Net Operating Income (NOI): Formula and What It Tells Investors

What Is Net Operating Income?

Net Operating Income (NOI) is the annual income a property generates after subtracting all operating expenses — but before paying the mortgage. It measures how the property performs on its own, independent of how it’s financed.

The formula:

NOI = Gross Revenue – Operating Expenses

NOI strips out the owner’s personal financial situation — their mortgage, their tax bracket, their depreciation schedule — and shows the raw earning power of the building. That’s why banks, appraisers, and investors all use it as the starting point for valuation.

When someone says a building “has $100,000 in NOI,” it means the property throws off $100,000 per year after all costs of operation, before debt service. From there, you can calculate the cap rate, determine market value, and figure out whether the property covers its mortgage with room to spare.

NOI is the foundation of commercial real estate valuation. Get it right and every other metric falls into place. Get it wrong — by miscounting expenses or inflating income — and your cap rate, cash-on-cash return, and offer price are all off.

NOI Formula Step-by-Step

The formula looks simple on paper. The detail is in getting each input right.

Start with Gross Potential Income (GPI)

Gross Potential Income is total rental income assuming every unit is occupied and every tenant pays on time. If you have a 12-unit building where each unit rents for $1,200/month:

$1,200 x 12 units x 12 months = $172,800 GPI

Add Other Income

Rental income isn’t the only revenue source. Other income streams include:

• Laundry machines: $200-$400/month for a 12-unit building
• Parking fees: $50-$150/space/month
• Storage rentals: $25-$75/unit/month
• Pet rent: $25-$50/pet/month
• Late fees and application fees: variable
• Vending machines: small but consistent

For our 12-unit building, other income totals $4,800/year (laundry $3,600, late fees $1,200).

Gross Potential Income + Other Income = $172,800 + $4,800 = $177,600

Subtract Vacancy and Collection Loss

No building runs at 100% occupancy with perfect collection every month. Vacancy and collection loss accounts for empty units and unpaid rent. Standard estimates range from 5% to 10%, depending on market and property quality.

For a well-managed B-class property in a solid market, budget 6% vacancy.

$177,600 x 0.06 = $10,656 vacancy loss

Effective Gross Income = $177,600 – $10,656 = $166,944

Subtract Operating Expenses

Operating expenses are the recurring costs of running the building. Subtract them from effective gross income to get NOI.

Effective Gross Income – Operating Expenses = NOI

The next section breaks down exactly what counts (and what doesn’t) as an operating expense.

What Counts as Operating Expenses

This is where most mistakes happen. Operating expenses include the costs of running the building day-to-day. They do NOT include costs related to your financing, taxes, or capital improvements.

Included in Operating Expenses

• Property taxes: Often the largest single expense. Check the county assessor’s site for current tax bills — don’t rely on the seller’s number, which may reflect a lower assessed value before sale.
• Property insurance: Landlord/commercial policy, liability coverage, and any umbrella policies.
• Maintenance and repairs: Routine upkeep like plumbing fixes, HVAC servicing, appliance repairs, painting, and general maintenance. Budget 8%-12% of gross rent for older properties.
• Property management: Whether you self-manage or hire a company. Third-party management runs 8%-10% of collected rent. If you self-manage, some investors still include 8% to reflect what it would cost — this gives a more accurate picture of the property’s standalone economics.
• Utilities (owner-paid): Water, sewer, trash, electric for common areas, gas for common boilers. If tenants pay their own utilities, this drops significantly.
• Landscaping and snow removal: Varies by region and property type.
• Administrative costs: Legal fees, accounting, advertising for vacancies, tenant screening.

NOT Included in Operating Expenses

• Mortgage payments (principal and interest): Debt service is the owner’s choice, not a property expense. NOI measures the building, not the owner’s loan.
• Depreciation: A tax deduction, not a cash expense.
• Income taxes: The owner’s tax situation, not the property’s.
• Capital expenditures (CapEx): New roof, parking lot repaving, boiler replacement — these are improvements, not operating expenses. Some investors set aside a CapEx reserve (3%-5% of income) but it’s technically not part of NOI.
• Tenant improvements (TI): Costs to prepare a unit for a new tenant (in commercial leases). These are a form of CapEx.

The distinction matters. Including mortgage payments in NOI — a common beginner error — gives you cash flow, not NOI. They’re different numbers used for different purposes.

Example NOI Calculation: 12-Unit Apartment

Full walkthrough for a 12-unit apartment building in a Midwest market.

NOI = $166,944 – $71,556 = $95,388

That $95,388 is the property’s annual earning power before debt service. Operating expenses represent about 43% of effective gross income — within the normal 40%-50% range for apartment buildings.

If this building is priced at $1,300,000, the cap rate is $95,388 / $1,300,000 = 7.34%. In a market where similar buildings trade at 7%-8%, this is fairly priced.

How Investors Use NOI

NOI isn’t just a number to calculate and file away. It’s the core input for three critical investor decisions.

Calculating Cap Rate

Cap Rate = NOI / Property Value

This tells you the unlevered yield. Our 12-unit building at $1,300,000 with $95,388 NOI produces a 7.34% cap rate. Compare that to similar buildings in the market to determine if the asking price is fair.

Valuing a Property

Property Value = NOI / Cap Rate

This is the income approach to valuation — and it’s how commercial real estate is priced. If the market cap rate for 12-unit apartments in this area is 7.5%, this building’s value is $95,388 / 0.075 = $1,271,840.

This creates a direct link between income improvement and property value. Increase NOI by $10,000 in a 7% cap rate market and the property’s value increases by $10,000 / 0.07 = $142,857. That’s the magic of forced appreciation: a $10,000 income improvement creates $143,000 in value.

Calculating Debt Service Coverage Ratio (DSCR)

DSCR = NOI / Annual Debt Service

Banks require a minimum DSCR (usually 1.20-1.25) to approve a commercial loan. If annual debt service on this building is $72,000, the DSCR is $95,388 / $72,000 = 1.32. The property produces 32% more income than needed to cover the mortgage — comfortable for the lender.

If NOI drops to $80,000 (a bad year), DSCR falls to 1.11 — below most lender thresholds. That’s when problems start. This is why lenders scrutinize NOI so carefully and why inflating it to get a loan approved backfires when reality doesn’t match projections.

NOI vs. Cash Flow vs. Net Income

Three related but different numbers. Here’s how they stack up.

Using the 12-unit example:

NOI shows $95,388 — strong. Cash flow after the mortgage is $23,388 — healthy but much lower. After-tax net income depends on the individual investor’s situation. Each metric tells a different story, and you need all three for a complete understanding.

How to Increase NOI

Since property value is directly tied to NOI (Value = NOI / Cap Rate), every dollar of NOI improvement creates a multiple of that dollar in property value. Here are concrete tactics.

Raise Rents to Market Rate

The simplest NOI improvement: if your rents are below market, raise them. Even a modest $50/month increase across 12 units adds $7,200/year to NOI. At a 7% cap rate, that’s $102,857 in added property value.

Check market rents using Zillow, Apartments.com, and local classifieds. If your units rent for $1,200 and comparable units lease for $1,350, you’re leaving $21,600/year on the table. Read more about setting the right rent price.

Add Ancillary Income Streams

• Coin-operated laundry: $3,000-$6,000/year revenue for a 12-unit building
• Covered parking or garages: $50-$150/space/month
• Storage units: Convert unused basement or garage space into rentable storage
• Pet rent: $25-$50/month per pet, plus one-time pet deposit
• Cable/internet bulk deal: Negotiate a building-wide contract and bill back to tenants at a small markup

Each stream may seem small, but combined they can add $10,000-$20,000/year to NOI.

Implement RUBS (Ratio Utility Billing System)

RUBS allocates water, sewer, and trash costs to tenants based on unit size or occupancy. If you’re paying $10,800/year in water/sewer/trash, shifting 70%-80% to tenants via RUBS reduces your operating expenses by $7,500-$8,600/year. That’s a direct NOI increase.

RUBS is legal in most states but check local regulations. It’s one of the most impactful NOI improvements available because it reduces expenses without requiring capital investment.

Reduce Vacancy

Dropping vacancy from 8% to 4% on $172,800 in gross rent saves $6,912/year. Ways to reduce vacancy: faster unit turns (target under 7 days), better tenant screening to reduce evictions, competitive pricing, and responsive maintenance that keeps good tenants in place.

Cut Operating Expenses

• Shop insurance annually: Rates vary widely between carriers. Get 3-4 quotes every renewal.
• Appeal property taxes: If the assessed value is higher than market value, file an appeal. Success rates are surprisingly high — around 40%-60% nationally.
• Negotiate service contracts: Landscaping, snow removal, pest control, and trash hauling are all negotiable.
• Energy efficiency: LED lighting in common areas, low-flow fixtures, smart thermostats — small investments with ongoing savings.

Each expense reduction drops straight to NOI. A 5% cut in operating expenses on a building running $71,556 in annual expenses saves $3,578 — worth over $51,000 in property value at a 7% cap rate.

For tools to manage this process, see our review of property management software. And for the broader framework of building wealth through rental properties, the beginner’s guide to real estate investing covers the full picture.

Frequently Asked Questions

What’s the difference between NOI and EBITDA?

They’re similar concepts in different contexts. EBITDA (Earnings Before Interest, Taxes, Depreciation, and Amortization) is used for businesses and corporate finance. NOI is the real estate equivalent — income before debt, taxes, and non-cash charges. For a property that’s purely a rental (no business operations beyond leasing), NOI and EBITDA are nearly identical. For properties with active businesses (hotels, self-storage, senior living), EBITDA is the more appropriate measure because it captures operational complexity beyond simple rent collection.

Can I calculate NOI for a single-family rental?

Absolutely. The math is the same — gross rent minus vacancy estimate minus operating expenses. The NOI on a single-family rental is just smaller in scale. Where it’s less commonly used: single-family homes are typically valued by comparable sales, not by income (cap rate). But calculating NOI still helps you understand the property’s cash flow potential and compare it to other rental property investments.

What’s a normal operating expense ratio?

Operating expenses typically run 35%-50% of effective gross income, depending on property type and age. Newer buildings with tenant-paid utilities might hit 35%. Older buildings with owner-paid water and high maintenance could reach 50% or more. If a seller presents an expense ratio below 30%, be skeptical — they’re likely excluding real costs. The gross rent multiplier gives you a quick way to cross-check whether reported numbers make sense.

What’s the difference between pro forma and actual NOI?

Actual NOI (also called “trailing” or “historical” NOI) uses real numbers from the past 12 months. Pro forma NOI is a projection — what the seller or broker thinks the property could produce under ideal conditions (higher rents, lower vacancy, reduced expenses). Always underwrite based on actual NOI. Pro forma numbers are sales tools, not investment tools. If the deal only works on pro forma, it doesn’t work.

If CapEx isn’t in NOI, how do I account for it?

Most investors calculate a CapEx reserve — typically 3%-5% of gross income — and subtract it from NOI when calculating true cash flow. A 12-unit building generating $172,800 in gross income should reserve $5,184-$8,640/year for eventual roof replacements, HVAC systems, parking lot work, and other major items. This isn’t technically part of NOI, but ignoring it means you’ll be blindsided when a $25,000 roof bill arrives. Smart investors keep the reserve in a separate account — the money is spoken for, even if it hasn’t been spent yet. For a deeper look at how NOI connects to your returns, pair this with the cap rate guide and cash-on-cash return calculator. Together, those three metrics — NOI, cap rate, and CoC — form the foundation of any rental property analysis. For city-level data on where these numbers look strongest, check the best cities to invest breakdown.