What this calculator does
Find out what each roommate should pay, down to the cent. An equal split is simple, but it isn't always fair. One person may have the big bedroom, or incomes may be very different. So this calculator gives you three ways to divide the rent. You can split it equally, by bedroom size, or by each person's income.
The room-size method can also count shared space. Enter the size of the whole home, and the kitchen, living room and hallways are shared equally. Every square foot then costs the same. Whatever method you pick, the amounts are rounded to the cent. They're rounded so they add up to exactly the rent, and nobody has to cover a stray penny.
Where it's used
Why this math matters outside the classroom:
- Moving in together. Three roommates split $2,400 for a 900 sq ft apartment at $2.67 per sq ft, paying $897.78, $791.11 and $711.11.
- Couples by income. Partners earning $60,000 and $40,000 split $2,000 rent as 60% and 40%, paying $1,200 and $800.
- Ratio problems. Students divide $2,000 in the ratio 200 : 100 : 100 and get $1,000, $500 and $500.
- Student housing. Students in a shared house compare equal and size-based splits before signing a lease together.
- Landlord listings. Room-by-room landlords price bedrooms so the room rents add up to the whole-home rent they want.
Grade level and standards: Grades 6–7; Common Core State Standards for Mathematics 6.RP.A.3, 7.RP.A.3. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Enter the total monthly rent.
- Choose how to split it: equally, by room size or by income.
- For room size, list each bedroom's size in order. Add the size of the whole home if you know it. For income, list each person's income in order.
- Read each person's rent. The table shows the area or income behind each share.
What the inputs mean
- Bedroom sizes (sq ft or m²)
- Measure each bedroom's floor area (length × width). Any unit works, as long as every room and the whole home use the same one.
- Whole home size (same unit)
- The whole home's floor area. The space outside the bedrooms is divided equally, since all roommates use it. Leave it blank to split by bedroom size alone.
- Incomes ($)
- Use the same kind of income for everyone, such as yearly take-home pay. A person with no income pays nothing under this method. So some households set a minimum share instead.
Formula and method
equal: rent ÷ number of people shared space = whole home − sum of bedrooms your area = your bedroom + shared space ÷ number of people your rent = rent × your area ÷ whole home by income: your rent = rent × your income ÷ total income amounts are rounded to the cent so they add up to the rent exactly
Splitting by area gives every square foot the same price. Each person pays for their own bedroom, plus an equal slice of the space everyone shares. Without a whole-home size, only bedrooms are counted. That makes the gaps between shares larger.
Splitting by income makes each person's rent the same fraction of their income. Some households find that fairer when earnings differ a lot.
Rounding each share on its own could leave the total a cent or two off the rent. So the calculator rounds every share down first. Then it hands the leftover cents to the shares that were closest to rounding up.
Worked example
Three roommates share a 900 sq ft apartment that rents for $2,400 a month. The bedrooms are 180, 140 and 110 sq ft.
- Shared space: 900 − (180 + 140 + 110) = 470 sq ft, which is 156.67 sq ft each.
- Each person's area, bedroom plus shared slice: 336.67, 296.67 and 266.67 sq ft.
- Rent per sq ft: $2,400 ÷ 900 = $2.6667.
- Rent: 336.67 × $2.6667 ≈ $897.78, 296.67 × $2.6667 ≈ $791.11 and 266.67 × $2.6667 ≈ $711.11.
Result: Person 1 pays $897.78, Person 2 pays $791.11 and Person 3 pays $711.11. That adds up to exactly $2,400.00.
Understanding the result
The biggest room costs the most. But it costs less than its size alone would suggest, because everyone pays equally for the shared space.
Room size is only one measure of value. A private bathroom, a balcony or a parking space can be worth more than a few extra square feet. So groups often adjust the result by an amount they agree on.
Whatever method you use, agree on it before anyone moves in. Then write it down.
Assumptions and limitations
- Every square foot of the home, in bedrooms and shared areas, is worth the same.
- Shared space is used equally by everyone.
- Incomes, if used, are on the same basis for everyone.
- Private bathrooms, windows, closets and other features aren't given their own value.
- Utilities and other shared bills aren't included. The shared expenses calculator can settle those.
- Couples sharing a room aren't handled automatically. Enter them as one person, then split their part between them.
Frequently asked questions
What is the fairest way to split rent?
There's no single answer. Equal splits are simplest and suit similar rooms. Splitting by area suits rooms of different sizes. Splitting by income suits partners or friends with very different earnings. The best method is the one everyone agrees to in advance.
Should shared space be split equally?
Usually, yes, because everyone uses the kitchen and living room. If you count only bedrooms, the person with the biggest room also pays more for the shared space. That can feel unfair when the rooms are close in size.
How do I handle a room with a private bathroom?
One option is to add the bathroom's area to that person's bedroom size. Another is to agree on a fixed monthly extra charge. Subtract it from the rent and split the rest. Then add it back to that person's share.
Why does one person pay a cent more?
When rent doesn't divide exactly, someone has to cover the leftover cent. The calculator gives it to the person whose exact share was closest to the next cent. So everyone is within a cent of their exact share, and the total comes out exact.
How this calculator is checked
Method: Proportional division by bedroom area (with shared area divided equally), by income, or equally; largest-remainder rounding to the cent. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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