Rent split calculator

What is a rent split calculator?

A rent split calculator divides one monthly rent bill among the people sharing the home. Splitting evenly is the obvious starting point, but it is rarely the only fair answer: one roommate may earn twice as much as another, and the person in the cramped back bedroom is not getting the same apartment as the person with the large room and the private bathroom. This calculator supports the three splits people actually use — evenly, in proportion to income, and in proportion to room size — and shows what each roommate owes every month, along with the percentage of the rent they are covering.

Because the whole point is to settle an argument, the calculator also adds the shares back up. If the shares sum to the rent you entered, nobody is quietly overpaying or underpaying, and the household knows the numbers add up before anyone transfers money.

How does the calculator work?

You enter the total monthly rent, choose a split method, and then add one row per roommate. Each row takes an optional name, which is used to label the results; if you leave it blank, the roommate is simply listed as “Roommate 1”, “Roommate 2”, and so on. Rows can be added or removed, so the calculator works for two roommates or for six.

What the row asks for next depends on the method you picked. An even split needs nothing more than the number of rows. A split by income asks each roommate for their monthly income. A split by room size asks for the floor area of each private room. The calculator turns whichever value you supply into a weight, then divides the rent in proportion to those weights, so a roommate with twice the income (or twice the floor area) of another pays twice as much.

Room size deserves one note. Only the ratio of the rooms matters, never the unit they are measured in, because the unit appears in both the top and the bottom of the fraction and cancels out. Rooms of 200, 150 and 100 square feet produce exactly the same split as the same rooms measured as 18.58, 13.94 and 9.29 square metres. Use whichever unit you like, as long as every roommate uses the same one.

Formulas

Let $R$ be the total monthly rent and $n$ the number of roommates.

For an even split, every roommate pays the same amount:

$S_i = \frac{R}{n}$

For a split by income, let $I_i$ be roommate $i$‘s monthly income. Each share is the rent scaled by that roommate’s slice of the household’s total income:

$S_i = R \times \frac{I_i}{\sum_{k=1}^{n} I_k}$

For a split by room size, let $A_i$ be the floor area of roommate $i$‘s room. The rent is scaled by that room’s slice of the total private floor area:

$S_i = R \times \frac{A_i}{\sum_{k=1}^{n} A_k}$

In every method the weights are normalised by their own sum, so the shares always add back up to the rent:

$\sum_{i=1}^{n} S_i = R$

Worked example

Three roommates share an apartment renting for 3,000 per month.

Split evenly, each of the three pays $\frac{3000}{3} = 1000$ per month.

Now split by income. The roommates earn 5,000, 4,000 and 3,000 per month, so the household earns $5000 + 4000 + 3000 = 12000$ in total. The shares are:

$S_1 = 3000 \times \frac{5000}{12000} = 1250$

$S_2 = 3000 \times \frac{4000}{12000} = 1000$

$S_3 = 3000 \times \frac{3000}{12000} = 750$

The three shares are 1,250, 1,000 and 750, covering 41.7%, 33.3% and 25.0% of the rent, and they total $1250 + 1000 + 750 = 3000$ — exactly the rent. The highest earner pays 250 more than under an even split, and the lowest earner pays 250 less.

Finally, split the same 3,000 by room size, with private rooms of 200, 150 and 100 square feet, a total of 450. The shares work out to $3000 \times \frac{200}{450} = 1333.33$, $3000 \times \frac{150}{450} = 1000$ and $3000 \times \frac{100}{450} = 666.67$. The roommate with the largest room pays roughly twice what the roommate in the smallest room pays.

Practical notes

Shares are rounded to two decimals, so a rent that does not divide cleanly can leave a gap of a cent or two between the sum of the shares and the rent itself. Splitting 1,000 three ways gives 333.33 each, which totals 999.99. The “sum of all shares” line exists so you can spot this immediately; households usually settle it by having one person round up, and rotating who does so.

An income split is a decision about fairness, not a rule. It means the roommate earning the most subsidises the roommate earning the least, which some households consider obviously right and others consider nobody’s business. Agree on the principle before you run the numbers, and be aware that using income requires everyone to disclose what they earn. If you want to keep incomes private but still avoid a flat split, room size is the usual compromise: it is objective, easy to measure, and reflects what each person is actually getting.

Room size also does not capture everything about a room. A private bathroom, a balcony, more windows, or being at the quiet end of the hallway all have value that square footage misses. A common approach is to run the room-size split first, then adjust it by hand — for instance, adding a fixed amount to the share of whoever has the ensuite. Shared costs like utilities, internet, and cleaning supplies are usually split evenly even when the rent is not, since everyone uses them about equally. Whatever you decide, write it down: most roommate disputes come from a vague verbal agreement, not from the arithmetic. If you are still deciding whether the apartment fits your budget at all, check your share against the rent affordability calculator.

FAQs

Is an even split or an income split fairer?

There is no universal answer. An even split treats the apartment as a shared good that everyone uses equally, and it is simple and private. An income split treats rent as a proportion of what each person can afford, which keeps a lower earner from being priced out of the household. Neither is more “correct” — what matters is that everyone agrees to the method before signing the lease.

How do we handle a couple sharing one room?

The simplest approach is to treat the couple as one roommate: enter one row, one room, and one combined income if you are splitting by income. That keeps the split in line with what the household is actually buying, which is a room. Some households instead charge a couple slightly more than a single occupant of the same room, on the grounds that two people put more wear on the shared space and use more utilities; if you do that, agree on the surcharge separately from the rent split itself.

The shares do not add up to exactly the rent. Why?

Rounding. Each share is rounded to the nearest cent, and those roundings do not always cancel out — 1,000 split three ways is 333.33 each, and three of those total 999.99, a cent short. The calculator shows the sum of all shares precisely so this gap is visible. Have one roommate cover the difference, or rotate it month to month.