Rent Split Calculator (roommates: equal, by room size or by income)

Understanding the rent split calculator — concept and principle

Sharing a home raises an awkward question: who pays what? This calculator divides rent among up to four housemates equally, by bedroom size, by income, or with a mixed method that splits shared space equally and private space by room size. Shared bills are always divided equally.

$1,500 is split equally, $1,500 by bedroom size (14:11:9) and the $240 of bills equally: total $3,240.

How it is calculated

Everyone with a bedroom size above 0 is counted.
Each person's share of the rent = their weight ÷ the sum of all weights.
Weights: 1 each for an equal split; bedroom size for a split by room; monthly income for a split by income.
Mixed method: half the rent is split equally (for the kitchen, bathroom and living room), half in proportion to bedroom size.
Each person pays their rent share + shared bills ÷ number of people.

The principle

There is no legal formula; the aim is a split everyone sees as fair. Splitting by bedroom size charges more to whoever gets more private space. But much of the rent pays for space everyone uses equally, so a pure size split can overcharge the person with the big room. The mixed method recognises both: shared areas benefit everyone the same, private rooms do not. Income-based splits reflect ability to pay, which some couples and families prefer.

Worked example

Default inputs: rent 3,000 USD, shared bills 240 USD, mixed method, bedrooms 14, 11 and 9 (person 4 empty).

People sharing = 3. Equal half = 1,500 ÷ 3 = 500 USD each; bills = 240 ÷ 3 = 80 USD each.
Size half: total size = 34. Person 1 = 1,500 × 14 ÷ 34 ≈ 617.65 USD; person 2 ≈ 485.29 USD; person 3 ≈ 397.06 USD.
Person 1 pays 500 + 617.65 + 80 = 1,197.65 USD.
Person 2 pays 1,065.29 USD; person 3 pays 977.06 USD; person 4 —.
Total per month = 3,240.00 USD, matching rent plus bills.

Each point is the calculator re-run with only “Total rent per month” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Total rent per month	Person 1 pays
750	$359.41
1,500	$638.82
2,250	$918.24
3,000	$1,197.65
3,750	$1,477.06
4,500	$1,756.47
6,000	$2,315.29

How to read the result

If one room has a private bathroom, a balcony or much better light, consider adding to its size or agreeing an extra amount, because size alone may not capture its value. Revisit the split if someone moves out or a room changes use.

Common mistakes

Mixing square metres and square feet between rooms.
Including shared space in a bedroom's size.
Forgetting to agree how bills that vary with use (heating, electricity) will be shared.
Changing the method without everyone's agreement.

Keep in mind: The result is a suggestion for discussion, not a legal requirement. Each person may still be jointly responsible for the full rent under the lease.

Frequently asked questions

What is the fairest way to split rent?

There is no single answer. Many housemates use the mixed method, which splits shared space equally and private space by room size.

Should a bigger room pay more?

Usually yes, because that person has more private space.

Can couples count as one person?

You can treat them as one room with a larger weight, or agree a fixed premium for two occupants.

Sources: Gal, Mash, Procaccia & Zick (2017). Which Is the Fairest (Rent Division) of Them All? Journal of the ACM, 64(6). · Su, F. E. (1999). Rental Harmony: Sperner's Lemma in Fair Division. American Mathematical Monthly, 106(10).

Checked 9 Nov 2026. Proportional allocation: each share = weight ÷ sum of weights (equal, bedroom floor area or income). Our own method summary; no statutory rule applies to splits between housemates.

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