Finally, Computer Scientists Come Up With A Way To Split Rent That Is Undeniably Fair

You want the room with the biggest window? For less than what I pay? Let’s consult Spliddit.

Finally, Computer Scientists Come Up With A Way To Split Rent That Is Undeniably Fair
[Top photo: Hulton Archive/Getty Images]

Rent can turn otherwise friendly people into selfish monsters. If a renter can jack up the price on a subletter, he will. But as for splitting the monthly rent checks among leasees, how do roommates decide who pays what? It’s possible to have a five-hour discussion at the kitchen table that goes over everyone’s specific wants and needs, but it’s more likely that roommates end up exhausted or dissatisfied. (If this is untrue to your personal experience, consider yourself exceptionally lucky.)


Where that kind of decision-making fails, math becomes glorious. Carnegie Mellon University computer scientist Ariel Procaccia wanted to see if he could build an algorithm that could divide rent in an unequivocally fair way. The result is strikingly, beautifully simple: A website called Spliddit that simply asks the renters how much they’re willing to bid for certain rooms, and spits out a fair price for each.

That’s not all. If someone whines, the algorithm will explain itself. “Each person gets a personal explanation saying why it’s fair, and that’s what’s making this compelling,” Procaccia says.

HTJ via Shutterstock

Spliddit does more than calculate fair division among renters. Procaccia and his team also developed versions for splitting up goods, like inheritances, and assigning credit for academic or business projects. For the latter, a different version of the algorithm asks project team members to assign value to their other team members as if they themselves were not part of the equation. By not trying to rank your own position, the algorithm doles out a fair assessment: “Alice did 60%, Bob did 30%, Charlie did 3%,” Procaccia ventures. “You can then take these exact credit numbers and order authors in an [academic] paper.”

If what Procaccia is suggesting is true, his creation is nothing short of revolutionary. Well, maybe that’s a bit unfair. The mathematical literature on fair division has been around since the 1940s, Procaccia explains, but it’s only rarely been applied to real-life scenarios. The computer scientist simply looked at what was already out there, tweaked it, and made it useful to the general public.

Since the beginning of the month, 30,000 people have visited Spliddit and nearly 5,000 people have divided rent or goods or credit using the app, which runs free-of-cost on some of Amazon’s donated cloud. The feedback’s been positive–people are asking Procaccia if he can do more specific versions of the algorithm, like one that will calculate how a band should split payments for a practice space, or how teachers might use the algorithm to grade group projects.

And yet, even for a website so focused on making sure everyone gets his or her fair share, Procaccia says he won’t be trying to commercialize it in any way. He’s gotten some interested parties, sure, but monetizing research isn’t his thing. “I have this purist view of academia,” Procaccia says. “This is part of my job, making my research relevant to the world.”

About the author

Sydney Brownstone is a Seattle-based former staff writer at Co.Exist. She lives in a Brooklyn apartment with windows that don’t quite open, and covers environment, health, and data.