Quarterly bills are the most common cause of housemate disputes, because they arrive long after the consumption and rarely match the current occupants.
The fix is simple arithmetic plus one habit at move-out.
The principle: days in the period
The bill covers a period. Each person owes for the days they lived there during that period, not for whether they happen to be present when it arrives.
This sounds obvious and is routinely got wrong, usually because the person who left is no longer in the group chat and it is easier to split it among whoever is still there.
| Person | Days in the quarter | Share of 91 days | Owes of a 273 bill |
|---|---|---|---|
| Ana, whole period | 91 | 35.7% | 97.50 |
| Ben, whole period | 91 | 35.7% | 97.50 |
| Cleo, left 15 Feb | 46 | 18.0% | 49.30 |
| Dev, moved in 15 Feb | 45 | 17.6% | 48.20 |
| 255 person-days | 100% | 292.50 |
Note that the person-days total is what you divide by, not the number of people. Add each person's days, divide the bill by that total to get a per-day rate, then multiply by each person's days.
In the example, 273 divided by 255 person-days is 1.07 per person-day. Slight rounding differences are normal and not worth chasing.
The float that removes the problem
Better than splitting the bill correctly is not having a large bill to split.
Collect a monthly amount from everyone into a household pot sized at roughly a third of the expected quarterly bill. When the bill lands, it is already funded, and everyone has paid in proportion to the months they were there automatically.
This also removes the seasonal shock. A winter energy bill arriving as a single number in February is painful. The same amount collected across three months is unremarkable.
Meter readings at every change
The one habit worth enforcing.
When anyone moves in or out, take a photo of the meter that day. It costs ten seconds and it converts every future argument about a heavy usage period into a fact.
It matters most when usage genuinely changed. If someone worked from home all winter with the heating on and then moved out, a days-based split undercharges them and a meter reading proves it.
Settling with someone who has left
Do not wait for the actual bill. They will be harder to reach every week that passes.
Estimate their share on the day they leave, using the last bill as a guide and the days they were present. Take it then, and agree in writing that you will square up the difference either way when the real bill arrives.
In practice the difference is usually small enough that nobody bothers, which is fine as long as both sides knew that was likely.
Which bills this applies to
Anything billed in arrears for a period rather than monthly in advance.
- Water, often billed every six months
- Energy, where usage is billed after the fact
- Council tax, if paid in instalments over a period
- Broadband where an installation or exit fee spans a change of occupants
- TV licence and similar annual charges
Rent is the exception and works the other way, since it is paid in advance for a defined month. Do not apply the days calculation to rent unless someone moved mid-month.
Record it as it happens
The arithmetic is easy. The hard part is remembering who was there when, six months later.
Log move-in and move-out dates somewhere shared the day they happen, alongside the bills themselves. EconoGlance keeps the group's expense history with dates attached, so working out a days-based split later is a matter of reading rather than remembering. See roommates and splitting rent and bills.
