How to split rent, by hand and by calculator
All four methods worked through on a real flat, the shared-space correction most people forget, and how to sanity-check any answer you get.
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How this differs from an even split. Each row shows what that person pays versus an even split — switch between the four buttons above and watch the numbers move. Bigger private rooms cost more, and shared space costs everyone the same; that is the whole principle behind the by-room method. The shares always add up to the total rent exactly; if they ever don't, the tool says so. This calculator divides rent between the people you list — it is not legal or tenancy advice, and a rent split is whatever the people signing the lease agree to.
Worked example: three roommates, $3,000 rent
The arithmetic behind each method is short enough to check by hand. Splitting evenly is the total rent divided by the number of people. Splitting by room size adds an equal share of the common area to each private room, then divides rent by each person's effective area — with three rooms of 180, 150 and 120 square feet and 300 square feet of shared space, the shared space becomes 100 square feet per person, so effective areas are 280, 250 and 220 out of 750, giving $1,120, $1,000 and $880 on a $3,000 flat.
Splitting by income divides rent by each person's share of the household income — with incomes of $80,000, $60,000 and $40,000 out of $180,000, a $3,000 rent becomes $1,333.33, $1,000.00 and $666.66. The weighted method takes half of each: the room-size share and the income share are averaged, which lands the same three people at $1,226.66, $1,000.00 and $773.33. Notice that the middle roommate pays exactly $1,000.00 under three of the four methods, which is a useful sanity check when you are testing a split.
| Split evenly | By room size | By income | Room + income | |
|---|---|---|---|---|
| Roommate A $80,000 · 180 sq ft | $1,000.00 | $1,120.00 | $1,333.33 | $1,226.66 |
| Roommate B $60,000 · 150 sq ft | $1,000.00 | $1,000.00 | $1,000.00 | $1,000.00 |
| Roommate C $40,000 · 120 sq ft | $1,000.00 | $880.00 | $666.66 | $773.33 |
Roommate B pays exactly $1,000.00 under three of the four methods, which is a useful check when you are testing a split yourself: if the middle person lands somewhere far from the middle number, something in the arithmetic is wrong.
The shared-space correction
Common areas are the part people forget. The kitchen, living room and bathroom are used by everyone equally, so charging purely by private room size would mean the smallest room pays the least for the space everyone shares. Adding an equal slice of the common area to each person's private area corrects this, and it is why the by-room method on this page asks for the shared square footage separately.
If you do not know your exact areas, measure or estimate — the split is not sensitive to small errors. A rough measurement of the private rooms and a rough guess at the shared space will land within a few dollars of the exact answer, and the principle, that bigger private space costs more while shared space costs everyone the same, is what actually matters.
Choosing between the methods
There is no single correct answer here, and the calculator will not pretend otherwise. The even split is the right choice when the rooms are genuinely comparable and everyone earns roughly the same — it takes ten seconds to explain and nobody has to think about it again for a year. The room-size split is the right choice when rooms differ, which is almost always the real disagreement in a shared flat. The income split is the right choice when people earn very different amounts and the group cares about equal burden rather than equal dollars.
The weighted method exists because many groups cannot agree between the last two, and averaging them is a defensible way to stop the argument. Try all four on your own numbers above — they take seconds — and notice which ones put someone in an uncomfortable position. That discomfort is usually the actual conversation you need to have, and having the number on screen makes it far easier to have it before the lease is signed rather than after.
