Rent Split Calculator

What this calculator does

The rent split calculator divides monthly rent and any shared utilities between roommates. It supports the four splitting methods that come up most often in roommate conversations: an equal split, a split proportional to income, a split proportional to room size, or a custom percentage split for any private arrangement.

How the rent split calculator works

Pick the mode that matches your household, enter the rent and any shared utilities, and provide the per-person inputs the mode requires:

• Split evenly: enter the number of roommates. The total is divided equally.
• Split by income: enter each roommate's monthly income. The total cost is divided proportionally to income shares.
• Split by room size: enter each room's square footage. The rent is divided proportionally to room size; shared utilities are split evenly.
• Custom percentage: enter each person's share as a percentage. The calculator applies the percentages to the total cost and warns if the percentages do not add up to 100.

Even split

The simplest method: every roommate pays the same amount. With $2,400 rent, $150 utilities, and 3 roommates, the total is $2,550 and each person pays $2,550 / 3 = $850. This works well when rooms are similar in size and quality and incomes are roughly comparable.

Split by income

When one roommate earns substantially more, splitting proportionally to income keeps the rent burden roughly equal as a percentage of income. With rent + utilities of $2,550 and incomes of $4,000 and $6,000:

• Total income: $10,000.
• Person A: $2,550 × 4,000 / 10,000 = $1,020 (40% of the cost).
• Person B: $2,550 × 6,000 / 10,000 = $1,530 (60% of the cost).

Both pay roughly 25.5% of their monthly income on rent and utilities, which is the point of this method.

Split by room size

When rooms are noticeably different sizes, splitting rent by square footage is a clean way to charge each person for what they actually use. Shared utilities are typically split evenly because internet, heat, and electricity benefit both rooms equally. With $2,400 rent, rooms of 140 sq ft and 180 sq ft (total 320), and $150 utilities:

• Person A rent: $2,400 × 140 / 320 = $1,050.
• Person B rent: $2,400 × 180 / 320 = $1,350.
• Utilities each: $150 / 2 = $75.
• Person A total: $1,125. Person B total: $1,425.

The room-size method usually rewards giving up some square footage in exchange for a lower monthly bill, which is often the goal when one roommate values space more.

Custom percentage

Custom mode lets you encode any agreement. Common reasons to use it: a roommate has a private bathroom or balcony, one person stores significantly more in shared spaces, one room has a closet the other does not, or the lease dictates an unusual division. With $2,400 + $150 utilities ($2,550 total) at 40% / 60%:

• Person A: $2,550 × 40 / 100 = $1,020.
• Person B: $2,550 × 60 / 100 = $1,530.

If the percentages do not add up to 100, the calculator shows a warning so you can fix the inputs. Sub-totaling by hand is also worth doing as a sanity check whenever the percentages are not standard.

Which method should you pick?

• Even split if rooms are similar and incomes are close.
• By income if incomes differ significantly and the household wants the rent burden to be roughly equal as a percentage of income.
• By room size if rooms vary noticeably in size and the household wants each person to pay for the space they get.
• Custom percentage if a private amenity, lease quirk, or other agreement makes the first three methods feel off.

The best approach is usually a short conversation up front: agree on the method before signing the lease and write it into a short roommate agreement so everyone knows the answer the same way.

Worked examples

• Even split, 3 roommates, $2,400 rent + $150 utilities: each pays $850.
• By income, $4k / $6k incomes, $2,550 total: A pays $1,020, B pays $1,530.
• By room size, 140 / 180 sq ft, $2,400 rent: A pays $1,050 rent, B pays $1,350 rent; utilities split evenly on top.
• Custom, 40% / 60% on $2,550 total: A pays $1,020, B pays $1,530.
• By income, 3 roommates, $3k / $4k / $5k on $3,000 total: A pays $750, B pays $1,000, C pays $1,250 (proportional to income).

Common mistakes

• Choosing a method without discussing it with all roommates first. The math is easy; the agreement is the part that prevents disputes later.
• Forgetting to include all the shared bills. Internet, electricity, water, gas, and any subscription services that the whole household uses should typically be grouped under utilities.
• Treating room size as the only consideration when one room has a clear amenity advantage (private bathroom, walk-in closet, balcony). Consider a custom split or a small premium in those cases.
• Custom percentages that do not add up to 100. The calculator warns you, but it is easy to miss the warning if you only glance at the per-person numbers.
• Forgetting that prorated rent comes up for move-in and move-out months. See the prorated rent calculator for the partial-month math.

Related tools

• Prorated rent calculator for partial-month rent at move-in or move-out.
• Rent increase calculator for the math behind a rent change: new rent, percentage change, or annual cost.
• Percentage calculator for the percent math underlying income and custom splits.
• Savings calculator for setting aside money toward a deposit or first month's rent.
• Date calculator for counting days between lease milestones.
• All money calculators.