RoomProrateSplitting the first bill when roommates moved in on different dates
Updated 2026-11-01
The situation comes from the same r/Roommates question (October 2026): a six-person house where everyone moved in on a different day. The amounts are a fictional bill run through the RoomProrate calculator on 1 November 2026.
At the start of a lease, or when a house fills up room by room, the first bill often covers people who arrived days or weeks apart. Splitting it six ways equally would charge the last person in for weeks they did not live there.
Worked example: six move-in dates
September electricity, 1 to 30 September (30 days): usage 150.00 and a fixed charge of 30.00, shared equally by all six. Ari and Bo moved in on 1 September, Cam on the 5th, Dee on the 10th, Eli on the 15th and Sam on the 20th. Nobody moved out.
| Person | Days | Daily split | Person-days |
|---|---|---|---|
| Ari | 30 | 43.75 | 38.58 |
| Bo | 30 | 43.75 | 38.58 |
| Cam | 26 | 33.75 | 34.11 |
| Dee | 21 | 25.42 | 28.51 |
| Eli | 16 | 19.17 | 22.91 |
| Sam | 11 | 14.16 | 17.31 |
If you type this bill into the calculator yourself, a share that ties on rounding can come out 0.01 different, because the leftover cent goes by the calculator's internal order of people. The total does not change.
Why the two columns differ
Usage is 5.00 a day. With the daily split, the first four days are shared by Ari and Bo alone, 2.50 each per day. From 20 September six people share each day, 0.83 each. So the people who arrived first carry more of the early days.
With person-days, the six stays add up to 134 person-days, and each person pays their days out of 134 of the 150.00. Sam's 11 days give 12.31 of usage, plus 5.00 fixed. Both columns add up to 180.00; the calculator settles the odd cents by its fixed rounding rule (see rounding).
The fixed charge on a first bill
The example shares the 30.00 fixed charge equally, because everyone was on the lease for September. Two other agreements are common:
- Only people living there share it. Here that changes nothing, because everyone was there by the end of the bill.
- The fixed part follows days too. Leave fixed blank and enter 180.00 as usage. With the daily split that gives Ari 46.50, Bo 46.50, Cam 34.50, Dee 24.50, Eli 17.00 and Sam 11.00.
Pick one for the whole lease, not bill by bill. For the difference between the methods in a simpler case, see daily split and person-days.
Questions
Do roommates who move in later pay the full fixed charge?
Only if you agree that they do. RoomProrate splits the fixed charge equally among the people you tick for that bill. In the example, ticking all six gives each 5.00. If the fixed part should follow days instead, add it to usage and leave fixed blank: the latest arrival then pays 11.00 instead of 14.16.
Which method is fairer when people move in on different dates?
Neither is the single fair answer. The daily split charges each day to whoever lived there that day, so the first people in pay more for the first quiet days. Person-days shares the whole bill by days present, so later arrivals pay a little towards days before they came. In the example the latest arrival pays 14.16 or 17.31.
See all guides.