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Six monthly bills, two kinds. Rent, renters insurance and internet are the same figure every month whether anyone is home or not; electricity, water and gas move with the meter and the headcount. This page splits all six in one table, then gives each room two numbers: the fixed part that never moves, and the moving part that follows the meter — plus the most the month can cost.
What Room 1 owes this month — and how much of it never moves
Fixed $651.01 · Moving $110.77 — $2,184.00 across 6 bills. The fixed lines are the same figure next month.
One row per room. People in this room drives the water and gas lines — put 2 in a room a couple shares. Electricity units drives the electricity line; leave it blank and that bill falls back to an equal split.
Each bill is divided and rounded on its own, so its shares add back up to that bill exactly; the fixed and moving shares are then added up per room.
Three views of the same flat: the fixed part against the moving part, what a doubled meter does to each, and what the fixed part commits you to over twelve months.
The table above prints the answer; this one prints the sum that produces it. Same flat, same six bills, same three rooms — every line here can be checked against the bills in your hand and the meter reading. The class column is the point of the page: three lines are fixed and three move, and the totals at the bottom keep the two classes apart.
| Line | Class | Divided on | Bill | Room 1 | Room 2 | Room 3 |
|---|---|---|---|---|---|---|
| Rent | Fixed | per room, three rooms | 1,850.00 | 616.671,850.00 ÷ 3, + leftover cent | 616.671,850.00 ÷ 3, + leftover cent | 616.661,850.00 ÷ 3 |
| Renters insurance | Fixed | per room, three rooms | 24.00 | 8.0024.00 ÷ 3 | 8.0024.00 ÷ 3 | 8.0024.00 ÷ 3 |
| Internet | Fixed | per room, three rooms | 79.00 | 26.3479.00 ÷ 3, + leftover cent | 26.3379.00 ÷ 3 | 26.3379.00 ÷ 3 |
| Electricity | Moving | by units, 420 / 300 / 180 of 900 | 142.00 | 66.27420 × 0.1578, + leftover cent | 47.33300 × 0.1578 | 28.40180 × 0.1578 |
| Water | Moving | by headcount, 2 / 1 / 1 | 58.00 | 29.0058.00 ÷ 4 × 2 people | 14.5058.00 ÷ 4 | 14.5058.00 ÷ 4 |
| Gas | Moving | by headcount, 2 / 1 / 1 | 31.00 | 15.5031.00 ÷ 4 × 2 people | 7.7531.00 ÷ 4 | 7.7531.00 ÷ 4 |
| Fixed subtotal | never moves | rent + insurance + internet | 1,953.00 | 651.01616.67 + 8.00 + 26.34 | 651.00616.67 + 8.00 + 26.33 | 650.99616.66 + 8.00 + 26.33 |
| Moving subtotal | follows the meter | electricity + water + gas | 231.00 | 110.7766.27 + 29.00 + 15.50 | 69.5847.33 + 14.50 + 7.75 | 50.6528.40 + 14.50 + 7.75 |
| Each room's month | both classes | fixed + moving | 2,184.00 | 761.78651.01 + 110.77 | 720.58651.00 + 69.58 | 701.64650.99 + 50.65 |
| Over 12 months | the monthly figure, twelve times | nothing renegotiated | 26,208.00 | 9,141.36761.78 × 12 | 8,646.96720.58 × 12 | 8,419.68701.64 × 12 |
Three of the six lines need a rounding rule, and three divide to the exact cent. Rent at 1,850.00 ÷ 3 is 616.6667 a room: the three floors come to 1,849.98 and the two leftover cents go to the first two rooms, whose fractions tie at .667 — 616.67 / 616.67 / 616.66. Internet at 79.00 ÷ 3 is 26.3333: one cent is left and all three fractions tie, so Room 1 takes it — 26.34 / 26.33 / 26.33. Electricity divides by the units, and Room 1's fraction of .667 is the largest, so its 66.26 floor becomes 66.27. Insurance at 8.00 a room, water at 29.00 / 14.50 / 14.50 and gas at 15.50 / 7.75 / 7.75 land on whole cents with nothing left over. Every line's shares add back up to that line exactly, so the room columns add back up to 2,184.00 to the penny.
The gap between the largest and smallest room is $60.14 a month. The fixed part of that gap is $0.02 — the three fixed lines are within two cents of each other in every room, because rent, insurance and internet divide the same way for everyone. The moving part of the gap is $60.12: 37.87 of it from electricity, 14.50 from water and 7.75 from gas. In other words, almost everything that makes one roommate's month heavier than another's comes from the lines that can be measured, and almost nothing comes from the lines that cannot.
That is the practical case for the two-class split. A rule about the fixed lines is a rule nobody has to re-open: those three bills will be the same next month, so the decision is made once and the arithmetic just repeats. The moving lines are where the month actually varies, so that is where the conversation belongs — and it is a conversation about numbers on a meter, not about whether somebody is being fair.
A rent increase of $50.00 takes the rent line to 1,900.00, which divides into 633.34 / 633.33 / 633.33. Each room's fixed part rises by 16.67, 16.66 and 16.67 — 651.01 to 667.68, 651.00 to 667.66, 650.99 to 667.66 — and the moving part does not change by a cent. The month goes from 2,184.00 to 2,234.00, and the spread between rooms stays where it was, at two cents. A fixed increase is the fair kind of increase: it lands on everybody at once, in the same proportion, and it does not create a new argument.
The opposite case: usage doubles while the rate holds at 0.1578 a unit, so the electricity bill doubles from 142.00 to 284.00. The fixed column is identical — 651.01 / 651.00 / 650.99, a change of 0.00 in every room — while the moving column rises to 177.03 / 116.92 / 79.05. The months become 828.04 / 767.92 / 730.04, up 66.26, 47.34 and 28.40, in proportion to the 840 / 600 / 360 units. This is why the meter reading is worth keeping: it turns "the electricity bill went up" into three exact numbers, and each of those numbers belongs to a room that can see its own figure on the dial.
Write down three things and the rest of the year is arithmetic. Which lines are fixed and which move — on this page rent, renters insurance and internet are fixed and the other three move. What the moving lines follow, which here is the electricity meter at 0.1578 a unit and the headcount for water and gas. And what happens to each class when something changes: a fixed rise spreads over every room in proportion to rooms, and a usage rise spreads in proportion to units. With those settled, a new bill is one line of new arithmetic rather than a new negotiation.
The monthly household bill page runs the same six bills as one monthly figure per room; this page starts one step earlier and splits the month into the part that is settled and the part that is read. The utility split calculator takes any set of utility bills with a basis each, and the how to split rent page runs one rent through three rules at once. The leftover cent page covers the rounding rule this page uses on rent, internet and electricity, and the split by percentage page handles weighted bases when a flat wants one rather than a class. Every calculator runs the same integer-cent arithmetic, so a figure here can be checked against the same figure on another page.
A bill that is the same figure whether the flat is full or empty: rent, renters insurance and the internet line. The test is the repetition — if nobody were home for a month, those three would still arrive at the same amount. Electricity, water and gas are the opposite kind: they move with the meter and the headcount, so they belong to the moving class and get re-read every month.
Per room. Rent is charged for the space, renters insurance is one policy per address, and the internet line is one connection per flat — so each of the three divides by rooms, not by people. Water and gas are the lines that follow people, which is why a room with a couple in it carries two shares of those two lines while still carrying one room's share of rent, insurance and internet.
Because it is the fixed line people forget, and forgetting it means a cent-short argument every month. At 24.00 a month split three ways it is 8.00 a room — 96.00 a room over a year — and it is fixed, so it divides the same way every month. It is also the line that makes the fixed class complete: without it the fixed column is missing a bill that will certainly arrive.
The fixed part rises for every room in the same proportion and the moving part does not move. A rent rise of 50.00 takes rent to 1,900.00, which divides into 633.34 / 633.33 / 633.33, so each room's fixed part goes up by 16.67, 16.66 and 16.67 and the month goes from 2,184.00 to 2,234.00. The spread between rooms stays at two cents, because a fixed rise lands on everybody at once.
By reading, not by negotiating. Electricity divides by the units on the meter — 142.00 across 900 units is 0.1578 a unit, and each room's share is its units times that rate. Water and gas divide by headcount. That is the only part of the month that has to be re-run, and it is re-run with numbers anyone can check on a dial or a bill.
The fixed column does not move by a cent — 651.01 / 651.00 / 650.99 before and after — and the moving column rises to 177.03 / 116.92 / 79.05, taking the months to 828.04 / 767.92 / 730.04. The increases are 66.26, 47.34 and 28.40 in proportion to the 840 / 600 / 360 units. A hot summer is a moving-line event, and this page prices it exactly instead of splitting it by feel.
The monthly household bill page runs the bills as one monthly figure per room plus the yearly total. This page splits the same month into two classes first — fixed and moving — and answers a different question: what each room owes no matter what, what the month could still add, and which lines will and will not reopen next month. Both pages use the same arithmetic, so the room totals match between them.