Duplex profit and loss per unit: splitting shared costs and finding NOI
One bill, two tenants: a per-unit view needs a stated rule for who carries shared costs. This guide splits a shared water bill, builds the per-unit P&L, and ends at NOI for each unit.
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General information only, not tax, legal or accounting advice. Late-fee, deposit and notice rules vary by state, city and lease; check your own. Tax references describe US federal pages on irs.gov as of the date above.
Why a per-unit view
The 2025 Schedule E has a column per property (labeled A, B and C), not per unit. A per-unit profit and loss is therefore for your own decisions: which unit earns more, which one eats repairs, whether a rent increase is overdue. The form has no per-unit column to fill in.
Direct costs and shared costs
Add one column to your expense log: Unit, holding A, B or "Shared." A repair inside Unit B is tagged B. A water bill for the whole building, the property tax and the lawn service are tagged Shared. Direct costs go to their unit; shared costs get split by a rule you choose.
Splitting a shared bill
Take a $2,160 annual water bill for a two-unit building.
Equal (50/50): =Bill / 2 = 2,160 / 2 = 1,080 per unit
By unit count: =Bill / Units = 2,160 / 2 = 1,080 per unit
By square feet: =Bill x UnitSqFt / BuildingSqFt
Unit A 900 of 2,000 sq ft: 2,160 x 900 / 2,000 = 972
Unit B 1,100 of 2,000: 2,160 x 1,100 / 2,000 = 1,188
Check: 972 + 1,188 = 2,160In a duplex, an equal split and a split by unit count are the same thing. They diverge in a three-unit building ($2,160 / 3 = $720 each) or if you start counting only occupied units. A split by unit count ignores unit size and how many people live there; a split by square feet or occupants follows use more closely but needs more inputs. Pick one, write it on the sheet, and use it all year.
What the IRS says about dividing expenses
The IRS pages cited here cover dividing an expense between rental and personal use, not between two rented units. When you rent part of your property, Publication 527 (2025) says you can use any reasonable method to divide an expense, that it may be reasonable to divide water by the number of people using it, and that the two most common methods are the number of rooms and the square footage. Its duplex example has you living in one half and renting the other, with halves of about the same size: with $10,000 of mortgage interest and $2,000 of real estate taxes for the whole property, $5,000 and $1,000 go on Schedule E.
Worked example: annual P&L per unit
Unit A collected $17,400 (12 months at $1,450). Unit B collected $14,850 (11 months at $1,350, one month vacant). Repairs were tagged directly: $410 to A and $1,075 to B. Shared costs were water $2,160, property tax $4,200 and landscaping $600, each split in half.
| Unit A | Unit B | Building | |
|---|---|---|---|
| Rent collected | $17,400 | $14,850 | $32,250 |
| Repairs (direct) | $410 | $1,075 | $1,485 |
| Water (shared, split in half) | $1,080 | $1,080 | $2,160 |
| Property tax (shared, split in half) | $2,100 | $2,100 | $4,200 |
| Landscaping (shared, split in half) | $300 | $300 | $600 |
| Operating expenses | $3,890 | $4,555 | $8,445 |
| NOI | $13,510 | $10,295 | $23,805 |
Direct, Unit A =SUMIFS(ExpenseLog[Amount], ExpenseLog[Unit], "A") = 410
Shared total =SUMIFS(ExpenseLog[Amount], ExpenseLog[Unit], "Shared") = 2,160 + 4,200 + 600 = 6,960
Unit A expenses = 410 + 6,960 / 2 = 410 + 3,480 = 3,890
Unit B expenses = 1,075 + 3,480 = 4,555
Unit A NOI = 17,400 - 3,890 = 13,510
Unit B NOI = 14,850 - 4,555 = 10,295
Building check = 13,510 + 10,295 = 23,805 = 32,250 - 8,445Unit B earns $3,215 less NOI than Unit A: $2,550 less rent collected (a lower rent and one vacant month) plus $665 more in direct repairs. The shared costs, split equally, explain none of the gap, which is the point of splitting them by a fixed rule.
What NOI means here
In this guide, NOI is rent collected minus operating expenses, before mortgage payments, depreciation and income tax. It is a management figure, not a Schedule E line. On the form, line 20 total expenses also includes mortgage interest (line 12) and depreciation (line 18), which NOI leaves out.
What this does not cover
This is not tax advice. It does not work out the split when you live in one of the units, and it does not build a depreciation schedule. Separate utility meters, tenants who reimburse part of a shared bill, and state rules on what you may charge tenants all change the setup, so check them. The split rule is your judgment, so note it on the sheet.
Sources
More landlord guides
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Already built
The Landlord Rent & Expense Tracker's Expenses tab lets each cost be tagged to a unit or marked shared, and it splits shared costs by unit count with SUMIFS roll-ups. The P&L tab then shows profit per unit and per property by month, including NOI. One Excel file, $29 one-time, no bank link and no account.