole. The fixed December 23 date and pole were elements developed for the Seinfeld story, where Frank declares it a holiday “for the rest of us.”