Most of an electricity bill is shared: lights, fridge, the router, the kettle. Then one roommate plugs in something that runs for hours. An air conditioner. A gaming PC. An EV charger. Splitting the whole bill three ways stops feeling fair.
You have three practical options.
Option 1: a flat surcharge
The heavy user pays a fixed extra each month. Everyone else splits the rest.
It's quick and needs no equipment. The downside is that it's a guess. Agree on the amount, and agree to revisit it after a few months or when the season changes. An AC in summer is a different story from an AC in spring.
Option 2: measure it with a plug-in meter
A plug-in energy meter sits between the wall socket and the device and shows the kilowatt-hours (kWh) used. Read it at the end of the billing period, then multiply by your price per kWh.
This is the most accurate option for anything that plugs into a normal socket. It won't work for an AC that is wired in. Many EV chargers show the kWh delivered on their own display or app; if yours does, use that.
Option 3: estimate with wattage x hours
No meter? Estimate it.
kWh = watts / 1000 x hours per day x days
The wattage is usually on the device's label or spec sheet. Hours per day is an honest guess from the person who uses it. Your price per kWh is on the bill: divide the amount by the kWh used.
Worked example (illustrative numbers)
Three roommates, a 30-day month. The electricity bill is $150 for 750 kWh, so the price is $0.20 per kWh. One roommate, Sam, has a gaming PC.
- Sam's PC: 400 W, about 4 hours a day.
- kWh: 400 / 1000 x 4 x 30 = 48 kWh.
- Cost: 48 x $0.20 = $9.60.
Take that out of the bill first: $150 - $9.60 = $140.40. Split it three ways: $46.80 each.
- Sam pays $46.80 + $9.60 = $56.40
- The other two pay $46.80 each
Check: $56.40 + $46.80 + $46.80 = $150.00.
The same method works for an AC. At 1,000 W for 6 hours a day, that's 180 kWh, or $36.00 at the same price. Numbers here are examples, not typical figures. Use your own.
Which option should you pick?
- Small device, low friction: flat surcharge.
- Big, regular load and plug-in access: plug-in meter.
- Wired-in AC or no meter: wattage x hours, reviewed now and then.
Whatever you pick, write it down. A line in your group chat is enough.
Run the numbers
Once you have the heavy user's share, you can enter the rest of the bill in the utility bill splitter for the equal split.
FAQ
Should the AC owner pay all the cooling costs? If only their room is cooled, usually yes. If the AC cools shared space, split it.
What if the PC is only on some weeks? Estimate average hours across the month, or measure with a plug-in meter.
Is a flat fee really fair? It's fair when everyone agrees to it and checks it from time to time.
Keep track of who owes what
Billmates is a web app, still on the waitlist, that tracks who owes what in a shared home. It never holds or moves your money. You pay each other the way you already do. Roommates join from a browser link. No ads. Leave your email if you want to hear when it's ready.