You own five rental properties across two LLCs. Three are Section 8, two are conventional. One just had a new HVAC installed, and another has been vacant for six weeks.
Quick: which property is actually making you money?
If you had to open a spreadsheet, pull up three PM statements, and do math on the back of an envelope to answer that question, you have an NOI problem. And you’re not alone.
Net Operating Income is the single most important number for understanding whether a rental property is performing or bleeding. It strips away financing, depreciation, and capital expenditures to show you exactly how much a property earns on its own. Yet most landlords with property managers either calculate it wrong, calculate it once a year at tax time, or never calculate it at all.
Here’s how to fix that.
What NOI Actually Measures
NOI tells you how much income a property generates after paying all the costs required to operate it. That’s it. No mortgage payments, no depreciation, no capital improvements. Just revenue minus the day to day cost of keeping the property running.
The formula:
NOI = Gross Rental Income + Other Income - Operating Expenses
Three components. Sounds simple. The complexity is in knowing what goes into each bucket.
Breaking Down the Three Components
Gross Rental Income
This is the total rent collected (not just what’s owed). If your lease says $1,200/month but your tenant paid $1,000 last month and owes you $200, your gross rental income for that month is $1,000.
For Section 8 landlords, this includes both the tenant portion and the Housing Assistance Payment (HAP) from the housing authority. If your contract rent is $1,100 and the HAP covers $950 while the tenant pays $150, your gross rental income is $1,100 when both pay on time.
Important: use actual collected rent, not pro forma or projected rent. NOI based on what you wish you collected is fiction.
Other Income
Most single family rental investors skip this line because they think it doesn’t apply to them. But other income includes late fees actually collected, lease application fees, pet rent or pet deposits (non refundable), utility reimbursements, and any other income tied to operating the property.
For a typical single family rental, this might be $0 to $50/month. For a small multifamily, it could include laundry income, parking fees, or storage rentals.
Operating Expenses
This is where most landlords get it wrong. Operating expenses include everything it costs to keep the property running, but not everything you spend on it.
Include in operating expenses:
Property management fees (typically 8% to 10% of collected rent), property taxes, property insurance, routine repairs and maintenance (leaky faucet, broken outlet, lawn care), utilities you pay as the landlord (water, sewer, trash in some markets), vacancy costs (marketing, turnover cleaning, make ready costs), HOA fees if applicable, pest control, and licensing or inspection fees.
Do NOT include in operating expenses:
Mortgage payments (principal and interest), capital expenditures (new roof, HVAC replacement, full rehab), depreciation, income taxes, and loan origination fees or closing costs.
The most common mistake is lumping a $7,000 HVAC replacement into operating expenses. That’s a capital expenditure. It improves the property beyond its current condition. Including it in your NOI calculation makes the property look like it’s losing money when it’s actually performing fine operationally.
A Real Example: Property by Property
Let me walk through a three property portfolio to show how this works in practice.
Property A: Section 8 SFR in Birmingham, AL
Monthly collected rent: $1,100 (HAP $950 + tenant $150)
Other income: $25/month (pet rent)
Monthly operating expenses: PM fee $110, insurance $95, taxes $75, repairs $60, pest control $15, water/sewer $45
Total monthly expenses: $400
Monthly NOI: $1,100 + $25 - $400 = $725
Annual NOI: $8,700
Property B: Conventional SFR in Birmingham, AL
Monthly collected rent: $1,050
Other income: $0
Monthly operating expenses: PM fee $105, insurance $100, taxes $80, repairs $85, lawn care $50
Total monthly expenses: $420
Monthly NOI: $1,050 + $0 - $420 = $630
Annual NOI: $7,560
Property C: Section 8 SFR in Birmingham, AL (had 6 weeks vacancy)
Monthly collected rent (annualized): $1,000/month x 10.5 months = $10,500 annual
Other income: $0
Annual operating expenses: PM fee $1,050, insurance $1,080, taxes $900, repairs $1,200, turnover costs $800, vacancy marketing $150
Total annual expenses: $5,180
Annual NOI: $10,500 + $0 - $5,180 = $5,320
Monthly NOI (effective): $443
Now you can see it clearly. Property A is your best performer at $725/month NOI. Property C looks decent on paper ($1,000 rent) but the vacancy and turnover costs drag it down to $443/month effective NOI. That’s a 39% difference that’s invisible if you only look at rent amounts.
Why Calculating NOI Per Property Matters
When you have multiple properties, portfolio level numbers hide the truth. A portfolio NOI of $1,798/month across three properties sounds fine. But knowing that Property C is underperforming by nearly $300/month compared to Property A tells you where to focus.
Specifically, per property NOI helps you answer these questions:
Should I keep or sell this property? If a property’s NOI has been declining for 12+ months and there’s no obvious fix (like a needed rent increase or PM change), it might be time to 1031 exchange into something better.
Is my property manager doing a good job? Compare NOI trends across properties managed by the same PM. If one property’s NOI keeps dropping while others are stable, dig into the expenses. Are repair costs unusually high? Is vacancy lasting longer than market average?
Am I charging enough rent? If your NOI margin (NOI divided by gross income) is below 50% on a single family rental, your expenses might be normal but your rent might be below market.
Which property should I refinance first? Lenders care about NOI because it determines the debt service coverage ratio (DSCR). A property with strong, consistent NOI is a better refinance candidate than one with volatile income.
The NOI Margin: Your Efficiency Score
Beyond the raw NOI number, track your NOI margin for each property:
NOI Margin = NOI / Gross Operating Income x 100
Using the examples above:
Property A: $725 / $1,125 = 64.4% margin
Property B: $630 / $1,050 = 60.0% margin
Property C: $443 / $875 (effective monthly) = 50.6% margin
For single family rentals with property managers, a healthy NOI margin is typically 55% to 65%. Below 50% means your expenses are eating too much of your income. Above 65% is excellent and might mean you’re deferring maintenance (which catches up to you eventually).
How to Track NOI Without Losing Your Mind
Calculating NOI once is straightforward. Calculating it every month across 5, 10, or 20 properties while your PM sends you statements in different formats, your insurance renews at random times, and tax bills come quarterly? That’s where landlords give up and go back to guessing.
The key is automation. Every transaction that hits your property needs to be categorized correctly: is it operating income, other income, an operating expense, or a capital expenditure? Get that categorization right, and your NOI calculates itself.
This is exactly what DoorVault’s Knox AI does. When you forward your PM statement, Knox reads it, extracts every line item, categorizes each transaction, and updates your per property P&L automatically. Your NOI is always current, always accurate, and always broken down by property.
No spreadsheet. No manual data entry. No wondering if that $800 charge was a repair or a capital improvement.
Start Tracking Today
If you’re not calculating NOI per property right now, here’s your action plan:
- List every property you own
- Pull the last 12 months of PM statements for each
- Separate operating expenses from capital expenditures
- Calculate annual NOI and NOI margin for each property
- Rank your properties from best to worst performer
- Ask yourself: does anything need to change?
Or skip steps 2 through 5 entirely.
See how Knox calculates your per property NOI automatically. Try the live demo
