Settling up the flatshare

A flatshare is not a project with a beginning and an end, it is a standing arrangement: the people change, and not all costs are divided the same way. That is exactly what CostDivider is built for — several groups side by side, each with its own key, and a settlement suggestion for today's position whenever you want one. Setting it up takes half an hour and then holds for years.

In short

1. Several groups rather than one — one per cost type, each with its own division.
2. In every group, set your own share; as the creator you start at 0.
3. Give everybody the right to record expenses.
4. Settle once a month and record the payments as deposits.
5. Start a new group whenever the household changes.

Why several groups

A group has one division. In a flatshare that rarely fits everything:

• Rent and utilities — usually by room size, so unequal.
• Household (cleaning products, loo roll, light bulbs) — usually in equal parts.
• Groceries, where you cook together — in equal parts, but not necessarily with everybody: anyone who never eats along does not belong in it.

Three groups, three divisions. They sit next to each other on the start page, and every expense lands in exactly one of them.

Why this cannot be avoided: who takes part in what is decided by membership of the group, not by the individual expense. There is no expense "for two of the four" — for that there is a group with those two in it.

Choosing the division

In equal parts: give everybody the same percentage. How high does not matter — CostDivider turns equal percentages into equal shares.

By room size: hand out percentages accordingly, say 38 / 32 / 30. Do they have to add up to exactly 100? No: CostDivider balances that out, so the shares always cover the full cost. You can therefore work in square metres just as well — 22 / 18 / 17 does the same job as 38 / 32 / 30.

Fixed amount: somebody paying a negotiated amount regardless of what actually comes up gets a fixed amount. Fixed amounts are taken off first; the percentage members divide the rest.

That is exactly what gives the pattern for the classic case: whoever has the smallest room pays a fixed amount, and the others divide the rest by percentage.

Who may do what

Whoever creates a group administers it. Four rights can be handed on individually:

• Manage expenses
• Manage members
• Edit the group
• Grant rights

In a flatshare, one rule holds in practice: everybody may record expenses. Anything else is a reason for somebody to photograph a receipt in the evening and forward it rather than entering it themselves. The other three rights can stay with whoever created the group.

The monthly rhythm

A flatshare group is not locked — it keeps running. Settling still works, like this:

1. Over the month, everybody records what they laid out.
2. On a fixed date — the first, say — you look at the balances.
3. Whoever is in the red transfers to whoever is in the black.
4. That transfer is recorded as a deposit, with the recipient named.

A deposit from one member to another is a shift, not new money: it credits the payer and debits the recipient by the same amount. After the settlement everybody is back at zero and the next month starts clean — in the same group, without anything having to be deleted.

CostDivider suggests who transfers how much to whom, with as few transfers as possible. In a running group a note above it says the amounts can still change — which for a flatshare is always true, and is precisely why you need a fixed date for this.

When somebody moves in or out

Here is the one thing to know about CostDivider before it hurts:

The settlement knows no periods of time. A member's share is always computed from the group's total — not from the day they joined.

Somebody who moves in in June and joins a group that has been running since January also carries, arithmetically, a part of February's expenses. For a gift that is intended; in a flatshare it is wrong.

Two ways to handle it:

• Clean and recommended: settle before the change, lock the old group, start a new one — "Flatshare household from 06/2026". The old one stays as a record and can be read back.
• Pragmatic: stay in the running group and give the newcomer a fixed amount for the first month that reflects their real share. It works, but it asks for one piece of mental arithmetic — and for everybody to understand why there is an odd number sitting there.

On moving out, the same in reverse: settle while the flatmate is still reachable. A member whose account is deleted later stays in the settlement as an "inactive member" — their balance is real money that everybody else's figures rest on, and so it does not disappear.

Five moves that carry a flatshare settlement

• Separate the cost types. Rent and loo roll have different keys — one group each, and both divisions stay right permanently.
• Set your own share in every new group. The creator starts at 0 everywhere; one glance per group and it fits.
• Hand out the recording right. Whoever shops records it themselves — that is the difference between a settlement that runs and one that hangs on a single person.
• Fix a monthly date. Settling once a month keeps the amounts small and readable. The settlement suggestion is available at any time for that, in a running group too.
• A new group for new flatmates. A share always applies to the group's entire cost — with a fresh group from the move-in date, nobody pays retrospectively.

Worth knowing

• Somebody records the rent monthly. The app does not create recurring expenses by itself — on the other hand it is two minutes a month, and you see immediately whether everybody is keeping up.
• Reminding people is up to you. CostDivider sends no chasers; the outstanding balance sits visibly on the group page instead.
• Shares belong to the membership, not to the individual expense. That keeps a group consistent over months; for a one-off case you create a second group.
• The money moves through your own accounts. CostDivider does the arithmetic and shows the result, the transfer happens in your banking app — it is ticked off here, and the standing is right again for everybody.

Common questions

How many groups make sense?

As many as you have different divisions. Two to four is typical. More gets hard to survey, fewer forces you into a division that does not fit.

Does everybody need an account?

No — a personal link is enough to see your own figures. Anyone who is to record expenses themselves does need an account.

What if somebody does not eat along?

Then they do not belong in the groceries group. That is the clean way, and it is exactly what it is there for.

Can we change the shares later?

Yes. Just note: the change acts on the whole group, not only from today. If that is not what you want, this is the moment for a new group.

Example figures. Green means the group owes that person money; red means they owe the group.

Next

• Settling up utility costs for a house or flat
• Settling up a shared holiday
• Settling up a shared gift
• Settling up a shared move-in budget
• Splitting the running costs when part of your home is used for a business
• Collecting money for one bill, with everybody who joins sharing it