Ted: Robin Scherbatsky - will you be my backup wife?
Robin: A girl always dreams of hearing those words. Yes, yes, a million times, yes!
Two unlucky-in-love Platonic Life-Partners or Friends with Benefits, not wanting to grow old alone, agree to marry each other if they're still single after a certain age. Can be played either sincerely or for laughs, but either way it's likely to be a Friendship Moment.
Sometimes this trope is seen from the other side; an Old Flame (usually one who's never been mentioned before) shows up to remind a character that they once made such a pact together, and they're here to collect on the deal. Hilarity Ensues, especially if they've aged into an Abhorrent Admirer and the other character doesn't want them any more. If one party has forgotten about it entirely or never took it seriously, the other may say "It Meant Something to Me".
- An interesting variant is used in the My Little Pony: Friendship Is Magic fanfic "Relax". The protagonist and the prostitute he regularly sees make plans to marry assuming that he survives the war and she hasn't been either moved away, fallen for somebody else, or been bought as a personal Sex Slave. It's quite heartwarming.
- Brought up but ultimately averted in Romance and the Fate of Equestria. Twilight, still a Broken Bird from her previous relationship, isn't ready for another and wants herself and Donut Joe to be Friends with Benefits. As the hope of a relationship with her was the only thing keeping him in Equestria, he decides to go through with his plan to take a five-year journey with the travelling Bazaar, leading Twilight to propose this trope if they're both still single when the Bazaar returns to Equestria. Through further discussion, they realize that this trope would be too heartbreaking if only one of them was single, so Twilight instead suggests that they remain faithful to one another and stay in touch for the next five years, and get together at the end no matter what.
- Advice and Trust has a variation in a (possibly non-canon) omake. Asuka and Shinji both make each other promise that one of them is rendered comatose/dead/otherwise incapacitated, that the other would marry Rei instead and name a child after them.
- A boy in the hand by Dogbertcarroll, a lighthearted story featuring a Ranma/Hotaru pairing, reveals in chapter 4 that Minako and Makoto have one of these - if they're both single by the time they're thirty, they'll marry one another. And Minako's willing to shorten the waiting period to thirty days. Makoto's not particularly eager, but has decided that if it means keeping Minako from being alone, she's willing.
- My Best Friend's Wedding subverts this trope. The main character and her best friend have one of these pacts. When he calls her as the deadline birthday is approaching, she thinks hes calling to cash in on the deal—only to discover hes actually calling to tell her hes gotten engaged (to someone else) and to invite her to his wedding.
- A variation in When Harry Met Sally...: Harry and Sally agree that if either of them ever don't have a date on a national holiday, they will take each other to whatever party they're going to as a date. Sally eventually gets sick of this saying that she doesn't want to be Harry's "consolation prize". They get married about three months later when it becomes clear that they actually had feelings for each other.
- In Överenskommelser by Simona Ahrnstedt, Seth has one of these with his New Old Flame Lily Tremaine. They're friends rather than lovers, but still decide to get engaged. But in the end, they break it up when Seth is reunited with Beatrice (the story's female protagonist) and Lily finds true love with Alexandre (with whom Beatrice had a similar relationship).
- Discussed and averted in A Brother's Price: The princesses are all very fond of their cousin, Cullen Moorland, and at least one of them would like have a fallback marriage pact with him. However, her sister points out he is too close a relative. As the the male Gender Rarity Value could lead to inbreeding, they're much stricter about this than most real life societies.
- In Jonathan Tropper's This is Where I Leave You, Judd and Penny made this pact during their college days. Sadly, this didn't carry over in the film adaptation of the book, making Penny (played by Rose Byrne) look more like a Manic Pixie Dream Girl rather than Judd's oldest and best friend, which is weird considering Tropper himself also wrote the screenplay.
- In Happy Endings, Penny is mentioned as having a marriage pact with Butt-Monkey Shershow, who ends up getting married in the first season finale, prompting Penny to fake being engaged to not feel bad about her own singledom.
- Ted and Robin make one in How I Met Your Mother, which pretty much (but not entirely) marks the end of their Will They or Won't They? arc. Apparently the term "Ted & Robin pact" has entered the vernacular. This is discarded as of season 7, when Ted decides he wants to move on from Robin forever and can't do that while the possibility is still there.
Ted: I can't do that anymore. As long as the door's even a little bit open, I have this feeling that I'll just be waiting around to see if I win the lottery when you turn forty.
- When Chandler and Monica get engaged, the other girls start to feel insecure about their own love lives, both still being single at this point. However, Phoebe says she made a pact with Joey years ago that they would marry each other if they were both still single when they were forty. This inspires Rachel to ask Ross to make a similar pact with her. However, Ross claims he already made that deal years ago... also with Phoebe. Both men are indignant when they find out, while Phoebe claims she needs a backup for her backup. By the end of the episode, they all settle on Ross being Rachel's backup, and Joey being Phoebe's. By the end of the series, it doesn't make much of a difference. Ross and Rachel finally decide they want to be together forever in the finale, and while Joey is still single, Phoebe has fallen in love with and married another man. Note that this is well before any of them have turned forty.
- A variant in another episode; Chandler suggests to Monica that if neither of them are married by the time they're forty, they could have a child together. (This was before they were dating). It doesn't go like he expected.
Monica: Why won't I be married when I'm forty?
Chandler: Oh, no, no. No. I just meant hypothetically.
Monica: Okay. Hypothetically, why won't I be married when I'm forty?
Chandler: No! No, no—
Monica: No, what is it? Seriously, is there something fundamentally un-marriable about me?
Chandler: (fumbles at back) Dear God, this - this parachute is a knapsack! (Rolls off of chair)
- Carla Noll in Reunion is Aaron's best friend and hidden secret admirer for years. She's happy to hear him say that if they're still single in a few years that they'll marry each other.
- In one episode of Frasier, it sounds like Roz is about to suggest one of these, and Frasier agrees to marrying her if they are both indeed single at the time. Turns out Roz was going to suggest they kill each other instead.
- In JAG, Harm and Mac agree to have a child together if neither have a significant other some time in the future.
- In The Office, Michael Scott suggests this to Pam (at least in terms of having a baby together) if they're still single in ten years. She shoots it down immediately... and, ever the salesman, he starts haggling. When he suggests that they do so if she's still single in thirty years, she thinks about it for a very long time and agrees.
- A variant in Psych: In "A Very Juliet Episode," a flashback shows that Juliet made an agreement with a college boyfriend to meet up in 7 years, whether they are seeing other people or not, and catch up as well as see if they want to rekindle their relationship. When he doesn't show, Shawn and Gus find him, but things quickly become complicated as it's revealed that he's in the witness protection program. Eventually, they decide to part ways as friends, and meet up in one more year.
- On Seinfeld, Kramer proposes to Elaine that they marry each other if they're both still single in ten years. She makes a counteroffer of fifty years (which he accepts).
- Hudson and Mrs. Bridges — the butler and cook — of Upstairs Downstairs have this arrangement. In one episode Mrs. Bridges seems to have found true love and Hudson offers to release her from their friendly agreement. Unfortunately her beloved turns out to be a jerk.
- Murphy Brown has Murphy and Frank discuss the idea at a point when it seems like their romantic prospects are all but dead, but they let it drop and move on.
- Glee: Towards the end of the series, twenty year old Artie and Tina decide that if they aren't married by the time they're thirty, they'll marry each other since they're best friends. In the "Where Are They Now?" Epilogue though, we see that in five years they end up dating again anyway.
- Peejee proposes this to Davan in Something*Positive as a way to guarantee neither of them grows old alone, which she is especially worried about as even their regular group of friends has largely gone their separate ways. Davan refuses, promising he'd never abandon her anyway and shortly thereafter Davan meets Vanessa, whom he would eventually marry. It was the climax of a long bout of Ship Tease the creator had used to taunt the shippers who wanted Davan and Peejee together, since them not getting romantically involved is one of the few iron-clad rules of the comic, promised to the real woman upon whom Peejee is based.
- Something of a parody in Drawn Together: Captain Hero and Unusually Flexible Girl were Friends with Benefits in college and promised that if they were still single at 30, they'd get married. She shows up to collect. Seems in actuality, she was deliberately holding out for him.
- A variant in American Dad!: Stan asks his dentist to be his "back-up wife" in case he ends up outliving Francine. Hilarity Ensues when Francine finds out and decides to get herself a "back-up husband" for the same eventuality, in the form of Stan's attractive younger colleague. Unfortunately, it turns out both would-be spouses are taking it a lot more seriously than either of the Smiths expected...
- An episode with a flash of the future reveals Steve and Snot made this pact with each other for if they were single by the age of 30. They both regret picking such a young age.
- Somewhat parodied in Star vs. the Forces of Evil. Rasticore says this to Miss Heinous right before being killed by her.
- In the Italian cartoon Il Figlio dei Venti, Zefiro's love interest Sarah has a mix of this and Childhood Marriage Promise with her friend Etienne. They realized their parents want them together as kids, and agreed to enter a Marriage of Convenience if they came of age and hadn't found love. Oswald intentionally gives Zefiro the wrong idea about the "engagement", and Zefiro believes for three episodes that he's lost Sarah forever before Etienne himself sets the story straight.
- BoJack Horseman: When Todd breaks up with Yolanda, he notes how difficult it would be for them to find other asexual people to date, so he makes a pact to give the relationship another try if they're still single when they turn 100 years old.