Uneven does not mean arbitrary
An equal split is popular because it needs no discussion, not because it is fair. In most flats it quietly charges one person for a box room with no window and gives someone else a double with its own bathroom at the same price. Once anybody notices, the equal split stops being the peaceful option and becomes the thing people are annoyed about.
Every uneven method in this article is the same piece of arithmetic wearing different clothes. You give each person a weight — square metres, take-home pay, nights in the flat, anything you can agree on — and then divide the total in proportion to those weights:
person's share = total × (their weight ÷ sum of all weights)
Because the weights are divided by their own sum, the shares always add back up to the total. That is the property to hold on to, and it gives you the only test that matters: add the shares up and check you get the rent. If they do not, the split is wrong, however reasonable each individual number looked.
Two rules make the difference between a method people accept and one they resent. Choose the weights before anyone knows which room they are getting, because a rule agreed in the abstract feels like a rule and a rule agreed afterwards feels like a negotiation you lost. And write the resulting numbers down as monthly figures, not as percentages you re-derive every month.
By room size, in square metres
Area is the most common uneven method because it is measurable, it is nobody's opinion, and a tape measure settles arguments that adjectives cannot. The mistake people make is dividing the whole flat's area, which charges each person for the kitchen and living room in proportion to their bedroom — and there is no reason at all why the person with the big room should get more of the sofa.
Do it in two parts instead:
- Measure each private room. Length times width is close enough; be consistent about whether built-in wardrobes count.
- Measure the shared space — kitchen, living room, hall, shared bathroom — and give every person an equal slice of it, because everyone has equal use of it.
- Add the two together to get each person's chargeable area, then apply the weights formula.
Worked example: three rooms, one en-suite, one parking space
A flat of 96 m² at £1,920 a month. The bedrooms are 18, 13 and 11 m² (42 m² in total), which leaves 54 m² of shared space. Split that 54 three ways and each person carries 18 m² of it.
| Person | Private room | Share of shared space | Chargeable area | Base rent |
|---|---|---|---|---|
| Ama | 18 m² | 18 m² | 36 m² | £720.00 |
| Bo | 13 m² | 18 m² | 31 m² | £620.00 |
| Cal | 11 m² | 18 m² | 29 m² | £580.00 |
| Total | 42 m² | 54 m² | 96 m² | £1,920.00 |
Now the two things a tape measure cannot price. Ama's room has the en-suite. There is one parking space and Bo is the one with the car. Both are exclusive use of something the others cannot use, so both are premiums — and a premium is only fair if the money goes to the people who gave the thing up.
The flat agrees the en-suite is worth £45 a month and the parking space £30. Each premium is paid by the person who gets it and rebated equally to everyone who does not: £45 split between Bo and Cal is £22.50 each; £30 split between Ama and Cal is £15 each.
| Person | Base rent | En-suite | Parking | Pays |
|---|---|---|---|---|
| Ama | £720.00 | +£45.00 | −£15.00 | £750.00 |
| Bo | £620.00 | −£22.50 | +£30.00 | £627.50 |
| Cal | £580.00 | −£22.50 | −£15.00 | £542.50 |
| Total | £1,920.00 | £0.00 | £0.00 | £1,920.00 |
£750.00 + £627.50 + £542.50 = £1,920.00. The premium columns each sum to zero, which is the check that tells you a premium has been rebated rather than invented.
One refinement worth knowing: if the en-suite is a room you can measure, you can skip the guesswork and simply count its floor area inside Ama's private area instead of pricing it. Measure what is measurable; price only what is not.
Pricing the things nobody can measure
Area does not capture the balcony, the north-facing window, the bedroom over the pub, the room you have to walk through to reach the bathroom, or the parking space. These need a number, and the number is a matter of judgement, so the honest goal is not the objectively correct premium — there is none — but a premium everybody can live with.
Three ways to land on one:
- Use the local market
- Look at what rooms in comparable flats near you are advertised at with and without the feature. An en-suite in a shared flat is usually a modest premium rather than a dramatic one; a parking space in a city where parking is scarce can be worth more than a bigger bedroom.
- The swap test
- Ask the person with the feature: at this premium, would you swap rooms with Cal? Then ask Cal: at this premium, would you swap into Ama's? If both say no, the premium is roughly right — each of them prefers the deal they have. If either says yes, move it.
- Sealed bids
- Everyone writes down privately what they would pay for each room, adding to the rent; the allocation that raises the most goes ahead and the surplus above the rent is rebated equally. It is the most robust method and the most effort, and it is set out with a worked example in our guide to splitting rent and bills with housemates.
Whatever you pick, keep the premium as a flat monthly amount rather than folding it into the per-square-metre rate. It stays visible, it is easy to revisit when the person with the car sells the car, and nobody has to reverse-engineer the arithmetic to see what they are paying for.
By income
Splitting by income is a different kind of decision from splitting by area. Area prices what you get; income prices what you can afford. It is common between couples and among friends with very different salaries, and it is unusual between strangers on a joint tenancy — partly because it needs everybody to disclose their pay, which is a real cost of the method and not a detail.
The straightforward version uses take-home pay as the weight. Say the same £1,920 flat, with monthly take-home of £2,800, £2,100 and £1,600 — £6,500 in total:
- £1,920 × 2,800 ÷ 6,500 = £827.0769… → £827.08
- £1,920 × 2,100 ÷ 6,500 = £620.3077… → £620.31
- The third person pays the remainder: £1,920 − £827.08 − £620.31 = £472.61
That last line is deliberate, and the next section explains it: the raw third share is £472.6154, which rounds to £472.62, and if all three round independently the shares come to £1,920.01. Taking the last share as the remainder is what makes the column add up.
Everyone here pays 29.5% of their take-home, which is the appeal: the burden is identical even though the amounts are not.
The harsher variant: income above a floor
Strict proportionality ignores the fact that some costs do not scale with pay. A version that people on lower incomes usually prefer is to give everybody a personal allowance first and split the rent in proportion to what is left. With a £1,000 floor, the weights become £1,800, £1,100 and £600 — £3,500 in total — and the shares are £987.43, £603.43 and £329.14 (again the last one is the remainder). Same rent, same incomes, and the top earner pays about £160 a month more than under strict proportionality.
Neither is more correct. Choose one on purpose, and be aware of what income splitting drags in with it: a pay rise becomes a rent rise, a redundancy becomes everyone else's problem, and somebody has to be told when a bonus lands. Agree in advance how often you will recalculate — once a year is plenty — so that nobody's payslip is a monthly conversation. Between people who are not partners, a simpler compromise is often better: split by area, and let the person with the lowest income take the smallest room.
A mid-month move-in
Rooms rarely change hands on the first of the month. The fix is a daily rate for the room, not for the flat: take that room's monthly share, divide by the number of days in that particular month, and multiply by the days each person actually has it.
Continuing the example, Cal's room is £542.50 a month. Cal leaves and Dee takes the room from 12 June. June has 30 days, so:
- Daily rate: £542.50 ÷ 30 = £18.0833… a day.
- Dee has the room from the 12th to the 30th inclusive — 19 days: 19 × £18.0833… = £343.5833… → £343.58.
- Cal has it for the first 11 days, and pays the remainder: £542.50 − £343.58 = £198.92.
£343.58 + £198.92 = £542.50, so the landlord's rent is covered exactly and neither Ama nor Bo is affected at all. Divide by the days in the actual month rather than by 30 every time, or February and July quietly disagree with each other.
Two things that are not rent and should not be treated as it. The deposit is not an expense — it is money held and, in the normal case, returned, so the incoming person buys it from the outgoing one directly and it never touches the rent arithmetic. And an overlap, where two people have keys for a few days because one is still moving out, is a favour or a negotiation, not a split: decide it explicitly, because pro-rating both of them for the same days charges the room out twice.
A bill that arrives quarterly
Quarterly bills are where mid-month arrivals get messy, because the bill lands after somebody has already left and it covers days they were there for. Splitting it between the people who happen to live there on the day it arrives is simply wrong, and it is the most common way flats end up owing money to someone who has moved out.
Use person-days. Count the days each person was in the flat during the billing period, add them up, and that sum is the divisor.
A water bill of £191.10 covers 1 April to 30 June — 91 days. Ama and Bo were there throughout. Cal was there from 1 April to 11 June, which is 30 + 31 + 11 = 72 days. Dee arrived on 12 June: 19 days.
| Person | Days in the quarter | Share |
|---|---|---|
| Ama | 91 | £63.70 |
| Bo | 91 | £63.70 |
| Cal | 72 | £50.40 |
| Dee | 19 | £13.30 |
| Total | 273 | £191.10 |
£63.70 + £63.70 + £50.40 + £13.30 = £191.10, and Cal owes £50.40 towards a bill that arrived after Cal left. That is the number to have agreed on the way out, not to discover afterwards.
Three refinements, in order of how much they matter:
- Collect a float. If a quarterly bill is predictable, put a twelfth of the annual estimate aside each month per person. Then a departing housemate has already paid, and the true-up when the real bill lands is small.
- Read the meter on move-in and move-out day for anything metered. A photograph of the meter with a date beats any pro-rata formula, because it is what was actually used rather than what an average person would have used.
- Do not pro-rate standing charges by usage. The fixed daily charge on an energy bill is for having the supply at all, so person-days is exactly the right divisor for it even if one housemate was away for three weeks.
Bills in one person's name, deposits, and who owns the shared vacuum cleaner are covered in more detail in splitting rent and bills with housemates.
Somebody has to take the extra penny
Uneven splits produce fractions of a penny almost every time, and no amount of cleverness makes them go away. Money has two decimal places; proportions do not.
The simplest case is the clearest. Three people split £2,000 equally: £666.6666… each. Round each one to £666.67 and the three shares come to £2,000.01 — a penny more than the rent. Round each one down to £666.66 and you are a penny short. There is no split of £2,000 into three equal amounts of whole pennies, so somebody pays £666.67 and somebody pays £666.66, and pretending otherwise just moves the problem.
The rule that always works:
Round every share except one to the nearest penny. Set the last share to total − the sum of the others. The column now adds up exactly, and the person taking the remainder is off by at most a penny or two.
Then two conventions that stop it being a grievance. Rotate who takes the remainder — the person who took it in January does not take it in February. And where the amounts are small enough that the arithmetic is not worth it, round to something human instead: agree that rent is £750, £628 and £542 rather than £750.00, £627.50 and £542.50, as long as the three still add to £1,920. Deliberate rounding that adds up is fine. Accidental rounding that does not is what leaves a flat £3 short every month and nobody knowing why.
One thing not to do: never fix the rounding by adjusting the total. If the shares must add to a fixed rent, the rent is the constraint and the shares bend to it, not the other way round.
Write it down, then revisit it rarely
An uneven split is a small agreement, and it wants to be written somewhere all of you can see, not remembered. Six lines is enough: the total rent, each person's monthly share, the premiums and what they are for, the method (and its weights), the day of the month rent is due and who pays the landlord, and how a mid-month change is pro-rated.
Set a single point in the year to revisit it — at renewal is the obvious one — and otherwise leave it alone. Rooms are also the wrong thing to keep re-litigating: if the balance of the flat has genuinely changed, swapping rooms is often a better answer than re-pricing them.
Two limits worth being plain about. Whatever you agree between yourselves does not change the tenancy: on a joint tenancy the landlord can usually pursue any of you for the whole rent, so an internal split is a promise between housemates and not a defence. And this is a guide to arithmetic, not legal advice — check your own agreement, and your local rules, before relying on any of it.
Where Splitright fits
We make one of the tools this article describes, so read this section accordingly. Splitright is a free app for iPhone, iPad and Android with no accounts, no ads, no subscription and no tracking: one person creates a group, shares a six-character code, and everyone with the code opens the same group from their own phone.
For an uneven flat it does the recurring part rather than the design part. Each expense can be split equally, by exact amounts or by percentage, so the £750 / £627.50 / £542.50 rent above goes in as exact amounts — which is what you want for a fixed rent, because exact amounts always add to the total while percentages have to be rounded. A quarterly bill goes in the same way once you have worked out the person-days, and someone who was not in the flat for that period is simply left out of that expense's participants. It keeps a running balance per person and suggests the smallest set of payments that clears it, which matters in a flat where one person pays the landlord and the others pay that person.
What it does not do: it will not work out the splits in this article for you, there is no recurring or scheduled expense, no CSV or PDF export and no receipt scanning, and it does not move money — it gives you the amounts and you pay however you already do. It is not a backup. And the group code is the credential: anyone holding it can open and edit the group, there is no per-person login, and access cannot be withdrawn from one person, so treat it like a password and share it only with the flat.
If your flat needs export, receipt photos or a long-running ledger tied to accounts, another app is the better answer — our comparison page says which and why. Related: splitting expenses without making anyone sign up, a Splitwise alternative with no account and splitting costs on a group trip.
Common questions
- Is it fair to split rent by room size?
- It is fair as long as you charge for shared space separately. Measure each private room, then give everyone an equal share of the kitchen, living room and hall, because everyone has equal use of those. Dividing the whole flat's area in proportion to bedrooms charges the person with the big room for more of the sofa, which nothing justifies.
- How do you charge for an en-suite or a parking space?
- As a flat monthly premium paid by the person who has exclusive use of it and rebated equally to everyone who does not, so the total rent is unchanged. To sanity-check the amount, ask whether the person paying the premium would swap rooms at that price and whether anyone else would swap in. If both answers are no, the premium is about right.
- How do you work out rent for someone moving in mid-month?
- Divide that room's monthly share by the number of days in that particular month to get a daily rate, and multiply by the days each person actually has the room. Round one person's figure to the nearest penny and set the other's to the room's monthly share minus it, so the two together come to exactly what the landlord is owed.
- Who pays the extra penny when the rent does not divide evenly?
- Someone has to, because proportions have more decimal places than money does. Round every share except one and set the last share to the total minus the sum of the others, then rotate who takes the remainder from month to month. Never adjust the total to make the rounding tidy.