Frank tells Donnie the world will end in 28 days 06 hours 42 minutes and 12 seconds. The movie was shot in 28 days, which is exactly the time-span of the movie itself. Also There are 28 scenes in the director's cut of the film.
Donnie's mother and sister fly home from Sparkle Motion's Star Search performance on a red-eye flight. The Flight number of the plane is 2806 which boards at gate 42 and leaves at 12 AM. This is a reference to the 28:06:42:12 countdown that Frank gives Donnie.
Richard Kelly originally chose Donnie and Gretchen to go and see the movie C.H.U.D. (1984) in the theatre scene. There were problems with finding who owned the rights to this movie so it couldn't be used. Sam Raimi came to the rescue by allowing Kelly to use and distort footage from The Evil Dead (1981), free of charge.
The original poster art for the movie had been using an Arabic-style font, but this was changed to the much more standard Times New Roman boldface font for the video release after the terrorist attacks on the USA of 11 September 2001. The title remains in the same style in the film, though.
Noah Wyle decided that his character, Prof. Kenneth Monnitoff, would be diabetic and therefore is often seen eating candy. He is eating candy at the meeting after the school gets flooded and when Donnie and Gretchen give there IMG baby glasses presentation in school.
The shot of the bike ride to Grandma Death's house is an homage to Steven Spielberg's E.T.: The Extra-Terrestrial (1982), in which, Drew Barrymore also starred.
The movie takes place in 1988.
The world ends in 28 days, 06 hours, 42 minutes, and 12 secs.
If you add these numbers, the sum is 88.
When Samantha asks when she can have kids, Donnie says: "Not until 8th grade."
Donnie mentions to his therapist his dog died when he was eight.
According to the television reporter, the fire at Jim Cunningham's house was extinguished "sometime after 8:00 last night.".
Donnie mentions the DeLorean car, which was used for time travel in Back to the Future (1985).
In Back To The Future the DeLorean had to reach a speed of 88 mph to travel in time.
According to the commentary by Richard Kelly, the Man in the Red Jogging Suit is an agent from the FAA, which was so confused by the jet engine event that they sent agents to monitor the family members. The Mystery Woman, seen during Sparkle Motion's talent show performance, was a talent scout from "Star Search" (1983).
When Donnie tells Gretchen he accidentally burned down a house, they are walking directly in front of Jim Cunningham's house. The Life Line Exercise Card that Donnie reads is about a girl finding a lost wallet. Later, Donnie finds Jim Cunningham's wallet on the sidewalk outside his mansion.
Jim Cunningham depicts drugs, alcohol, and premarital sex as "instruments of fear." In the movie, Donnie smokes a cigarette, drinks alcohol, and engages in premarital sex. The climax of the movie occurs after he surrenders to all three temptations.
Jim Cunningham shoots himself on the golf course on October 12th, 10 days after Donnies death. When police searched his house for a suicide note they found all of his furniture and other belongings removed from the empty house. His child porn dungeon was never found.
Roberta Sparrow eventually dies a few months later on 25th December 1988, she was 101 years old.