The casting of Blake Lively and Justin Baldoni as Lily and Ryle caused backlash from fans because in the book, Lily is 23 and Ryle is 30, while Lively is 35 and Baldoni is 39. Author Colleen Hoover explained in an interview that she wanted to age the characters up in the movie to correct a mistake she made in the book. She said, "Back when I wrote It Ends With Us, the new adult [genre] was very popular. You were writing college-age characters. That's what I was contracted to do. I made Lily very young. I didn't know neurosurgeons went to school for 6-12 years. There's not a 20-something neurosurgeon. As I started making this movie, I was like, 'We need to age them out because I messed up.' So, that's my fault."
Young Lily's actress Isabela Ferrer's facial mole, in the same place as Blake Lively's, is natural, not a prosthetic.
While the film is based in Boston, it was filmed in New Jersey, primarily in Hoboken and Jersey City.
The name of Atlas's restaurant has been changed. In the book, it is BIBs (short for "Better in Boston"), but in the movie, it's been changed to "Root."
Blake Lively's sister Robyn Lively & Justin Baldoni's wife Emily Baldoni have small roles in this film.