How to Calculate NOI for a Rental Property (Step by Step)
NOI sounds like accounting jargon. It's actually the most useful number on a rental property: the cash that's left after the property pays its operating bills, but before the mortgage takes its cut. By the end of this article you'll be able to calculate NOI on any property in under 10 minutes with confidence, using a real $200,000 duplex example to walk through every step.
This article is for first-time investors who keep seeing "NOI" in deal listings and want to actually understand what it means. If you've been intimidated by the accounting-flavored term, you're not alone. We'll define it clearly, walk through what's included and excluded, and run the math on a real property.
Key Takeaways
- NOI formula: Annual Rental Income minus Operating Expenses (before mortgage).
- On our $200,000 duplex generating $24,816 in effective gross income with $9,252 in operating expenses, NOI is $15,564.
- Mortgage payments are NOT included because NOI measures the property's operating performance, not your financing.
- NOI is the foundation of cap rate (cap rate = NOI ÷ purchase price).
- The most common mistakes: ignoring vacancy reserves, ignoring capex, and skipping property management fees if you self-manage.
Table of contents
- The NOI formula (one line)
- What counts as effective gross income
- What counts as operating expenses
- Step-by-step: a real Indianapolis duplex
- NOI vs cashflow vs net income (the three confusing terms)
- NOI as the "salary" of the property
- Common NOI mistakes (and how to avoid them)
The NOI formula (one line)
NOI (net operating income) is the standard cashflow metric used in commercial real estate per Fannie Mae's underwriting standards and reported on Schedule E per IRS Publication 527.
NOI = Effective Gross Income - Operating Expenses
Where:
- Effective Gross Income = potential rent minus vacancy reserve plus other income (laundry, parking, etc.)
- Operating Expenses = everything the property costs to run, except the mortgage
That's it. The formula has two terms. The work is in calculating each one correctly.
What counts as effective gross income
Per Investopedia's NOI definition, effective gross income is what the property actually produces, not what it could produce in perfect conditions.
Build it in three steps:
1. Potential gross rental income = full rent if every unit is occupied 100% of the year.
- 2-unit duplex × $1,100/month × 12 months = $26,400/year
2. Vacancy reserve = subtract 5-8% to account for inevitable vacancies.
- $26,400 × 6% vacancy = $1,584 reserved
- $26,400 - $1,584 = $24,816
3. Other income = add any non-rent income (coin laundry, parking, storage, pet fees).
- For a typical duplex with no extras: $0
- Total: $24,816
If your property has unusual extras (a parking lot, billboard, cell tower lease), add those. For most residential rentals, other income is small or zero.
What counts as operating expenses
Operating expenses are the recurring costs of running the property. The standard categories:
Always include:
- Property taxes: from the county assessor (don't trust listing estimates)
- Insurance: get a real quote from your broker for the actual property
- Property management fees: 8-10% of gross rent, even if you self-manage
- Repairs and maintenance: 5-10% of gross rent (paint, fixtures, small fixes)
- Capital expenditure reserve: 5-10% of gross rent (saved for big-ticket items like roofs, HVAC)
- Utilities you pay: water, trash, sewer, sometimes lawn or snow removal
- HOA fees: if applicable
Sometimes include:
- Pest control, lawn service, snow removal: depends on lease structure (who pays?)
- Marketing and tenant screening: small but real
- Accounting and legal fees: for the property specifically
NEVER include:
- Mortgage principal and interest (covered separately in cashflow)
- Capital improvements (roof replacement, full renovation, additions)
- Depreciation (a tax/accounting concept, not a cash expense)
- Income taxes (your personal taxes, not the property's)
The mortgage exclusion is the biggest source of confusion for beginners. The reasoning: if NOI included the mortgage, the same property would have a different NOI for every buyer based on their down payment and interest rate. By excluding the mortgage, NOI lets you compare properties apples-to-apples regardless of how they're financed.
Step-by-step: a real Indianapolis duplex
Let's calculate NOI for a $200,000 duplex in Indianapolis with both sides renting at $1,100/month.
Step 1: Effective Gross Income
| Item | Amount |
|---|---|
| Both sides at $1,100/mo × 12 | $26,400 |
| Less 6% vacancy reserve | ($1,584) |
| Other income (laundry, etc.) | $0 |
| Effective Gross Income | $24,816 |
Step 2: Operating Expenses
| Expense | Annual amount | Notes |
|---|---|---|
| Property taxes | $2,100 | Indiana average ~1.05% on $200k |
| Insurance | $1,800 | Multifamily quote from local broker |
| Property management (8%) | $2,112 | Even if self-managing |
| Repairs and maintenance (5%) | $1,320 | Paint, fixtures, minor fixes |
| Capex reserve (5%) | $1,320 | For roofs, HVAC, water heaters |
| Lawn and snow service | $600 | Common for duplex landlord |
| Total Operating Expenses | $9,252 |
Step 3: Calculate NOI
NOI = $24,816 - $9,252 = $15,564
This duplex's NOI is $15,564 per year (or $1,297/month).
That's the number you'd plug into cap rate to compare this property to others. ($15,564 / $200,000 = 7.78% cap rate, in case you're keeping score.)
NOI vs cashflow vs net income (the three confusing terms)
Three numbers that sound similar but mean different things:
| Term | What it means | Includes mortgage? | Used for |
|---|---|---|---|
| NOI (Net Operating Income) | Income after operating expenses | No | Comparing properties, calculating cap rate |
| Cashflow | What's actually in your pocket each month | Yes (subtracted) | Personal budgeting, evaluating financed deals |
| Net Income | Accounting-level profit including depreciation | Yes (interest portion) | Tax filings (Schedule E) |
For our Indianapolis duplex with NOI of $15,564:
- NOI: $15,564/year ($1,297/month)
- Cashflow (assuming 6.5% mortgage on $160,000): $15,564 - $12,132 mortgage = $3,432/year ($286/month)
- Net Income (after depreciation of about $5,800/year per IRS Publication 527): roughly $0 on paper, depending on interest deduction
Same property. Three different numbers. Each useful for a different decision.
NOI as the "salary" of the property
Here's the analogy: NOI is the property's salary. Cashflow is what's left after the mortgage takes its bite.
When you take a job, your salary is what the company pays you. Your take-home is what's left after taxes and benefits get deducted. NOI is the property's salary; cashflow is the property's take-home pay.
This analogy holds for one important reason: salaries are comparable across companies, but take-home depends on each person's specific tax situation. NOI is comparable across properties; cashflow depends on each buyer's specific financing. That's why NOI is the foundation metric.
Common NOI mistakes (and how to avoid them)
Mistake 1: Skipping the vacancy reserve. Listings often show "potential gross income" with 100% occupancy. That's not realistic. Always subtract 5-8% before calling it gross income.
Mistake 2: Ignoring capex. Roofs cost $8,000-15,000. HVAC systems cost $5,000-10,000. If you don't reserve for these annually, your "NOI" looks great until the year you need a new roof. Then you're scrambling. Reserve 5-10% of gross rent every year.
Mistake 3: Self-managing without including the management fee. If you self-manage, you're trading your time for what a property manager would charge (8-10% of rent). The property's NOI shouldn't look better just because you're working for free. Include the fee in expenses; track your savings separately as your "labor income."
Mistake 4: Treating the mortgage as an operating expense. Don't. Calculate NOI first, then subtract the mortgage in a separate cashflow calculation. If you blend them, you can't compare your property to others.
Mistake 5: Using listing-quoted property taxes. Listings often show what the previous owner paid. After purchase, your property is reassessed, often at the new sale price. Pull current tax info from the county assessor's website before assuming.
Frequently Asked Questions
Why doesn't NOI include the mortgage?
NOI measures the property's operating performance, not your specific financing structure. If NOI included your mortgage, the same property would have a different NOI for every buyer based on their down payment and interest rate. By excluding the mortgage, NOI lets investors compare properties apples-to-apples. Your mortgage shows up later in the cashflow calculation, not in NOI.
What's the difference between NOI and cashflow?
NOI is what's left after operating expenses but before the mortgage. Cashflow is what's left after the mortgage too. So if your NOI is $1,500/month and your mortgage P&I is $1,200/month, your cashflow is $300/month. NOI is about the property; cashflow is about your specific deal with that property.
Should I include capital improvements in operating expenses?
No, but the line is blurry. Routine maintenance (painting, fixing a faucet, replacing a screen door) goes in operating expenses. Major capital improvements that extend the property's life or increase its value (a new roof, full HVAC replacement, a new driveway) don't. They're tracked separately as capex. Including them in NOI would understate the property's true operating performance in normal years.
How do I handle vacancy when calculating NOI?
Subtract a vacancy reserve from your potential gross income before calculating expenses. If your potential rent is $24,000/year and you assume 6% vacancy, your effective gross income is $24,000 × (1 - 0.06) = $22,560. Then subtract operating expenses from that. This gives you a more honest NOI than assuming 100% occupancy. Most experienced investors use a 5-8% vacancy reserve.
Does property management cost go into NOI?
Yes. Whether you self-manage or hire a property manager, you should still include the management fee in NOI (typically 8-10% of rent). If you self-manage, you're trading your time for the fee a third party would charge; the property's NOI shouldn't look better just because you're working for free. Including the fee gives you a more accurate picture of what the property would produce in a hands-off scenario.
What's a good NOI for a rental property?
There's no single number; it depends on the purchase price. NOI by itself is meaningless. The useful metric is the ratio of NOI to purchase price (which is the cap rate). For most residential rentals in the U.S., a healthy NOI corresponds to a cap rate of 6-10%. So a $200,000 property should typically produce $12,000-$20,000 in NOI per year to be considered a good investment.
NOI is the building block for everything else: cap rate, valuation, sale price, refinance qualification. Get it right, and the rest of your deal analysis works. Get it wrong, and every downstream calculation is corrupted. The free PDF guide includes a one-page NOI calculator template. The 28-day course walks through deal analysis in week 4 with NOI built into every example.