Splitting utilities pro rata means each roommate pays according to the days they were home or the share of the bill their usage caused. An equal split of the electricity bill is simple, but it stops being fair the first time someone is away for two weeks and still gets charged a third.
Skip the spreadsheet: the free pro rata calculator on this site runs the daily-rate math for you.
Which bills deserve a pro rata split
- Electricity and gas. Usage drops when someone is away. Split by days home.
- Water. Same logic, if the bill period lines up with the stay period.
- Internet. Usually a flat monthly fee. Split equally unless someone is away for a full billing cycle.
- Streaming and subscriptions. Split by who uses them, not pro rata. These are opt-in costs, not household costs.
The rule of thumb: pro rata for usage based bills, equal for flat fee bills, opt-in for anything only some people use.
The days method, with numbers
Three roommates share a $240 electricity bill for a 30 day period. Alex was home 30 days, Sam 30 days, Jo 10 days (Jo traveled the rest).
- Total days home: 30 + 30 + 10 = 70
- Rate: $240 ÷ 70 = about $3.43 per day
- Alex pays $102.86, Sam pays $102.86, Jo pays $34.29
Jo's share drops from $80 under an equal split to $34.29, which reflects that a third of the usage did not happen while they were gone. The fridge and standby devices still draw power, so some households charge the away person a small base amount instead of zero. Agree on that before the next trip.
When usage, not days, is the better weight
Days works when absences cause the difference. If one roommate runs a home server or an electric heater, days understate their share. In that case split the bill into a base portion (divided by days) and a usage portion (estimated from the known heavy device). Estimation is fine: the goal is a split nobody argues about, not metering precision.
Split the bill now: enter the bill total and each share. The calculator returns each person's amount instantly, free and no signup.
Seasonal bills and the rounding trap
Winter heating bills can double. A pro rata split still works; only the total changes. Watch the rounding step: $240 ÷ 70 gives a repeating decimal. If everyone rounds their own amount, the three parts may sum to $239.99 or $240.01. Assign the leftover cent to one person in advance. Our guide on how to calculate pro rata works through this trap in detail.
Related guides
How to split rent pro rata How to calculate pro rata: formula and worked examples What does "pro rata" mean?Frequently asked questions
How do you split utilities when one roommate is away for a week?
Use the days method: add up the days each person was home during the billing period, divide the bill by that total, and multiply by each person's days. The traveler pays only for the days they were home.
Do you split internet pro rata?
Usually not. Internet is a flat monthly fee that does not drop when someone is away. Split it equally, or pro rata only when someone is gone for an entire billing cycle and the household agrees to it.
What if one roommate uses much more electricity?
Split the bill into a base portion divided by days and a usage portion assigned to the heavy user, based on the known device (heater, server, mining rig). Estimate rather than meter, and agree on the numbers before the bill arrives.