It's impossible enough to find a decent apartment these days, let alone the humans to share it who won't dismember you in the night. Far more difficult, however, is deciding which roommate pays which portion of the rent, which has been known to end more than one friendship before it even started. A new online tool says it can divide your rent, and it uses math, so you can't possibly argue about it.

Spliddit is the creation of Carnegie Mellon computer scientists who "provide easy access to carefully designed fair division methods, thereby making the world a bit fairer." At the core of this particular tool is an algorithm which assigns rooms and then dictates a price for each room. It essentially works like a mini-real estate market: The divided rents are based on the terms that the roommates themselves set for deciding which rooms are "better" than the others:

We assume that the benefit a participant derives from getting a room she values at x for rent y is x minus y. We use the participants' reported values for rooms to run a market-based algorithm, which iteratively increases the prices of overdemanded rooms and decreases the prices of underdemanded rooms.

Don't live with roommates? There's also tools for dividing up goods (like in a divorce settlement) and a way to divide credit (like in research papers). I'd like to see one for dividing up a dinner bill just to see what Spliddit's quest for fairness dictates, even when someone orders three more margaritas than anyone else then demands to split the tab evenly.


Apparently using math to divide rent is kind of a thing. The New York Times came up with its own formula for how to divide rent back in April, using a mathematical theorem called Sperner's Lemma which is similar to Spliddit's approach but based on triangles and looks super complicated. But you don't need to know the theorem because a rent division calculator reproduces the math for you.

I haven't lived with people I'm not married to in a very long time, but as I remember it, this process traditionally required a very long and heated meeting where at least one person walked away with a room they did not want, and another who felt they'd gotten screwed on price. Anyone who has roommates, have you used one of these things? Would it help you to rest easier—and enjoy your living situation—knowing that an algorithm could decide such financial matters for you, once and for all? [Spliddit]