A pro rata rent split divides the rent in proportion to what each person uses: days they occupied the flat, the size of their room, or both. An equal split assumes everyone's share is identical. When move-in dates or bedrooms differ, equal stops being fair and pro rata takes over.
The prorated rent calculator on this site turns this formula into a ten-second job.
Why rent splits go wrong
Most arguments start with a fixed total and no agreed rule. $1,800 a month split three ways is $600 each. Then one person moves in on the 15th, another has a room half the size of the rest, and $600 each feels wrong to everyone. Pro rata replaces the argument with arithmetic: each person pays for their actual share of days and space.
Method 1: split by days occupied
Use this when rooms are roughly equal and only move-in dates differ. You need the rent per day first.
- Monthly rent: $1,800
- Days in the month: 30, so the daily rate is $1,800 ÷ 30 = $60
- Anna lives there all 30 days and pays 30 × $60 = $1,800. Wait, that leaves nothing for Ben.
Correct way: total days billed across everyone is 30 (Anna) + 15 (Ben, from the 16th) = 45. Daily rate is $1,800 ÷ 45 = $40. Anna pays 30 × $40 = $1,200. Ben pays 15 × $40 = $600. Together $1,800, and Ben only pays for the half month he was there.
Method 2: split by room size
Use this when everyone lives there the full month but bedrooms differ. Add up the square meters (or square feet) of all private spaces, then each person pays rent × (their space ÷ total space).
- Rooms: 16 m², 12 m², 8 m². Total private space: 36 m²
- Rent: $1,800. Rate per m²: $50
- Payouts: $800, $600, $400
Shared areas like the kitchen usually stay out of the split, because everyone has equal access. If one flatmate has an en-suite bathroom, include it in their private space.
Method 3: combine days and size
This covers the messy real cases. Multiply each person's space by their days to get "room-days", then split by those.
- Anna: 16 m² × 30 days = 480 room-days
- Ben: 12 m² × 30 days = 360 room-days
- Cam: 8 m² × 15 days = 120 room-days
- Total: 960 room-days. Rate: $1,800 ÷ 960 = $1.875 per room-day
- Anna pays $900, Ben pays $675, Cam pays $225
Run the numbers yourself: enter the total rent and each share. The calculator does the division and rounding for you, free, no signup.
The rounding trap
When per-day or per-meter amounts come out with decimals, everyone rounds at the same time and the parts no longer add up to the total. Pick one person (usually the leaseholder) to absorb the leftover cents, and agree on it before money moves. Our guide on how to calculate pro rata shows the trap with a utility bill.
Related guides
Splitting utility bills pro rata How to calculate pro rata: formula and worked examples What does "pro rata" mean?Frequently asked questions
How do you split rent when someone moves in mid-month?
Bill by days: add up the days each person occupied the flat that month, divide the rent by that total, and multiply by each person's days. The person moving in on the 16th pays for 15 days in a 30 day month.
Should a couple count as one share or two?
For room size, one share (they share one bedroom). For utility usage, usually more than one share, since two people use more hot water and electricity. Agree on which split applies to which bill.
Is pro rata rent fair when rooms are different sizes?
It is the most defensible option: each person pays rent × (their room size ÷ total room size). Add an adjustment if someone gets an en-suite or balcony, since those change the value of the room.