Roommate expense calculator: monthly cost per person

When to use the roommate expense calculator

Use it when the bedrooms differ but the household bills are shared. It applies two rules in one pass: rent follows a weight for each person, and every other shared cost is split equally. The answer is one monthly total per person, which is the number each roommate needs to move into a budget. If the rooms are the same size and quality, an equal split of everything is quicker and needs no calculator.

How does the calculator work?

1. Count the people. Every rent weight above 0 is a person. A weight of 0 means the slot is empty.
2. Split the rent by weight. Each person pays the rent times their weight divided by all the weights added together. The weight can be bedroom square feet or points you agreed on, as long as everyone uses the same unit.
3. Split the other costs equally. Add utilities, internet, the shared part of groceries and other shared costs, then divide by the number of people.
4. Add the two parts. That is each person’s monthly total.

Each part is rounded to the cent, and leftover cents are handed out one at a time so the totals add up to the household bill exactly.

Worked example: three roommates

Say the rent is $2,380 and the three bedrooms are 140, 110 and 90 square feet, which is 340 in all. $2,380 ÷ 340 is $7 a square foot, so the rent shares are $980, $770 and $630.

The other shared costs for the month are $135 of utilities, $70 of internet, $220 of shared groceries and $25 of other costs. That is $450, and $450 ÷ 3 is $150 each.

Person	Rent	Other costs	Monthly total
Person 1 (140 sq ft)	$980	$150	$1,130
Person 2 (110 sq ft)	$770	$150	$920
Person 3 (90 sq ft)	$630	$150	$780

The three totals add up to $2,830, which is the $2,380 of rent plus the $450 of other costs. The 50 square feet between the biggest and smallest room is worth $350 a month in rent, and the shared costs do not change it.

What belongs in the other shared costs?

• Utilities. Electric, gas and water for the month. When the bill changes each month, use the latest one, or the average of the last three if you want a steady figure. If people are home for very different numbers of nights, the split utilities calculator divides the usage part of the bill by nights home instead.
• Internet. A flat monthly fee, so an equal split fits.
• Groceries, shared part only. Staples everyone eats. Food one person buys for themselves stays out, and the grocery bill split calculator separates the two when one receipt holds both.
• Other. Cleaning supplies, a shared streaming plan or anything else the household splits equally.

Common mistakes

• Putting shared rooms in the weights. Kitchens and living rooms are used by everyone, so only bedrooms get a weight.
• Weighing the utilities by room size. The weights are for rent only. This calculator keeps utilities, internet and groceries in the equal part.
• Mixing units. One room in square feet and another in points makes the shares meaningless. Pick one unit for every slot.
• Leaving a roommate’s weight in when they have moved out. Their rent share and their equal share both stay in the totals until the weight is set to 0.

Tracking the totals in EvenOut

In EvenOut, make a Household group and add the rent once as a “Shares” split, using the weights 140, 110 and 90 as the shares. Add the shared bills as “Split equally”. Rent and a fixed internet plan can be set to repeat monthly, and in this example the shares give the same rent column as the calculator.

The agreed rules belong in the roommate budget template, which lays out the month as a printable sheet. What expenses roommates should split explains which costs go in the equal part, and how to split utilities between roommates runs one month of bills through four rules.