How to split bills with roommates

The most common source of a long-running, unspoken grievance. The person in the box room paying the same as the person with the double and the en suite will notice, every month, for as long as they live there.

How to set the ratio

There is no formula, and pretending there is one causes its own arguments. What works is agreeing the ratio explicitly, using whichever basis everyone finds reasonable:

• Floor area of each bedroom, as a share of total bedroom area. Objective, and easy to measure.
• What each room would rent for individually. Closest to the market, and captures things area misses — light, noise, an en suite.
• A negotiated number everyone agrees to. Perfectly valid, as long as it is stated rather than assumed.

Set as a percentage split, this ratio keeps applying automatically when the rent changes. That is the practical advantage over agreeing three fixed amounts.

The case that breaks naive systems, because for one month the normal split is simply wrong.

1. Work out the departing person's share pro rata by days: their normal share × days present ÷ days in the month.
2. Split the remainder between the people who were there for the whole month, using the usual ratio.
3. Record it as an exact-amount split for that month only.
4. Write the reason in the description — 'Aug rent, Sam left 12th' — so the odd figures still make sense in a year.
5. Return to the normal split next month.

Agree in advance who carries the cost of an empty room. It is a much easier conversation before anybody has given notice.

Keep it out of the monthly ledger entirely. A deposit is not an expense — it is money held by somebody else that will come back, in whole or in part, at the end of the tenancy. Recording it as a shared expense makes every monthly balance wrong.

What to do instead:

• Write down who paid what into the deposit when the tenancy starts, and keep that note somewhere durable.
• If one person paid the whole deposit and others are buying in, record those buy-in transfers as a one-off settlement between the individuals involved, not as a household expense.
• When a housemate leaves and is replaced, the incoming person usually repays the outgoing one directly. That is a transfer between two people, and belongs in a one-to-one ledger.
• At the end of the tenancy, split whatever comes back in the same proportions it went in, minus any agreed deductions.

Someone moving out is the moment every unresolved balance surfaces at once. Work through this before the keys go back:

1. Record every outstanding expense, including anything paid but not yet entered.
2. Calculate the leaver's pro-rata rent and bills for their final month.
3. Check for bills that will arrive after they leave — energy and water are usually billed in arrears, so a final bill often lands weeks later. Agree who pays it and how the leaver settles their share.
4. Settle the ledger balance in full.
5. Deal with the deposit separately, per the section above.
6. Export the ledger to CSV and keep it. If the deposit is disputed months later, a dated record of who paid what is the only useful evidence anyone has.
7. Remove them from the group only after all of this is done.

The third item is the one people forget. A final energy bill arriving six weeks after someone has moved out, with no agreement about it, is the single most common roommate money dispute.

A Home group holds the household. Rent goes in as a percentage split, bills as equal splits, and a pro-rata month as an exact split with the reason in the description. Balances show who is behind without anyone having to raise it, and the roommate expenses page works through a complete month.