For most of us, the pact is half-hearted - a non-binding agreement to soothe you while you bide your time for the right person.
However, one Reddit user has asked the question we all wanted to know the answer to - do these marriage pacts ever have a happily ever after?
Kevin Spicy asked: "Has anyone married as a result of a "if we are still single by (age)" pact? How did it work out?"
Within 24 hours, over 6,000 commenters shared their experiences, and some of the answers may surprise you.
1throw9away79, said: "Kind of. We left our spouses around the same time (not for each other) and decided to share a house. We were in our mid-thirties by then and sick of the dating scene, so we just laid it out like a business arrangement."
He added: "What started off as an "arrangement" eventually evolved into something extremely serious and passionate. We've been together now for almost seven years and married for almost one. We are extremely in love and I have zero regrets."
He wasn't the only one to prove that romance isn't always the key to the relationship getting off the ground.
BattleStag17 said: "She was the loud, popular, social butterfly, I was the awkward sheltered kid. By way of sheer luck and proxy we became very close friends in high school."
"Like I'm sure many of you have experienced yourself, I couldn't not crush on her something fierce, but I obviously wasn't going to make the move on someone so far out of my league and ruin our friendship.
"I forget exactly how the conversation came to be, but at one point she brings up how we should totally get married if we're both still single by the time we're 30.
"Years later I make a Facebook page (waaay behind the curve like anything else in the social realm), we get back in contact. The conversations get longer. And then she brings the pact back up.
"We're getting married in October, five full years before the pact would've happened."
Although lots of people had success, cagebiter reminded us all of the reality of getting married out of desperation rather than love. "My aunt did. Lasted for a few years until they split."
"And since then she has been married 7 other times."
Erm, maybe not.