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Pick the rule before the room. The rent is one fixed number, and the three rules below divide it three different ways: by area, by room, and by income. On a 2,400.00 flat the rule alone moves one person by up to 200.00 a month. Enter the rent, each room's size and each occupant's income to see all three answers side by side.
What the rule alone moves, on rent of $2,400.00
Room 1 pays $972.97 by area · $800.00 by room · $1,000.00 by income. The same $200.00 a month is $2,400.00 over a year.
One row per room. Room size feeds the by-area rule and income feeds the by-income rule; the by-room rule ignores both and gives every room the same share. Room sizes should be the private rooms only.
Every rule divides the same rent, and each rule is rounded on its own, so its shares add back up to the rent exactly.
Three views of the same rent: the three rules side by side, the division behind the by-area figures, and what the choice is worth to one person over a year.
The rent does not change when the rule changes. The same flat, the same 2,400.00, and the same room can cost 972.97 under one rule, 800.00 under the next and 1,000.00 under the third. Nothing about the flat moved — only the question of what the rent is being charged for. That is why splitting rent is decided by the rule and not by the arithmetic, and why the arithmetic is worth doing before the rule is agreed rather than after.
Each rule charges for something different. By area charges for the space a person occupies. By room charges for occupancy: a room is a room, whatever is in it. By income charges for what a person can carry. All three are defensible, and each is unfair in one direction, so the useful question is not which rule is fair but which unfairness the people in the flat can live with for twelve months.
That is also why the order matters. Name the rule before anyone picks a room. Chosen first, the rule belongs to the flat and the rooms are then priced by it. Chosen afterwards, every person will argue for the rule that flatters their own room and their own pay, and a decision about arithmetic turns into a negotiation between friends.
By area turns each room's square footage into a weight, so the biggest room pays most. By room gives every room one identical share, so the only thing being divided is the rent. By income turns each occupant's pay into a weight, so the highest earner pays most. Two of the three need a figure entered per person; the third needs nothing but the rent and the number of rooms.
The area rule goes wrong at the shared space. Kitchens, bathrooms and hallways are used by everyone, so if they are folded into each room's figure, every room grows by the same amount and the split drifts back towards an even one — the rule stops charging for space and starts charging for nothing. Count the private rooms only.
The room rule goes wrong when the rooms are not actually alike. An en-suite, a window, a walk-in cupboard or simply a room that fits a desk are worth real money, and an identical share makes the smaller room pay for them.
The income rule goes wrong at the next pay rise. It is the only one of the three that re-prices itself whenever somebody's circumstances change, and it re-prices upwards for the person who just earned more. That is not an argument against it — it is the reason to write down that the rule follows take-home pay, and to agree what happens when one person's pay moves.
The total. Every rule divides the same rent and every rule's shares add back up to it exactly, to the cent. No rule makes the flat cheaper or more expensive; the rule decides who carries which part, and the tables above are the whole of that decision written out. Every figure is worked out in the browser and nothing is uploaded — the privacy page says what that means, and the about page says who builds these pages.
Same flat, same rent, same three rooms — 2,400.00 of rent, private rooms of 150, 120 and 100 square feet, and take-home pay of 3,500, 2,800 and 2,100. Every cell below is the rent multiplied by that room's weight over the total weight, printed at full precision underneath so it can be checked against the figure above it.
| Rule | The sum behind Room 1 | Room 1 | Room 2 | Room 3 | Rent |
|---|---|---|---|---|---|
| By area | 2,400.00 × 150 ÷ 370 = 41.666667% | 972.97exact 972.972973 | 778.38exact 778.378378 | 648.65exact 648.648649 | 2,400.00 |
| By income | 3,500 ÷ 8,400 = 41.666667% of the rent | 1,000.00exact 1,000.000000 | 800.00exact 800.000000 | 600.00600.000000 | 2,400.00 |
| By room | 2,400.00 ÷ 3 rooms = 800.00 each | 800.00exact 800.000000 | 800.00exact 800.000000 | 800.00exact 800.000000 | 2,400.00 |
| Spread, highest minus lowest | what the rule alone moves | 324.32 by area · 400.00 by income · 0.00 by room | — | ||
The area row does not balance before rounding, and it is not close. Round all three shares down to the cent and you get 972.97 + 778.37 + 648.64 = 2,399.98, which is two cents short of the 2,400.00 rent. The two leftover cents go to the two largest fractional parts measured in cents: 97,297.297 cents has a fraction of 0.297, 77,837.837 has 0.837, and 64,864.864 has 0.864. The 0.864 and the 0.837 are the two biggest, so Room 3 and Room 2 each take a cent and the row reads 972.97, 778.38 and 648.65 — which is the exact total. The income row and the room row need no such step, because both divide into whole cents.
Round every share down to the cent first, then hand the leftover cents to the shares with the largest fractional parts. The parts always add back up to the rent exactly, and the room that gets an extra cent is decided by arithmetic rather than by taste. Ties happen when the fractional parts are identical, as they would be on three equal rooms; the tie is broken by order, so the first-listed room takes the cent.
Enter each private room's size in square feet. Each share is the rent multiplied by that room's area over the total area, so a 150 sq ft room in 370 sq ft of private space carries 150 ÷ 370 of a 2,400.00 rent, which is 972.97. The figure that decides whether the answer is fair is which areas you enter: private rooms only, never the shared kitchen or hallway.
Divide the rent by the number of rooms and give every room the same share. Three rooms and 2,400.00 means 800.00 each. It is the simplest of the three rules, the easiest to remember, and the only one that ignores both the size of the rooms and what the occupants earn — which is exactly why it suits rooms that really are interchangeable.
Enter each occupant's monthly take-home pay and give each person the rent in proportion to it: 3,500 of 8,400 total pay is 1,000.00 of a 2,400.00 rent. Use take-home rather than gross salary, because the point of the rule 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 amount left.
No single answer holds for every flat, and this page does not pick one for you. The area rule suits people who chose a particular room and would have been content in a smaller one; the income rule suits people who treat the flat as a shared home; the room rule suits rooms that are genuinely alike. What this page does is run all three on the same rent, so the argument can be about the rule instead of about arithmetic nobody has done yet.
No. The kitchen, the bathroom and the hallway are used by everyone, so adding them to each room's figure adds the same amount to every room and pulls the split back towards an even one. Count the private rooms only. If the flat wants the shared space to count for something, that is an adjustment agreed on top of the area split rather than a number to hide inside it.
Under the area rule the couple occupies one room, carries one room's share and then divides that share between themselves — counting them as two rooms would be splitting by headcount, not by space. Under the income rule the same couple normally brings two incomes and therefore carries a larger share, because that rule is about money rather than about space. Both are consistent. What is not consistent is counting a couple as one for the rent and two for the utilities.
Because a share of a cent is not a cent. 2,400.00 multiplied by 150 over 370 is 972.9729…, and the same is true of the other two rooms. Each share is rounded down to the cent and the leftover cents are given to the shares with the largest fractional parts, which is why the three area figures end in .97, .38 and .65 and still add up to exactly 2,400.00 rather than a cent or two short.
No. The rent is one number and all three rules divide the same amount, so each rule's shares add back up to it exactly. What the rule changes is who pays which part, and by how much — up to 200.00 a month for the person it moves most in the example on this page, which is 2,400.00 over a year. The flat costs the same either way; the rule decides who carries it.
The split rent calculator takes one rule at a time: you switch between room size and income and read the answer for the rule you selected. This page runs the same rent through all three rules at once, which is what you want while the rule itself is still undecided. Once the rule is agreed, the monthly household bill page adds the utilities to the same figure.