The premise for this show (a family led by a single working mom) was inspired by actress/writer/single mom Whitney Blake. One of Blake's children, Meredith Baxter, would go on to play a sitcom mom on Family Ties (1982).
According to the book "Archie and Edith, Mike and Gloria: The tumultuous history of All In The Family", the episode All in the Family: Edith's 50th Birthday: Part 1 (1977), where Edith was held prisoner in her home and tormented by a would-be rapist, was originally intended to be an episode of One Day At A Time, with Ann Romano as the victim.
The set used as the travel agency Barbara and Max worked in during the final season was later used as Al Bundy's shoe store on 'Married With Children (1988)'. In a couple of episodes of ODAAT, you can even see the "New Market Mall" sign outside the windows of the travel agency.
Lyrics for the show's theme song: This is it; this is it. / This is life, the one you get, / so go and have a ball! / This is it; this is it, / straight ahead, and rest assured, / you can't be sure at all. / So, while you're here, enjoy the view; / keep on doing what you do. / Hold on tight; we'll muddle through, / one day at a time, one day at a time! / So, up on your feet; up on your feet; / somewhere there's music playing. / Don't you worry none, / just take it like it comes, / one day at a time, one day at a time, / one day at a time, one day at a time, / one day at a time, one day at a time, / one day at a time!
This show was taped in front of a live audience. When they were done filming an episode, Carroll O'Connor and Jean Stapleton would come on stage and sing the theme song from All in the Family (1971) at the piano before presenting an All in the Family (1971) episode to record the audience's responses for that episode's laugh track. (See also 'All in the Family' trivia.)
In the middle of the 1979-1980 season, Julie married Max and moved to Houston. The reason, for this writing is because in reality, Phillips was fired from the show after failing, a drug test and went to rehab.
When Mackenzie Phillips left the show the second time around, her character Julie was written out by first going away for training for her job and then having her leave Max and their daughter Annie. Phillips left the series due to documented substance abuse problems.