Ben Affleck postponed directing Live by Night (2016) in order to work on this film with David Fincher, even stating, "He's the only director I've met who can do everybody else's job better than they could." On-set one day, Affleck changed the lens setting on a camera an almost indiscernible amount, betting a crew member that Fincher wouldn't notice. Affleck lost the bet as Fincher brought up, "Why does the camera look a little dim?"
David Fincher explained that one of the reasons he cast 35-year-old Rosamund Pike as Amy was that she was of unclear age in her appearance, and could pass for an older or younger woman. Rosamund's revelation that she was an only child also proved to be a very appealing aspect for Amy's character in Fincher's opinion.
"The Bar" restaurant in the movie opened as a functional bar and restaurant after filming and operated for a few years. It has since permanently closed.
Reese Witherspoon obtained the film rights from Gillian Flynn in June 2012, and decided to produce under her new production label "Pacific Standard" as she would be able to play the role of Amy. However, after her initial meeting with David Fincher on his vision of the film, Witherspoon withdrew from contention, realizing that she wasn't the right person to play the female lead.
Ben Affleck's weight fluctuates in the film with him being of fairly average build, to being muscular, as a result of being cast as Batman in Batman v Superman: Dawn of Justice (2016).