The Ultimate Roommate Calculator: How a Math Geek Splits the Rent

Living with roommates raises plenty of questions.

Who left the dishes in the sink? Where's your share of the cable bill? What happened to my leftover pizza?

Thankfully, a graduate student at Harvard University has used math to help roommates find an easy answer to the most difficult of domestic questions.

Jonathan Bittner's SplitTheRent.org has an online calculator that can serve as an arbiter of fairness, aiding housemates in divvying up the rent based on room size and amenities.

Harvard graduate student Jonathan Bittner has created a rent calculator that he says will keep you from having a rent-splitting headache.

Courtesy Jonathan Bittner

If sharing an apartment with a roommate is hard, then finding a fair way to split the rent can seem impossible. Thankfully, Harvard graduate student Jonathan Bittner has come up with a formula that he says will keep you from having a rent-splitting headache.

According to Bittner, going 50-50 doesn't mean you're necessarily doing things fairly.

Got lots of windows? That's worth more. No closets? That's a deduction. Your housemate is sharing a room with a significant other? That's where things get complicated.

"I think that everybody really wants to do right by each other," said Bittner, who is studying to become an astrophysicist. "When you are living with friends, you don't really want to have to argue about this -- you can just split it, but that can lead to resentment. Picking a number is also really stressful.

"Most people want to do what's fair, but they need to figure out what fair is," he explained.

That's where SplitTheRent comes along.

Before launching the site, the 26-year-old Harvard Square resident sent surveys to his friends asking them to rank the features that should carry the most weight when it comes to rent.

"The factors that are most important, no surprise, are privacy and space," he explained.

He then created a Web-based calculator that uses algorithms to prorate rent by the square foot, while also taking into account an apartment's perks and faults, from street noise to small closets.

"Not having a door is the most important factor," said Bittner. "One of my places in Boston didn't have a door."

Other important factors include private bathrooms, room size and double occupancy -- meaning a couple sharing one bedroom. Among the least important factors are the distance from the bedroom to the bathroom and living room.

Creating your own math equation that weighs all of these variables isn't easy, so it's no surprise that Bittner's website has found a following online. Over the past few weeks, Bittner said SplitTheRent has racked up more than 100,000 page views.

One of the reasons it has become so popular is because the site's answers tend to closely mirror the rent breakdowns that many roommates come up with on their own. (According to a recent survey, Bittner said his site gives numbers accurate to within 10 percent of what his visitors believe rents should be.)

So if the calculator will just match your intuition, why use the tool in the first place?

Because it's good to have an unbiased mediator, Bittner said.