Rent is the easy part of living with people. It is one number, it arrives on the same day every month, and everyone agreed to it before they moved in.
What ends flatshares is the other thing: the €12 of washing-up liquid, the €80 electricity bill that arrived in one person's name, the internet nobody has settled since March, the shared olive oil that one person cooks with daily and another has never touched. Individually trivial. Repeated four hundred times over a year, and stacked on top of the fact that nobody is quite sure who is up and who is down, they become the thing people actually move out over.
This is a system for handling all of it with about five minutes of attention a month.
Part one: dividing the rent
Equal shares
Total rent divided by number of tenants. The default, and correct whenever the rooms are genuinely comparable.
It stops being correct the moment they are not, and "comparable" is doing more work than people admit. A room 40% larger with a bay window and an en suite is not the same product as the box room over the boiler, and pretending otherwise for twelve months is a slow-acting poison.
By room size
Divide rent in proportion to each bedroom's floor area. Measure once — a phone will do it — and the split is defensible for the length of the tenancy.
The refinement that makes this actually fair: split the rent into two pots first. Shared space (kitchen, living room, hallway, bathroom if shared) is divided equally, because everyone uses it equally. Private space is divided by bedroom area. A 60/40 weighting between shared and private is a reasonable starting point.
Worked example. €2,000 rent, three tenants, bedrooms of 18m², 14m² and 10m² (42m² total).
Shared portion, 40% = €800, split three ways = €266.67 each.
Private portion, 60% = €1,200, split by area = €514.29 / €400.00 / €285.71.
Totals: €781 / €667 / €552.
Compare that to €667 each and you can see exactly what an equal split was costing the person in the small room: €115 a month, €1,380 a year.
By room size, adjusted
Floor area is a proxy, not the whole story. Adjust for the things that obviously differ:
En suite bathroom — a real premium, typically 10–15%.
Natural light and aspect — a north-facing basement room is not the same as a bright top-floor one of identical size.
Noise — the room over the road, or next to the boiler, or with the shared wall to the living room.
Storage — built-in wardrobes versus nowhere to put anything.
Balcony or garden access from one room only.
Run this conversation once, before anyone signs. Every adjustment is easy to discuss when rooms are still being allocated and nearly impossible to reopen in month seven.
Couples
A couple sharing one room occupies less space per person and uses more of the shared amenities. Neither "one share" nor "two full shares" is right.
The common conventions are 1.5 shares, or the room-size method with a modest uplift for the second occupant on the shared portion — since two people do use the kitchen and hot water more than one. Pick one, write it down, move on. This is not a question with a correct answer, only with an agreed one.
Practicalities worth settling on day one
Who holds the tenancy and who pays the landlord. Usually one person pays the full amount and the others pay them. That person is carrying everyone's credit risk, and should say so out loud rather than discovering it in month four.
When internal payments are due. Set it two or three days before the landlord's date, not the same day. The person fronting the rent should not be finding out at 11pm that they are €700 short.
What happens when someone leaves mid-tenancy. The single most expensive thing to leave unagreed. Who finds the replacement, who covers the gap month, what happens to the deposit share. Ten minutes now, or a very bad conversation later.
Part two: utilities
Utilities are worse than rent because they arrive irregularly, in different people's names, in varying amounts.
The single organising rule
Every bill has one named owner who pays it, and it is recorded the day it is paid.
Not at the end of the month. Not when someone gets round to it. The day it is paid, by the person who paid it, split there and then. A bill recorded four weeks later is a bill somebody has to reconstruct, and reconstruction is where the arguments live.
Spread the ownership around — one person on electricity, one on internet, one on water — so no single flatmate is permanently carrying the household's cash flow.
What to split evenly, and what not to
Split evenly: internet, water, council tax or equivalent, TV licence, building charges, cleaning supplies, the shared basics.
Consider splitting unevenly: heating and electricity, when usage is genuinely lopsided. Someone working from home five days a week uses meaningfully more heat and power than someone in an office. A 60/40 adjustment is often closer to the truth than an even split.
Do not split at all: individual streaming subscriptions, personal phone bills, one person's gym. If it does not serve the household, it is not a household cost — even if it feels petty to say so.
Meters, estimates and the annual reconciliation
If your energy bills are estimated and settle up annually, be careful. A household can under-pay all year and then receive a €600 correction — which lands on whoever is living there in month twelve, including people who moved in in month nine and were not there for the usage.
Record the estimate payments as they happen, and when the reconciliation arrives, split it across the period it covers rather than the people who happen to be present. This is only possible if you kept dated records, which is the argument for keeping them.
Part three: the shared basket
This is where flatshare accounting actually breaks. Rent is one transaction a month. Groceries are forty.
Define the shared list explicitly
Write down what the household buys collectively. Typically: cleaning products, toilet paper, dish soap, bin bags, salt, oil, basic condiments, coffee or tea if everyone drinks it.
Everything else is personal, and that includes the expensive version of a shared item. If the household buys own-brand olive oil and one person wants the good stuff, the good stuff is theirs.
The list matters more than its contents. An explicit boring list beats an implicit generous one, because the implicit one is different in every flatmate's head.
Do not itemize the supermarket run
The instinct is to split a €94 shop by item — €31 shared, €63 across three people's personal shopping. It is accurate and it is unsustainable; nobody does it more than twice.
Two systems that survive contact with reality:
The shared-basket-only method. Household items get bought on a separate transaction, split evenly. Personal shopping is personal, paid by the person. One extra trip through the self-checkout, zero accounting.
The rotation method. Whoever shops buys everything, records the total, splits evenly, and the rotation averages it out. Works well when everyone eats broadly similarly. Fails badly when one flatmate is vegan, one eats meat daily, and one exists on takeaway.
Pick based on how similar your consumption actually is, not on how similar it feels.
Meals cooked for the household
A flatmate who cooks for four is contributing labour and ingredients. The ingredients are recordable; the labour is not, and trying to price it is a fast route to a bad flatshare.
The convention that works: ingredients for a shared meal are a shared expense, and cooking rotates. If it does not rotate, that is a conversation about chores, not about money.
Part four: the monthly rhythm
Five minutes, once a month. Same day every month.
1. Everything is already recorded. If step one is "collect receipts", the system has already failed. Each expense should have been recorded when it happened, in fifteen seconds, by whoever paid.
2. Look at the balances. In HiBill, a balance is always between two people — there is no household pot to reconcile, and no arguing about what the group account means. You open a flatmate and see the full two-person ledger: every expense, every payment, what it comes to right now.
3. Simplify the loops. Three flatmates generate circular debts constantly — you owe Sam for the internet, Sam owes Alex for electricity, Alex owes you for the shop. Simplifying collapses these into the fewest payments that leave everyone in the same place, and records a visible entry so nothing moves silently.
4. Settle. Settling is just a transfer that brings a balance to zero, and it can be partial. It sits in the same timeline as everything else, so "did I pay you for the electricity?" has an answer.
5. Note anything odd. The unusually large bill, the thing someone disputes. Deal with it in the five minutes, not in month nine.
Part five: the difficult flatmate
The one who never pays on time
Usually disorganisation rather than bad faith, and the two need very different responses.
Make the amount and the deadline unambiguous and visible — most late payment is genuinely "I did not know what I owed". Then send exactly one reminder. HiBill limits these to one per person per day on purpose: a nudge that can be weaponised stops working the first time someone weaponises it.
If it is chronic, change the structure rather than escalating the nagging. Move them to paying the landlord directly for their share, so their lateness is between them and the landlord instead of between them and you.
The one who disputes a charge
Have the receipt. This is the entire answer.
Attach the photo to the transaction and discuss it in the comments on the transaction itself, so the conversation sits next to the number rather than scrolling away in a group chat. Most disputes evaporate on contact with the actual receipt, and the ones that do not are real disagreements worth having properly.
The one who thinks the split is unfair
Listen, because they are sometimes right — particularly if the flat adopted an equal rent split with unequal rooms.
Renegotiate forward, not backward. Adjusting future months is a solvable problem. Retroactively rebalancing nine months of rent is not, and attempting it will cost more than the money involved.
The one who moves out owing money
Settle before the keys go back, while there is still leverage and goodwill. After someone has moved, an outstanding balance is a favour you are asking, not an obligation you can enforce.
Keep the record accurate either way. An honest ledger with an unpaid balance is a far better position than a deleted record and a grudge.
Frequently asked questions
Should rent be split equally or by room size? Equally when rooms are genuinely comparable; by room size when they are not. The split-the-rent-in-two method — shared space equally, private space by area — handles both and is easy to explain to someone who feels they are being overcharged.
How much more should a couple pay? 1.5 shares is the most common convention. The room-size method with a small uplift for the second person's use of shared amenities is more defensible but harder to agree. Either works; deciding after they move in does not.
What is the fairest way to split utilities? Evenly for the fixed ones — internet, water, standing charges. Consider adjusting the usage-driven ones, mainly heating and electricity, when someone is home substantially more than the others. Adjust by a broad percentage rather than trying to meter individual rooms.
How do you handle a flatmate who is away for a month? Rent and fixed utilities continue — they are still holding the room and the tenancy. Usage-driven costs and the shared basket reasonably pause. Agree the rule before anyone travels, not while they are away.
Do we need a joint account? Usually not, and it introduces problems of its own: it needs everyone's cooperation to open, it is awkward to close, and it obscures who actually contributed what. A per-person ledger with a monthly settle-up gives you the same coordination with none of the entanglement. It is why HiBill has no group pot at all — the reasoning is in why we rebuilt HiBill around people instead of groups.
What if one flatmate is not on any app? Add them as a placeholder and record their share anyway. If they sign up later, merging preserves every transaction and the balance.
The short version
Split rent by what people actually get, and settle it before anyone signs. Give every recurring bill one named owner. Define the shared basket explicitly and keep it boring. Record everything the day it happens. Settle monthly, on a fixed date, after simplifying the loops.
None of this is about distrust. It is the opposite: a household where the numbers are visible and current is a household where nobody has to keep a private tally in their head — and the private tally is what actually corrodes a flatshare.