How to split rent when the bedrooms aren’t equal

The short version

Split the shared space equally and the bedrooms by size. Everyone uses the kitchen, the shower and the sofa the same amount, so nobody should get a discount on them for having a small bedroom. Work out how much of the apartment is bedroom, divide only that part by room size, and split what is left evenly.

In a 1,050 sq ft apartment at $2,400 a month, with bedrooms of 180, 130 and 110 square feet, that comes out at $891.43, $777.14 and $731.43. Then adjust the weights for the things a tape measure cannot see, which is the part everyone argues about and the part this article spends the most time on.

Why an even split breaks down here

An even split is the right default for most shared costs. Electricity, the internet, the cleaning supplies: everyone gets the same thing, so everyone pays the same amount, and inventing a formula for it would cost more goodwill than it saves.

Rent is different because you are not all buying the same thing. One person gets a room they can fit a desk in and one person gets a room where the bed touches three walls. That difference is not a preference, it is the product, and it shows up every single day of the lease. It is also the most common reason a house share that got on fine for six months suddenly does not.

Start with square footage, because it is the only measurable part

Measure each bedroom. Length times width, in feet or meters, it does not matter which as long as you use the same unit for all of them, because only the ratio between the rooms affects the answer. Pace it out if you have no tape measure. A pace is close enough to a meter that the ratios survive.

Now here is the version almost every rent calculator gives you, and the reason this article exists. Take the whole rent, weight it by bedroom size, done:

• The 180 sq ft room is 42.86 percent of the bedroom space, so it pays 42.86 percent of $2,400: $1,028.57
• The 130 sq ft room pays 30.95 percent: $742.86
• The 110 sq ft room pays 26.19 percent: $628.57

It adds up, it looks rigorous, and it is wrong. The gap between the biggest and smallest room is $400 a month, on rooms that differ by 70 square feet in an apartment where nearly two thirds of the floor space belongs to nobody in particular. Something in that arithmetic is being charged to the wrong person.

The fix: nobody owns the kitchen

The apartment is 1,050 square feet. The bedrooms account for 420 of that. The other 630, which is 60 percent of the place, is hallway, kitchen, living room and bathroom, and all three people use it identically. When you weight the whole rent by bedroom size, you are charging that 60 percent out in proportion to bedroom size too, which is a claim nobody would defend out loud: the person with the big room does not get more kitchen.

So do it in two parts.

One: carve out the shared space

630 of 1,050 square feet is 60 percent of the apartment, so 60 percent of the rent, which is $1,440, is the shared pot. Divide it by three: $480 each, before anyone has mentioned a bedroom.

Two: divide the bedroom money by room size

That leaves $960 attached to the bedrooms, and this is where square footage earns its keep. The same percentages as before, applied to the money they actually describe: $411.43, $297.14 and $251.43.

Add the two halves together and the month looks like this.

The third row is the one to use. It puts the big room $91 above an even share instead of $228, which is the difference between a number the person in the small room can argue for and a number the person in the big room will quietly resent for a year. It is also simply the more accurate answer: it charges each room for the space it actually has exclusive use of, and charges the rest to everybody.

What a tape measure cannot see

Two rooms of exactly 130 square feet are not worth the same money, and everyone knows it the moment they walk in. The list of things that move a room’s value and have no formula attached is long, and these are the ones that actually change what people are willing to pay:

• A private bathroom. The largest single factor, and the one worth the biggest adjustment. It is also a partial refund to everyone else, because one fewer person is queueing in the morning.
• Storage. A walk-in closet is square footage that shows up on the plan. A room with no closet at all is a room that loses floor space to a wardrobe, so its usable size is smaller than its measured size.
• Windows and light. A north-facing basement room and a corner room with two windows are not the same product at any square footage.
• Noise and traffic. The room next to the front door, the bathroom wall, or the kitchen gets woken up by everyone else’s schedule.
• Shape. 130 square feet in a long corridor takes a bed and nothing else. The same area square takes a bed and a desk.

There is no exchange rate for any of this, and anyone who gives you one has made it up. What works is agreeing a percentage on the room’s weight, out loud, before anyone has moved in. A 15 percent bump on the ensuite room and 10 percent off the room with no closet turns the recommended split into $935.78, $766.24 and $697.98.

Run your own numbers

Your rooms are not 180, 130 and 110, so here is the arithmetic above with your figures in it. Put in the rent, the size of the whole apartment, and each bedroom. The adjustment column is the percentage you agreed for the ensuite, the missing closet or the room over the takeout place.

Nothing here is sent anywhere. It runs in your browser, using the same allocator the app uses to divide a real bill, which is why the columns always add back to the rent exactly rather than landing a cent out.

The cases that break the formula

A couple sharing one bedroom

Count people for the shared space and rooms for the bedroom space. Two people in one bedroom use the kitchen and the bathroom as two people, so they pay two equal shares of the shared pot, then split one room-size share of the bedroom money between them. Treating them as one unit throughout is the most common way this goes wrong: it has two people paying one person’s share of the sofa.

Someone moves in mid-lease

Recalculate from the day they arrive rather than backdating anything, and prorate the first month by days. If their arrival changes what the shared space is worth, which it does if the apartment goes from two people to three, that is a new agreement and not an amendment to the old one. Say so explicitly, because the person whose rent goes up will otherwise feel it was decided for them.

Very different incomes

This is a separate question from room size, and mixing the two produces a number nobody can check. Settle the room-size split first, so everyone agrees what each room is worth. If you then want to weight the whole thing by what people earn, do that as a second, visible step. How to split bills when one of you earns more, and it is a much bigger effect than any bedroom.

The lease says something different

Whatever you agree between yourselves, the lease is what the landlord enforces, and on a joint tenancy every name on it is liable for the whole rent rather than for their share. Your split is an agreement about who reimburses whom, not a change to that liability. Worth knowing before somebody stops paying.

Write it down, then stop discussing it

The arithmetic is not the hard part of this. The hard part is that the conversation happens while everyone is choosing a bedroom, which is exactly when nobody wants to be the person haggling. What prevents the argument six months later is that the numbers were agreed once and recorded somewhere neither person can quietly re-remember.

Three lines is enough:

• What each room measures, and what the whole apartment measures.
• What adjustment each room got, and the reason in about five words.
• What each person therefore pays, and when it gets revisited, if it does.

Then let the rent be the boring, settled thing it should be, and go back to arguing about the washing up.

Rent is only the first of the shared costs, and it is the one with the clearest right answer. For the bills, the shopping and everything else that arrives monthly, how to split shared costs fairly covers which method suits which cost, and the fewest payments that settle everyone up turns a month of them into a couple of transfers.

Common questions

Every figure in this article was produced by running Halvy’s own split engine on the worked example, not by rounding percentages, which is why the totals land on the cent. Tenancy law differs by country and by state, and nothing here is legal advice: check what your lease says about joint liability before you rely on any private arrangement.