Rent split calculator: split rent fairly by room size
When the bedrooms aren’t the same size, splitting rent equally means whoever has the box room is subsidising whoever has the big one. Splitting purely by floor area goes too far the other way, because everyone shares the kitchen, living room and bathroom equally. This calculator does both: part of the rent is shared equally, the rest follows the size of each bedroom.
| Who | Bedroom size (m² or sq ft) | |
|---|---|---|
- Ana 38.89%£933.33
- Ben 33.33%£800.00
- Cat 27.78%£666.67
How the calculation works
- Decide how much of the rent pays for space you all share. That part is split equally.
- The rest is split in proportion to each bedroom’s floor area.
- Each person’s share is their equal part plus their room part. Amounts are rounded to the penny and always add up to the full rent.
Worked example: three flatmates, £2,400 a month
Ana’s room is 16 m², Ben’s is 12 m² and Cat’s is 8 m², 36 m² in total. They agree half the rent is for shared space.
- Shared half: £1,200 split three ways is £400 each.
- Room half: £1,200 by area. Ana gets 16/36 of it (£533.33), Ben 12/36 (£400.00), Cat 8/36 (£266.67).
- Totals: Ana pays £933.33, Ben £800.00 and Cat £666.67. That’s £2,400 exactly.
For comparison, an equal split is £800 each, so Cat would be paying £133 a month for space Ana has. Splitting purely by area would put Cat at £533.33 and Ana at £1,066.67, which charges Ana twice as much for the same kitchen.
Choosing the shared percentage
There’s no official number; it’s whatever your household thinks is fair. Measuring helps: add up the floor area of the shared rooms and see what fraction of the whole home they are. If the kitchen, living room and bathroom are 40% of the flat, 40% shared is easy to defend. If you can’t measure them, 50% is a reasonable starting point to agree on.
Then track it without spreadsheets
Once you’ve agreed the split, make a FayrShare group for the flat and add the rent with a percentage split, using the percentages above (to two decimal places, which is the precision FayrShare takes). Add bills and the shared shop as they come, usually split equally, and FayrShare works out who owes whom in the fewest payments. It’s free, with no limit on expenses.
Questions
Should I measure in square metres or square feet?
Either. Only the sizes relative to each other matter, so use the same unit for every room.
What shared percentage should we use?
Half is a sensible default when the kitchen, living room and bathroom are a big part of the home. Go lower if the shared space is small or nobody uses the living room; go higher if the bedrooms are all roughly similar and you mostly live in the shared rooms.
What about an en-suite or a room with a balcony?
Room size doesn’t capture everything. Agree a small top-up for the better room, say a few percentage points, and take it off the others’ shares equally. FayrShare’s percentage split lets you type exactly those numbers.
Do bills get split the same way?
Usually not. Most flatmates split energy, broadband and council tax equally, because everyone uses them about the same. Use an equal split in FayrShare for those.