See if this sounds familiar: three roommates are sharing a house or apartment. The rooms range in size from nice and spacious to a glorified closet, yet the rent is divided equally three ways. Been there? Yeah, me too. Not cool. A closet-like room might be just the thing for someone, but they sure don’t want to be paying nice and spacious room rates. So, how do you go about dividing the rent fairly?

Recently, the New York Times created a rent calculator, “designed to produce an ‘envy-free’ division of the rooms.” The calculator is based on a triangle tool, designed by math professor Francis Su using Sperner’s Lemma. Because people have different ideas of what makes a good, fairly-priced room, researchers have found that it works well to have the housemates all weigh in on the rent for each room. Using this method, the calculator takes into account all opinions and turns the room division process from an exercise in guesstimating into a mathematical proposition.

The next time you need to divide the rent fairly, stop guessing and use the calculator.

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