The film is based on the 1972 novel of the same name by Mary Rodgers, in which mother and daughter switch their bodies, and they get a taste of each other's lives. The cause of the switch is left unexplained in this film, but occurs on Friday the 13th, when Ellen and Annabel, in different places, say about each other at the same time, "I wish I could switch places with her for just one day." Rodgers adds a waterskiing subplot to her screenplay.
Ellen Andrews (Barbara Harris) and her daughter, Annabel Andrews (Jodie Foster) constantly quarrel. Following a disagreement on Friday the 13th, Annabel leaves to join a friend at a local diner. In sync, Annabel and Ellen (who is in the family home's kitchen) both wish aloud, "I wish I could switch places with her for just one day". Their wish comes true when they switch their bodies and subsequently lives.
Ellen and Annabel continue to live their everyday lives as each other. Annabel remains at home, tending to laundry, car repair, grocery deliveries, carpet cleaners, dry cleaners, her housemaid, and the family Basset Hound, Max. As though Annabel did not have her hands full, Bill Andrews (John Astin) coerces her to cook dinner for twenty-five as his catered dinner party plans fell through. Annabel enlists Boris, a neighbor whom she has harbored a crush, to look after her younger brother and help make a chocolate mousse but all three manage to mess everything up, then later saving face by making everything into a smorgasbord. Annabel does have a bright spot with her brother, Ben, such as getting to have personal discussions with him, when she picks him up from school. He tells her which qualities he envies about Annabel, and is able to share her loathing over the housemaid, who is constantly complaining about Annabel's sloppiness, and then confesses when he tried to be messy to connect with Annabel, the housemaid said he didn't know better and cleaned up after him. Plus, between all the talks, they play baseball which adds to their affection. These combined situations lead to Annabel's remorse for misjudging Ben and getting a different outlook on him.
Ellen attends school as Annabel where she struggles with marching band, destroys her entire typing class's electric typewriters, exposes her photography class's developing film, and leads the school's field hockey team to a loss. However, Ellen does have one bright point, in a US history class where she accurately recounts the Korean War, having lived through the 1950s as a little girl. In an effort to escape school, Ellen (as Annabel) runs to Bill's office. There, she encounters Bill's new attractive, young, and immodestly dressed secretary. Ellen attempts to intimidate the young woman by sharing how frightening "her mother" is. This effort appeared successful as the secretary adopts more modest clothing, glasses, and an unflattering hairstyle. Ellen (as Annabel) asks Bill for access to his credit card in order to make herself over as her braces were scheduled to be removed that afternoon. Bill approves, and chalks up his secretary's awkward appearance to personal problems at home as her son is ill and her husband is unemployed, causing Ellen to scold herself for not trusting her husband.
The day ends in a comical twist when the mother-daughter pair wishing a new request: to return to themselves. This does happen, although in a different manner than before: they are physically transferred, with Annabel suddenly sitting now behind the wheel of a car with Ben and Boris, with none of them knowing how to drive and attracting the attention of several squad cars. Ellen in turn, finds herself water skiing as she (as Annabel) was scheduled to participate in an aquacade. Bill, who has prospective clients at the aquacade, fears unemployment as he sees Ellen flailing helplessly on skis, but her antics amuse the clients so much that Bill wins the account.
With a new understanding of each other's lives, mother and daughter forgive each other. Following the events of Freaky Friday, Annabel begins dating Boris. Bill is playing cards with Ellen, still trying to understand what happened. Ellen and Bill are fine with Boris taking Annabel to a pizzeria for a date, and Annabel surprises Ben by letting him tag along with them. Ben complains that he never gets to do fun stuff like his dad, who is getting ready for a business trip the following Saturday dirt biking with a Japanese motorcycle firm looking to enter the US market, while Bill says Ben should be more appreciative of a worry-free childhood. Ben remarks he would love to spend one Saturday in his dad's shoes, while Bill says the same about Ben, causing Annabel and Ellen to get nervous and urge Bill and Ben to drop the matter. As they wish to switch their places, Ellen nervously throws her cards into the air while Annabel facepalms.Barbara Harris as Mrs. Ellen Andrews/Annabel Andrews
Jodie Foster as Annabel Andrews/Mrs. Ellen Andrews
John Astin as Mr. Bill Andrews
Patsy Kelly as Mrs. Schmauss, an alcoholic hired by Mrs. Andrews to do minimal house cleaning.
Dick Van Patten as Harold Jennings, Mr. Joffert's Assistant
Vicki Shreck as Virginia, Annabel's Schoolmate
Sorrell Booke as Mr. Dilk, the Principal
Alan Oppenheimer as Mr. Joffert, Mr. Andrews' Boss
Ruth Buzzi as Opposing coach
Kaye Ballard as Coach Betsy
Marc McClure as Boris Harris, a neighbor who is Annabel's crush.
Marie Windsor as Mrs. Murphy, the Typing Teacher
Sparky Marcus as Ben Andrews
Ceil Cabot as Miss McGuirk, the English Teacher
Brooke Mills as Mrs. Lucille Gibbons, Mr. Andrews' Secretary
Karen Smith as Mary Kay Gilbert
Marvin Kaplan as Carpet cleaner
Al Molinaro as Drapery man
Iris Adrian as Bus passenger
Barbara Walden as Mrs. Benson, the History Teacher
Shelly Jutner as Hilary Miller
Charlene Tilton as Bambi, a Schoolmate
Lori Rutherford as Jo-Jo, a Schoolmate
Jack Sheldon as Lloyd, an Auto Detailer
Laurie Main as Mr. Mills, the Darkroom Technician
Don Carter as Delivery boy
Fuddle Bagley as Bus driver
Fritz Feld as Mr. Jackman, the Band Instructor
Dermott Downs as Harvey manager
Jimmy Van Patten as Cashier
Neither Barbara Harris nor Jodie Foster did any actual water skiing in the film. In both cases, these scenes were achieved with the use of professional water skiers in long shot on location, and cutaway shots of the actresses in front of a rear projection effect. Foster did, however, play field hockey in the film.
Barbara Harris and Jodie Foster were nominated for the Golden Globe Award for Best Actress – Motion Picture Musical or Comedy for their roles in this film, with Harris also receiving a nomination in the category for the Alfred Hitchcock film Family Plot. The film also got a nomination for Best Original Song – Motion Picture for the song "I'd Like to Be You for a Day," written by Joel Hirschhorn and Al Kasha.