How to split expenses with roommates
Almost every argument between flatmates about money is really an argument about a rule nobody wrote down. The amounts are small and the resentment is not. This guide is the set of rules worth agreeing in the first week, the arithmetic behind the one genuinely contested item, and a way of keeping the record that does not depend on anybody's memory.
Agree these five things before the first payment
- What counts as shared. Rent, utilities, internet and cleaning supplies almost always do. Groceries sometimes. One person's oat milk does not. Write the list on the fridge; the point is that it exists, not that it is perfect.
- Who pays the bill and who reimburses. Utilities usually have to sit in one name. That person is not the group's bank, so they should be paid back on a schedule, not when they get around to asking.
- One settle-up day a month. Pick a date, usually just after everyone is paid. Squaring up on a known day removes the entire category of awkward reminder.
- How rent is divided. The section below is about this. Decide it before anybody moves in, because it is impossible to renegotiate afterwards without somebody feeling ambushed.
- What happens when someone leaves. Notice period, deposit, and who finds the replacement. Nobody wants to discuss it in month one, and everybody wishes they had in month eleven.
Splitting rent when the rooms are not the same
Dividing rent equally is right only when the rooms are equal. They rarely are: one bedroom has the window and the wardrobe, another is barely wider than the bed. The fair version weights each person's share by their private space while keeping the shared space equal, because nobody uses more of the kitchen by having a bigger bedroom.
Here is the method on a real example. A flat costs 450.00 a month with three bedrooms of 18, 14, 12 square metres, and roughly 40% of the floor area is communal.
| Room | Area | Shared 40% | Private 60% | Rent | Split evenly |
|---|---|---|---|---|---|
| Room 1 | 18 m² | 60.00 | 110.45 | 170.45 | 150.00 |
| Room 2 | 14 m² | 60.00 | 85.91 | 145.91 | 150.00 |
| Room 3 | 12 m² | 60.00 | 73.64 | 133.64 | 150.00 |
| Total | 44 m² | 180.00 | 270.00 | 450.00 | 450.00 |
The communal 40% divides three ways evenly. The remaining 60% divides in proportion to bedroom area. The person in the smallest room pays 16.36 a month less than an even split would have charged them, and the person in the largest pays 20.45 more. Run your own numbers through the bill split calculator in weighted mode.
Two adjustments worth knowing. An en-suite or a balcony is private space, so add it to that room's area. A room that nobody wants, the one facing the main road, can take a flat discount agreed by the group; fairness here is a negotiation, and the arithmetic is only there to make the negotiation honest.
Bills, and why the meter reading matters
Utilities divide evenly by default, and that is usually correct: everyone has a fridge and everyone showers. The exception is a bill that one person genuinely drives, an air conditioner running all day in one room while everybody else is at work. If it comes up, the cheap fix is a fixed monthly adjustment agreed in advance rather than an attempt to meter one room.
Always photograph the meter on the day someone moves in or out. A bill that straddles a move is the single most common cause of a flatshare dispute that involves actual money, and a photograph settles it in ten seconds.
Groceries: pick one of these, not both
There are only two schemes that work. A common pot: everybody contributes a fixed amount monthly, all shared food is bought from it, and one person tops it up. It is the least admin and it requires trust about what counts as shared. Everyone buys and logs: whoever is in the shop pays, records it, and it is settled at the end of the month. More entries, less trust required, and it is self-correcting because everyone can see the running list.
What does not work is a hybrid where some things are pooled and some are logged, because the boundary moves and nobody agrees where it was.
Settle in one payment each, not one per person
By the end of a month in a three-person flat there can be six separate debts. There do not need to be six payments. If A owes B and B owes C, A can pay C directly and two debts close with one transfer. In a four-person flat this typically turns six payments into three, and the saving grows with the size of the group. The trip cost splitter on this site does exactly that calculation and will do it for a flat as happily as for a holiday.
Keep the record somewhere everyone can see
A note on one person's phone is not a shared record. Neither is a chat thread, where the receipt you need is always four hundred messages up. What works is a list everyone can add to and everyone can see, so nobody has to be the person who chases.
That is what Splitty is. One group holds one running record: everybody adds what they paid, the balances update for everyone at once, and the settle-up screen reduces the payments needed to square the house. It is free to use, the flatmates you invite can join from a link without creating an account, and it runs in 52 languages, which is often the practical difference in a shared flat where people do not all read the same one. Native apps are available on the App Store and Google Play, and the installable web app works on Android and desktop from the browser.
If you are weighing it against the obvious alternative, there is a dated, factual comparison with Splitwise.