How to split utility bills when usage isn’t equal

The short version

Weight the bill by how much of the period each person was actually in the apartment, then split in proportion to those weights. Count a day at home all day as one, a day spent out at work as a fraction of one, and a night slept elsewhere as zero.

Then apply the weight only to the bills that move with occupancy. Electricity, gas and heating do. The broadband does not, because it costs the same whether the apartment is full or empty.

Why an even split fails on this particular bill

Most household costs do not care who is home. The rent is the rent, the broadband is the broadband, and the person on a two-week holiday is not saving the apartment any money. Utilities are the exception: heating an occupied living room for eight hours costs real money that an empty apartment does not spend.

So this is the one bill where an even split is not a rounding convenience, it is a transfer. The people who are out all day are buying daytime heat and light they are not in the building for, and because the amount is small every month, nobody raises it until it has been happening for a year.

The framing matters, because the conversation usually goes wrong in the same way: it sounds like a penalty for working from home. It is not. Nobody is being charged for the choice. They are being charged for the electricity, which is what everyone else thought they were splitting.

The worked example

A three-person apartment, one month, a $210 electricity bill. Ada works from home five days a week. Ben is at an office. Cara is at an office too, and away ten nights of the month visiting family.

Count a day where somebody is home in the daytime as a full day. Count a day where they leave in the morning and come back in the evening as 0.6 of a day, because they are still there for the evening, which is when the lights and the cooking happen. That 0.6 is a number the household agrees, not a number anybody measures: see below.

• Ada: 30 days, home in the day, weight 30.0
• Ben: 30 days, out in the day, weight 30 × 0.6 = 18.0
• Cara: 20 days present, out in the day, weight 20 × 0.6 = 12.0

The interesting row is Ben’s. He is home every night and out every day, which is the most common pattern in any shared apartment, and the weighting moves him by seven dollars. That is the honest answer to “is this worth the trouble”: for the typical roommate it is a rounding error, and for the two people at the ends of the range it is not.

Scale it up and the case gets clearer. On a $340 winter bill the same weights give $170.00, $102.00 and $68.00. Over a year on one bill, Cara’s share of the difference is $336, which is not a rounding error in anybody’s budget.

Which bills to weight, and which to leave alone

Weight these

Electricity, gas, heating oil, and water where it is metered. These scale with how many people are in the building and for how long, which is exactly what the weight describes.

Split these evenly

Broadband, the standing charge on an energy bill, any council or municipal charge, contents insurance, and a streaming subscription the house shares. All of them cost the same regardless of occupancy, so weighting them just adds arithmetic to a number that was already right.

And the ones that are neither

Groceries, cleaning supplies and the things people actually use at different rates are a different problem with a different answer, and trying to solve them with an occupancy weight will produce something nobody accepts. How to split shared costs fairly walks through choosing between per-person, per-usage, per-room and per-income before you commit to one.

Split your own bill

Put in the bill, how many days it covers, and who was where. The daytime factor is yours to set: 0.6 is a reasonable starting point for out-at-work, and the point of exposing it is that this is a number your household agrees rather than one the calculator knows.

Agreeing the weights without a spreadsheet fight

These are negotiated numbers, not measurements

No apartment meters a bedroom. There is no reading that proves the person working from home used 50% of the electricity, and any method claiming otherwise is dressing an estimate up as a fact. What the weight does is make the estimate explicit and reviewable, instead of leaving the default estimate, which is that everybody used exactly the same amount, unexamined because it is round.

Agree it for the next bill, never the last one

Set the rule before the money is at stake. Renegotiating after a bill lands turns arithmetic into an argument about that specific bill, and whoever is worse off under the new rule has an obvious reason to reject it.

Round the days generously

Count nights slept elsewhere, not hours out of the apartment. Somebody who was away for “about a week” is seven days. The precision people reach for here is fake, and chasing it is how a two-minute agreement becomes a diary audit that nobody wants to be part of.

Write down one sentence

“Electricity and gas by occupancy-days, out-at-work counts as 0.6, everything else evenly.” That is the whole policy. If somebody moves in or somebody changes job, you revisit the sentence rather than reopening every bill you have already paid.

If the rooms in your apartment are also very different sizes, the same argument applies to the rent, with a weight you can actually measure: how to split rent when the bedrooms aren’t equal.

Common questions

Every figure here was produced by running Halvy’s own split engine on the worked example, which is why both money columns reconcile to $210.00 exactly. The 0.6 daytime factor is an example of a household agreement rather than a measured quantity: no domestic meter can attribute consumption to a person, which is why the calculator above lets you set it.