How to split rent fairly when rooms aren’t equal

Equal rent for unequal rooms means the person in the smallest room quietly pays for the biggest one. Most households know that, but the alternative feels like haggling. The way out is to agree on a method first and let the numbers follow. This guide explains the room-weighted method housr uses, how to pick the weights, and when it is better to let everyone bid for rooms instead.

1. Step 1Agree the shared-space share
2. Step 2Measure every room the same way
3. Step 3Agree the bath multiplier
4. Step 4Add small factors only if they differ
5. Step 5Run the split and check it
6. Step 6Ask: would anyone swap?

01The method in one sentence

Split the part of the rent that pays for shared space evenly per person, and split the rest by each bedroom’s weight, where weight is floor area adjusted for a private bath and any other differences you agree on. In symbols: pay = shared × your heads ÷ all heads + private × your room’s weight ÷ all weights.

02Step 1: how much of the rent is shared space?

There is no official figure. A practical way to choose is to look at the floor plan: if the living room, kitchen and shared bathroom take up roughly 40% of the flat, use 40%. A flat with a large living room justifies a higher share; a flat that is mostly bedrooms off a corridor justifies a lower one. The higher the shared share, the closer the result is to an equal split.

03Step 2: measure the rooms the same way

Measure wall to wall, and decide once whether closets count. If one room has awkward, unusable space (a sloped ceiling, a corridor that people walk through), use the usable area instead. What matters is consistency: everyone should be able to repeat the measurement and get the same number.

04Step 3: what is a private bathroom worth?

Treat it as a multiplier on the room’s floor area. 1.25× is a reasonable starting point for a full en-suite; 1.1× for a small half-bath; more if the other rooms share one bathroom between three people. The useful check is to ask each person, before anyone picks a room: would you be happy to take either room at these prices? If the answer is yes all round, the multiplier is about right.

05Step 4: small factors, only when they really differ

Closet space, daylight and noise matter to people, but each one should move the price only a little, for example 5% per level. Use them only for rooms that genuinely differ (a room with no outside window, a room above the street), and remember that several small factors add up. Things with a market price, such as a parking space or furniture that comes with one room, are better handled as a fixed monthly amount charged to that room, with the rest of the rent split normally.

06When to bid for rooms instead

Weights work when people broadly agree on what makes a room better. When preferences differ (one person wants the dark room for sleeping during the day, another would pay a lot for the room with the balcony), bidding works better. Each person splits the total rent across the rooms according to what each room is worth to them. Rooms then go to the people who value them most, and the prices are set so that nobody would rather have someone else’s room at its price.

This is the method behind Spliddit’s rent calculator, built on research by Gal, Mash, Procaccia and Zick, whose user study found that people rate the “maximin” envy-free solution, the one that makes the worst-off person as well off as possible, as fairer than other envy-free solutions. housr’s bid mode is its own implementation of the same idea and runs in your browser.

07Check the result together

• Does everyone understand why their number is what it is? Every amount should come with a reason.
• Would anyone swap rooms at these prices? If yes, adjust the weights or switch to bids.
• Do the amounts add up to the rent to the cent? Rounding should never leave someone covering the difference.
• Is the formula written down, so it gives next year’s split when the rent changes?

Sources

1. Assign Rooms and Share Rent, Spliddit. www.spliddit.org/apps/rent
2. Gal, Mash, Procaccia and Zick, “Which Is the Fairest (Rent Division) of Them All?”, J. ACM 64(6), 2017. procaccia.info/wp-content/uploads/2020/03/rent.pdf
3. Francis Su, Fair Division Calculator (Harvey Mudd College). math.hmc.edu/su/fairdivision/