Housemates usually split the rent equally and then someone quietly resents the box room for a year. This lays out four different ways to divide it — equally, by floor area, by area adjusted with premiums and discounts you set yourselves, and by shares you state outright — and shows all four side by side with the per-person monthly figure under each, plus the difference from an equal split, which is the number people actually care about. The adjustment working is printed line by line, because a black-box answer is useless in a negotiation: whoever is being asked to pay more has to be able to check it. Every method's amounts are computed in whole cents and add to exactly the total rent, with one documented remainder rule for the leftover cents, so a split is never a penny off. Shared bills can be split by the same method or a different one. Not one adjustment percentage is built into this tool — what an en-suite is worth is a matter for the people paying it — and it never calls a method fair, correct or recommended. It shows what each method produces; you choose.
Worked example
FAIR RENT SPLIT
3 room(s) · total rent $1,800.00 per month · shared bills $240.00 per month
This tool does not decide anything. It shows what four methods produce, side by
side, so the housemates can look at the same numbers and choose. No method here is
called fair, correct or recommended — each one says what it measures and stops. The
name of the tool is only the phrase people search for.
ROOMS READ
1. Alex — floor area 18 — en-suite +12%, balcony +4% — custom weight 40
2. Sam — floor area 14 — top floor -5% — custom weight 33
3. Jo — floor area 9 — smallest -8%, noise -4% — custom weight 27
RENT PER PERSON, PER MONTH — ALL FOUR METHODS SIDE BY SIDE
Person / room Equal split By floor area Area + adjustments Custom weights
Alex $600.00 $790.24 $892.73 $720.00
Sam $600.00 $614.64 $568.65 $594.00
Jo $600.00 $395.12 $338.62 $486.00
TOTAL $1,800.00 $1,800.00 $1,800.00 $1,800.00
Every column above adds to exactly $1,800.00. That is checked by construction, not by
rounding the display: the last cent is placed by the remainder rule below.
WHAT EACH COLUMN MEASURES
Equal split — nothing about the rooms. Every person pays the same amount, and the
difference from it is what the other columns are arguing about.
By floor area — floor area, in proportion, and nothing else. It cannot see light,
noise, stairs, a bathroom or who has the boiler cupboard.
Area + adjustments — floor area, then the premiums and discounts YOU entered. It
measures your opinion of those features as much as it measures the rooms.
Custom weights — the shares you stated outright. It measures a decision that has
already been made — the arithmetic here only makes it add up.
DIFFERENCE FROM AN EQUAL SPLIT (rent only)
Person / room Equal split By floor area Area + adjustments Custom weights
Alex $0.00 +$190.24 +$292.73 +$120.00
Sam $0.00 +$14.64 -$31.35 -$6.00
Jo $0.00 -$204.88 -$261.38 -$114.00
Column adds to $0.00 $0.00 $0.00 $0.00
Each column adds to zero because every method splits the same total: a dollar more
for one room is a dollar less spread across the others. This row is the arithmetic
check, not a verdict.
SHARED BILLS AND THE TOTAL PER PERSON — bills split by Equal split
Person / room Bills Total · Equal split Total · By floor area Total · Area + adjustments Total · Custom weights
Alex $80.00 $680.00 $870.24 $972.73 $800.00
Sam $80.00 $680.00 $694.64 $648.65 $674.00
Jo $80.00 $680.00 $475.12 $418.62 $566.00
TOTAL $240.00 $2,040.00 $2,040.00 $2,040.00 $2,040.00
The bills pot of $240.00 is split by its own method and adds to exactly that
amount on its own, before it is added to the rent.
WORKING — BY FLOOR AREA
Total floor area across all rooms: 41
Alex: 18 ÷ 41 = 43.90% of $1,800.00 = $790.24
Sam: 14 ÷ 41 = 34.15% of $1,800.00 = $614.64
Jo: 9 ÷ 41 = 21.95% of $1,800.00 = $395.12
WORKING — AREA PLUS WEIGHTED ADJUSTMENTS
Adjustments are ADDED, not compounded: +12% and +4% make +16%, not +16.48%.
The combined figure is held between 1% and 10,000% so no room can reach a zero
or negative share. A premium raises that room's weight BEFORE everything is
renormalised, so a +10% premium does not mean that room pays 10% more than it
would on area alone — it means its weight is 10% higher than the others, and
the money it picks up is money the other rooms put down.
Alex
floor area 18
en-suite +12%
balcony +4%
combined factor 116.00%
weight = 18 × 116.00% = 20.88
share = 49.60% of the total weight
rent = $892.73
Sam
floor area 14
top floor -5%
combined factor 95.00%
weight = 14 × 95.00% = 13.30
share = 31.59% of the total weight
rent = $568.65
Jo
floor area 9
smallest -8%
noise -4%
combined factor 88.00%
weight = 9 × 88.00% = 7.92
share = 18.81% of the total weight
rent = $338.62
WORKING — CUSTOM WEIGHTS
Alex: weight 40 = 40.00% of $1,800.00 = $720.00
Sam: weight 33 = 33.00% of $1,800.00 = $594.00
Jo: weight 27 = 27.00% of $1,800.00 = $486.00
Percentages here are rounded to two decimals for reading. The money is worked
out from the whole numbers you typed, not from the rounded percentage, which is
why multiplying the percentage by the rent yourself can land a cent away.
HOW THE LAST CENTS WERE PLACED
A proportional share almost never divides into whole cents. Each room first gets
the whole cents its exact share covers; that always leaves fewer cents over than
there are rooms. Those go, one each, to the rooms whose share was cut back the most
by that rounding — largest remainder first, ties settled by the order you pasted
them. The rule is the same for every method and for the bills, so the same paste
always produces the same answer.
Equal split — divided evenly, no leftover cent.
By floor area — 1 leftover cent, one each to: Sam
Area + adjustments — 1 leftover cent, one each to: Sam
Custom weights — divided evenly, no leftover cent.
INPUT FORMAT — one room per line:
label | floor area | name=+% | name=-% | w=custom weight
· The label is the person or the room — whatever you all call it.
· The floor area can be in any unit (sq m, sq ft, paces) as long as every
room uses the same one. Only the ratios matter, so the unit is never named.
· Any number of adjustments, each `name=+12` or `name=-8`. The name is free
text: en-suite, north-facing, next to the boiler, no window, top floor.
A `%` sign is optional. Adjustments only affect the third method.
· `w=40` sets that room's share for the custom-weights method. The weights are
normalised, so 40/33/27, 4/3.3/2.7 and 400/330/270 all mean the same thing.
· Separate the fields with a pipe, semicolon or tab. A comma works too, but
only on a line that has none of those, so labels can contain commas.
· Blank lines and lines starting with # or // are ignored.
WHAT THIS TOOL DOES NOT KNOW
· It knows nothing about your local rental market. It has no idea what an en-suite,
a balcony or a north-facing box room is actually worth where you live, which is
why not one percentage is built in — every one of them is a number you chose.
· It has not read your tenancy agreement. If the tenancy is joint and several, every
tenant is liable for the WHOLE rent regardless of what you agree between you, and
no arithmetic on this page changes that.
· It does not know who was there first, who found the flat, who is on the tenancy,
who pays the deposit, who has a partner staying four nights a week, or who is
moving out in March.
· It does not know how the rooms are actually used — a large room that doubles as the
only place to work is not the same as a large room used for sleeping.
· Floor area is not a valuation. Two rooms of the same size can be worth very
different amounts, and that is exactly the gap the adjustments are there to let
you argue about explicitly rather than silently.
· Nothing here is legal or financial advice, and no method is endorsed.
· A short written agreement between housemates — who pays what, from when, what
happens when someone leaves, and how you revisit it — matters more than the
arithmetic. Print the table, agree on a method, write down the one you chose and
the date, and have everyone sign it.
Frequently asked
What do I type in?
One room per line: a label, the floor area, then any number of adjustments and an optional custom weight — for example `Alex | 18 | en-suite=+12 | balcony=+4 | w=40`. The label is the person or the room. The area can be in any unit as long as every room uses the same one, because only the ratios matter. Each adjustment is free text and a percentage, like `north-facing=-6` or `next to the boiler=-4`. Fields are separated by a pipe, semicolon or tab; a comma works on a line with none of those, so labels can contain commas.
Which method should we use?
That is not a question this tool answers, and it deliberately does not have a recommended option. Equal split measures nothing about the rooms. Floor area measures floor area and nothing else — not light, noise, stairs or bathrooms. Area plus adjustments measures the area and then your own opinion of the features. Custom weights measure a decision you have already made. Look at all four columns together and pick the one you can all defend to each other.
Where do the adjustment percentages come from?
From you, entirely. There is no built-in figure for what an en-suite, a balcony or a top-floor room is worth, and there never will be, because it varies by city, by building and by the people involved. If you have no idea where to start, look at what a room with and without that feature is advertised for near you, or start from what each of you would actually pay and negotiate towards the middle.
How are the adjustments combined?
They are added, not compounded: +12% and +4% make +16%, not +16.48%. Adding is easier to check by eye and easier to argue about, which is the whole point of showing the working. The combined figure is held between 1% and 10,000% so no room can end up with a zero or negative share. Every step is printed under 'Working — area plus weighted adjustments'.
If I put a +10% premium on a room, does that room pay 10% more?
No, and the tool says so in the output. The premium raises that room's weight by 10% before all the weights are renormalised, so what it actually pays depends on how big the other rooms are and what adjustments they carry. The money it picks up is money the other rooms put down — the difference-from-equal table shows exactly how much moved and in which direction.
Do the amounts really add up to the rent?
Exactly, every time, for every method. All the arithmetic is in whole cents, never in floating point. A proportional share almost never divides into whole cents, so each room first receives the whole cents its exact share covers, which always leaves fewer cents over than there are rooms; those go one each to the rooms whose share was cut back most by that rounding, ties settled by the order you pasted them. The same paste always produces the same answer, and the output names which room received each leftover cent.
Can we split the bills differently from the rent?
Yes. Bills can be split equally, by floor area, by area plus adjustments, by your custom weights, or by whatever method each column is using. The output states which one was applied. Splitting rent by area and bills equally is a common arrangement, on the reasoning that a bigger room does not use proportionally more hot water — but that is your call, not the tool's.
What about the person who found the flat, or who is on the tenancy?
The tool knows nothing about it. It cannot see who was there first, who paid the deposit, who is named on the agreement, who has a partner staying most of the week, or who is leaving in March. Those things are usually more important than the square footage and they belong in the conversation, not in the arithmetic.
Does this override our tenancy agreement?
No. If your tenancy is joint and several, every tenant is liable to the landlord for the whole rent no matter what you agree between yourselves. A split like this is an agreement among housemates about who contributes what; it does not change anything the landlord can enforce. This is not legal advice.
What should we do once we have picked a method?
Write it down. A short note saying which method you used, the figures it produced, the date it starts, what happens when someone moves out, and when you will revisit it, signed by everyone, prevents far more arguments than the arithmetic does. Print the side-by-side table and attach it, so a year later everyone can see what was agreed and why.