When one roommate uses noticeably more electricity, gas or water, split the bill equally and add a fixed top-up from the heavy user to cover the difference. Work out the top-up by estimating the extra use: watts multiplied by hours, divided by 1,000, multiplied by your price per kWh. Use this only for clear, consistent differences, such as a space heater, home working all winter or charging an electric car.
When an equal split is still right
Most of the time, splitting utilities equally is the right answer.
Small differences, one person's longer showers or another's games console, tend to even out and are not worth measuring. The cost of tracking them, in time and in goodwill, is higher than the money involved. Keep the equal split unless the difference is large, regular and obvious to everyone.
| Situation | Change the split? |
|---|---|
| One person takes longer showers | No |
| One person games in the evenings | No |
| One person works from home all day with heating on | Usually yes, in winter |
| One person runs a space heater or air conditioner in their room | Yes |
| One person charges an electric car at home | Yes |
| One person is away half the month, every month | Often yes, by days present |
Method 1: Base plus top-up
Split the whole bill equally, then the heavy user adds a fixed monthly amount for their extra use.
Example: a space heater. A 1,500 watt heater running 6 hours a day for 30 days uses 1,500 × 6 × 30 ÷ 1,000 = 270 kWh. The average US residential electricity price was 18.31 cents per kWh in July 2026, according to the US Energy Information Administration. At that price, the heater costs about $49 a month.
| Without top-up | With top-up | |
|---|---|---|
| Electricity bill | $180 | $180 |
| Heater's share | Split three ways | $49 paid by the heater's owner |
| Remaining bill | $131 split three ways, $43.67 each | |
| Heater owner pays | $60 | $92.67 |
| Each other roommate pays | $60 | $43.67 |
Use your own price per kWh from your bill, which can be very different from the US average. The method works the same in any currency.
Method 2: Measure it
For a single appliance, a plug-in energy meter or smart plug measures its use directly.
Plug the heater, air conditioner or computer into the meter for a month and read the kWh. Multiply by your price. It removes all guesswork, and the number usually ends the discussion. For electric cars, most chargers and many car apps report the energy used for each session.
The formula for anything you cannot measure is the one the US Department of Energy uses: wattage multiplied by hours of use gives watt-hours, divided by 1,000 gives kWh. The wattage is usually printed on the appliance's label.
Method 3: Working from home
Home working raises heating, cooling and electricity for the whole flat, not just one room.
Two fair approaches. Either estimate the extra heating or cooling hours and price them, or agree a simple seasonal top-up, for example the home worker pays an extra 25% share of the heating bill from November to March. If the home worker's employer pays a home-working allowance, that is a reasonable source for it.
Method 4: Split by days present
When one person is regularly away, for example working away half of each month, split variable bills by days present.
Count each person's nights at home in the billing period, add them up and split the variable part of the bill in proportion. Keep fixed charges, such as standing charges and internet, equal, because they do not change when someone is away.
Which bills to adjust
Not every utility is worth the effort.
| Bill | Adjust for heavy use? | How |
|---|---|---|
| Electricity | Yes, for clear differences | Top-up or measured |
| Heating (gas or electric) | Yes, for home working | Seasonal top-up |
| Water | Rarely | Equal, unless the difference is extreme |
| Internet | No | Equal. Anyone wanting a faster plan pays the difference |
| Standing or fixed charges | No | Equal |
How to raise it
This conversation goes badly when it starts with a bill and goes well when it starts with a rule.
- Raise it before the season, not after the bill: 'Shall we agree how heating works this winter?'
- Bring the numbers, worked out with the formula above, so it is about kWh and not character.
- Propose a fixed top-up rather than monthly recalculation.
- Review it at the end of the season.
Write the rule into your roommate agreement. For bills that arrive quarterly and span someone moving out, see how to split quarterly bills when people move out.
Doing it in EconoGlance
Each utility bill can be split differently, expense by expense.
Add the electricity bill, choose exact amounts, and enter the heater owner's top-up on their line with the remainder split equally. Or split by shares, giving the home worker 1.25 shares to everyone else's 1 for winter heating. Recurring bills repeat with the same split until you change it.
For the full roommate money guide, read how to split rent and bills with roommates.
