January's gas or electric bill lands, and it is much bigger than July's. Same flat, same people, same thermostat. Now the group chat asks who turned it up.
Often nobody did. Heating is seasonal. The better question is how to pay a bill that swings all year.
Three ways to pay
1. Actual bill each month. Accurate, but winter shares are far bigger than summer ones.
2. A level amount. Add up a year of bills, divide by 12 and everyone pays that every month. The account holder uses summer surplus to cover winter. Ask your utility if it offers level billing too.
3. Actual bill by who lived there. Split each month among the people home that month. Use this when people move in or out.
The catch with a level amount
It is only fair if the same people stay all twelve months. If someone leaves in March and a newcomer arrives in April, the leaver paid small level shares for the cold months and the newcomer pays for cold months that are over. So level it, then true it up.
Worked example (illustrative numbers)
Three seats. Gas bills: Jan $180, Feb $150, Mar $100, Apr $60, May $30, Jun $20, Jul $20, Aug $20, Sep $30, Oct $50, Nov $90, Dec $150. The year totals $900.
Level amount. $900 / 12 = $75 a month, so $25 each.
Ana and Cam stay all year. Their real share is $900 / 3 = $300, and they paid 12 x $25 = $300. Square.
Ben holds the third seat January to March. Dee takes it from April.
- Jan to Mar bills: $430. Ben's real share: $143.33. He paid 3 x $25 = $75, so he owes $68.33.
- Apr to Dec bills: $900 - $430 = $470. Dee's real share: $156.67. She paid 9 x $25 = $225, so she is owed $68.33.
Ben pays Dee $68.33. The seat totals $143.33 + $156.67 = $300, same as Ana and Cam.
| Paid in | Real share | Settle | |
|---|---|---|---|
| Ana | $300 | $300 | $0 |
| Cam | $300 | $300 | $0 |
| Ben | $75 | $143.33 | owes $68.33 |
| Dee | $225 | $156.67 | gets $68.33 |
These numbers are made up; use your own bills.
Keep the true-up simple
- Do it whenever someone joins or leaves, not at year end.
- Use the actual bills for the months each person lived there.
Do the math faster
The utility bill splitter takes each person's days at home. Free, no signup.
FAQ
Is a level amount better than the actual bill? Easier on budgets, if the same people stay all year. If the group changes, add a true-up.
What if one roommate heats their own room? Take that personal use out first, as in the guide on electricity and heavy appliances, then smooth the rest.
What if the year's total differs from our level amount? Settle the difference by seat, the same way as the example.
Keep it friendly, keep it written
Billmates is a web app, still on the waitlist, that tracks who owes what in a shared home. It never holds or moves your money. You pay each other the way you already do. Roommates join from a browser link. No ads. Leave your email to hear when it's ready.