By room size or by income — see what each person actually pays.
Enter each room's size in square feet. Rent is divided in proportion to those numbers.
Even split, for reference
What each person would pay if nobody's figure differed.
Each share is rounded to the cent and the leftover cents go to the largest shares, so the column adds up to the rent exactly.
Enter each room's size and the rent is divided in proportion to those numbers: a 120 sq ft room in a 600 sq ft flat pays 120 ÷ 600, which is 20% of the rent. The detail that decides whether the answer is fair is which sizes you enter — use the private rooms only. If you add the shared kitchen and hallway into everyone's figure, every room grows by the same amount and the split quietly drifts back towards an even one.
Switch to By income and enter each person's monthly take-home pay; rent is then divided in proportion to income, so someone earning 3,000 of a 5,000 total pays 60%. Use take-home rather than gross — the point of an income split is what each person can actually hand over each month, and two people on the same salary in different tax situations do not have the same money left.
The income mode handles the arithmetic, but there is a decision inside it that no calculator can make: splitting by income means the higher earner pays more every month, including after a raise. A common middle path is to split by income and then check the gap between the two amounts shown above. If that gap feels wrong for the room you both actually share, switch to By room size and compare — the two modes usually land much closer than people expect.
Only if the difference is real, and it is usually smaller in money than in feeling. The parts of the flat you both use most — kitchen, bathroom, living space — are identical for everyone, so a room that is 15% larger does not translate into 15% more of the rent being "yours". Run both rooms through the page and look at the actual gap in dollars; if it comes out at a few dollars a month, the even split is often the one that stops being argued about.
Count them as one person in room-size mode, because they occupy one room, and then let them divide that single share between themselves. If you count a couple as two people you are splitting the rent by headcount rather than by space, and the person alone in the other room ends up subsidising them. In income mode it is the opposite — there you want every earner entered separately, since the split is by money rather than by rooms.
Set the stepper to 3, enter the three room sizes, and read the three amounts off the list. Two things worth checking before you agree to it: whether the rooms are genuinely different enough to justify different rents, and whether the largest room also has the best light or the en-suite — if it does, the size gap understates the difference, and you may want to agree an adjustment on top of what the calculator produces.
They do — that is what the rounding step is for. Each share is worked out to the cent, then the leftover cents are pushed onto the largest shares, so the column sums to the rent exactly. Without that step, three people splitting 1,000 would each show 333.33 and the landlord would be a cent short every month. The same step is why the percentages add to 100.0% rather than 99.9%.
It is fair on ability to pay and unfair on use of space, and which of those matters depends on why you are sharing at all. Income splitting suits couples and close friends who treat the flat as a shared home; room-size splitting suits people who chose a specific room and would happily have taken a smaller one. This page does not choose for you — it shows both numbers, so the argument is about the rule rather than about the arithmetic.