Utility Bill Split Calculator
Divide a shared utility bill among people by proportional weight, square footage, or any other share you choose.
Equal share (per person)
$90
Weighted share (per row)
What is a proportional bill split?
A proportional split divides a shared bill by assigned weights rather than equally among everyone. The classic equal split – total divided by headcount – works when each person’s share of the underlying cost is the same. A proportional split handles the common case where it is not: roommates with different-sized bedrooms, tenants who share a commercial space in different ratios, or housemates who agreed on an unequal arrangement.
The weight can be any positive number: 1 for equal shares, room square footage for area-based splits, or days of occupancy for time-based splits. The calculator normalizes the weights so only their ratios matter, not their absolute size.
Equal-share amount is shown alongside the weighted breakdown so you can see both approaches at once.
How to calculate a weighted bill split
Formula
each person's share = total bill x (person's weight / sum of all weights)
How the formula works
Each person’s share = total bill x (person’s weight / sum of all weights). The sum of all weights is the denominator; each person’s weight over that sum gives their fraction of the bill. Multiplying by the total bill gives their dollar amount, rounded to the nearest cent.
The equal share is simply the total divided by the number of people, also rounded to the nearest cent.
Choosing weights
Any consistent unit works as long as everyone uses the same basis:
- Square footage of each person’s private space (bedrooms + proportional common area)
- Days occupied in the billing period
- A ratio agreed in writing (for example, 2:1 where one person takes the primary bedroom)
- 1 for each person to produce an equal split
Rounding
Per-person shares are rounded to the nearest cent. With three or more people, the rounded shares may sum to one cent more or less than the total. A common approach is to assign the extra cent to the person with the largest share. Agree on this before finalizing the split.
Checking the result
The sum of all weighted shares should equal the total bill within one cent. If your sum is off by more, check that you entered the correct total and that the weights reflect the agreed arrangement.
How to choose a fair way to split utilities
- Equal: each person pays the same. Works when rooms and habits are similar.
- By room size: use each person's bedroom area plus a share of common space. Fairer when rooms differ a lot and heating or cooling is a large part of the bill.
- By days at home: use the number of days each person lived there in the billing period. Fairer when someone was away for much of the period.
- By an agreed ratio: use any numbers everyone agreed to, for example when one person runs an air conditioner or a second refrigerator.
The best method is the one everyone agrees to in advance and uses every month.
Fixed bills and usage bills can use different methods
Internet and other flat bills cost the same no matter who is home, so many households split them equally.
Electricity, gas, and water change with use, so a split by days at home or by room size can be fairer for those bills. Run the calculator once for each bill and add the results, as Example 3 shows. To estimate a month's bill before you split it, use the Utility Bill Estimator.
Splitting by days at home
Each person's weight is the number of days they lived in the home during the billing period, and the calculator turns those days into shares.
A long-term guest or partner can be counted as an extra person if the household agrees.
When a roommate moves in or out during the billing period
Use the number of days each person lived there during the period as their weight, which gives the same result as prorating. For one person's share of a partial period, the Utility Bill Prorate Calculator gives the same answer.
Settle the last bill before the person leaves, and take their name off the account if they were the account holder.
Put the split in writing
A short roommate agreement helps avoid disputes. Name the account holder, the method for each bill, the date each person pays the account holder, and who covers late fees.
The agreement is between roommates and does not change what each person owes the landlord under the lease.
Example 1: two roommates by days at home
- 1Sum of weights30 + 15 = 45
- 2Person 1 share$180 x (30 / 45) = $120.00
- 3Person 2 share$180 x (15 / 45) = $60.00
- 4Check: shares sum to total$120.00 + $60.00 = $180.00
Example 2: three roommates by days at home
- 1Sum of weights30 + 30 + 18 = 78
- 2Roommate A share$214.50 x (30 / 78) = $82.50
- 3Roommate B share$214.50 x (30 / 78) = $82.50
- 4Roommate C share$214.50 x (18 / 78) = $49.50
- 5Check: shares sum to total$82.50 + $82.50 + $49.50 = $214.50 (an equal split would be $71.50 each)
Example 3: mixed method (equal plus by room size)
- 1Internet, split equally$60 / 3 = $20.00 each
- 2Electricity, sum of weights200 + 150 + 100 = 450
- 3Person 1 electricity$150 x (200 / 450) = $66.67
- 4Person 2 electricity$150 x (150 / 450) = $50.00
- 5Person 3 electricity$150 x (100 / 450) = $33.33
- 6Per-person totals$86.67, $70.00, $53.33 (check: $210.00)
FAQ
What is the fairest way to split utilities with roommates?
There is no single fair method. An equal split works when rooms and habits are similar. If rooms differ in size, or one person is often away, a split by room size or by days at home usually feels fairer. Agree on the method before the first bill arrives.
Should internet be split the same way as electricity?
Many households split internet and other flat bills equally, because the cost does not change with use, and split electricity, gas, and water by days at home or room size. You can run the calculator once for each bill.
How do I split a bill when a roommate moved out partway through the month?
Use the number of days each person lived there during the billing period as the weight. For one person's share of a partial period, the Prorate calculator gives the same result.
Does a roommate who was away still pay for utilities?
That depends on what the household agreed. Some households keep fixed bills equal and reduce only usage bills for time away. Decide this in writing so it does not become a dispute later.
Whose name should the utility account be in?
The account holder is responsible to the utility for the full bill, even if others owe them a share. If the account holder moves out, they should ask the utility to close or transfer the account, and the remaining roommates should open a new one.
Do the weighted shares add up to exactly the total bill?
They should within rounding. Each per-person share is rounded to the nearest cent. With many people, rounding can produce a sum that differs by one cent from the total. Assign the extra cent to one person before paying -- one simple approach is to give it to the person with the largest share.
Sources
1. RentSmart Roommate Agreement (Handout 9)
University of Wisconsin-Madison Division of Extension
Name the account holder; choose an even or stated split; a roommate agreement does not change joint liability under the lease.
https://fyi.extension.wisc.edu/rentsmart/files/2019/10/E-act-5-handout-9.pdf2. Roommates
The Ohio State University, Off-Campus and Commuter Student Engagement
Decide in advance whether an absent roommate still pays a share of utilities.
https://offcampus.osu.edu/resources/housing-resources/roommates3. Electricity use in homes
U.S. Energy Information Administration
Air conditioning and space heating are the largest home end uses, which supports room-size weighting for those bills.
https://www.eia.gov/energyexplained/use-of-energy/electricity-use-in-homes.php4. Changing Utility Service When Moving
Missouri Public Service Commission
The account holder stays responsible to the utility until service is taken out of their name.
https://psc.mo.gov/CMSInternetData/ConsumerInformation/Changing%20Utility%20Service%20When%20Moving.pdf