How to Calculate Net Operating Income in Real Estate

To calculate net operating income in real estate, take the rent and other income a property actually collects in a year and subtract its recurring operating expenses. The result, NOI, measures how the building itself performs before any mortgage payment, income tax, or capital project enters the picture. That deliberate omission is what makes the number useful: it lets you compare two properties on equal footing regardless of who owns them or how they’re financed.¹

The Formula

Net Operating Income = Effective Gross Income − Operating Expenses

Effective Gross Income is what the property actually collects after vacancies and unpaid rent, plus any non-rent revenue. Operating expenses are the recurring costs of running the building. Everything else — loan payments, depreciation, income taxes, big one-time projects — stays out.¹

Building the Income Side

Gross Potential Income

Start with Gross Potential Income: the total rent the property would generate if every unit were leased at current market rates for the full year. Pull it from the rent roll. A 20-unit building at $1,500 per unit per month produces a GPI of $360,000.

Vacancy and Credit Loss

No property stays fully occupied with every tenant paying in full. The vacancy and credit loss adjustment reflects the income lost when units sit empty between tenants or when a renter stops paying. A well-located multifamily property typically falls in the 5% to 7% range, and softer markets or properties with high turnover run higher. Look at the last two to three years of actual vacancy and compare it against the submarket average. Cross-reference the rent roll against bank deposits to confirm what was actually collected versus what was billed.

Other Income

Most income properties earn revenue beyond base rent. Parking fees, storage rentals, laundry, pet fees, and late charges all count, and on a larger multifamily property they can add 3% to 5% to the revenue total. Skipping them understates the building’s earning power.¹

Effective Gross Income

Take GPI, subtract vacancy and credit loss, then add other income. That’s Effective Gross Income — the cash the property actually brings in during a typical year.

Operating Expenses That Count

Operating expenses are the recurring costs required to keep the property functional and generating income. If a cost shows up every year as part of normal operations, it belongs. The standard categories:

Property taxes, often the single largest line. Use the actual bill, not an estimate.
Insurance premiums for property damage, liability, and any umbrella coverage.
Repairs and maintenance: landscaping, plumbing fixes, appliance repairs, seasonal work like snow removal.
Utilities for common areas the owner pays. If tenants pay their own directly, only the owner-paid portion counts.
Property management fees, generally 4% to 12% of gross rental income depending on property type, size, and location. Include this even if you self-manage, because it reflects the market cost of running the building and keeps the NOI comparable to professionally managed properties.
Legal and professional fees tied to day-to-day operations, such as lease preparation or evictions.¹
Advertising and leasing costs to market vacant units.

Base every line item on actual historical spending verified against bank statements and invoices, not projections. A seller’s pro forma expenses tend to be optimistically low. Underwriting from real financials protects you against overpaying for a building whose costs are higher than advertised.

What Stays Out of NOI

Certain costs are intentionally excluded, and knowing which ones prevents a common category of error.

Debt Service

Mortgage principal and interest are the biggest omission. Two owners can buy the same building with different down payments, rates, and terms. Including debt service would produce two different NOI figures for the same building generating the same income, which defeats the metric.²

Depreciation

Depreciation is a tax deduction that lets owners recover the cost of a building over time. It reduces taxable income but no check gets written. The IRS sets the recovery period at 27.5 years for residential rental property and 39 years for commercial real property under the Modified Accelerated Cost Recovery System.³⁴ Because it’s a non-cash entry, it stays out.

Income Taxes

A property’s contribution to your tax bill depends on your overall financial picture, not the building. Two owners of identical properties can face very different tax burdens. Keeping income taxes out of NOI keeps the number about the property.

Capital Expenditures

Large, infrequent improvements — a new roof, a full HVAC replacement, repaving the parking lot — are capital expenditures, not operating expenses. They extend the useful life of the asset and get depreciated over multiple years. Including them would distort steady-state performance: a year with a $150,000 roof replacement would look catastrophically unprofitable next to a normal year even though nothing about operations had changed.¹

Replacement Reserves

Reasonable people disagree here. Replacement reserves are annual set-asides earmarked for future capital projects. The conventional investor approach excludes them, producing a higher NOI. Lenders often include them as an operating expense, which lowers NOI and yields a more conservative valuation. If you’re preparing NOI for a loan application, expect the lender to deduct reserves. If you’re evaluating for yourself, know that excluding them makes the property look more profitable than it will feel when the boiler dies. Run it both ways and know which version you’re looking at.

A Worked Example

A 30-unit apartment building rents each unit at $1,200 per month. The income side:

Gross Potential Income: 30 × $1,200 × 12 = $432,000
Vacancy and credit loss at 6%: −$25,920
Other income (parking, laundry): +$18,000
Effective Gross Income: $424,080

Annual operating expenses:

Property taxes: $48,000
Insurance: $14,000
Repairs and maintenance: $28,000
Utilities (common areas): $12,000
Property management at 8%: $33,926
Legal and professional fees: $4,000
Advertising: $2,500
Total operating expenses: $142,426

Net Operating Income: $424,080 − $142,426 = $281,654

That $281,654 is what the building earns from operations before any mortgage payment, tax liability, or capital project. Financing the purchase will reduce your actual cash flow below that figure; paying all cash will leave you with roughly that amount minus income taxes.

Mistakes That Throw the Number Off

The formula is simple. The errors happen in the inputs. Using a seller’s projected rents instead of actual lease rates inflates GPI. Applying a 3% vacancy assumption in a market running 8% understates losses. Omitting management fees because the current owner self-manages makes the building look cheaper to operate than it would for a buyer who hires a manager. Each of these distortions flows directly into anything you calculate from NOI, compounding the error where it matters most.

The other common trap is confusing NOI with profit. A building showing $300,000 in NOI might produce $40,000 in actual cash flow after debt service and reserves, or the full $300,000 if the owner paid all cash. NOI is a standardized performance metric for the building. Whether the deal works for you depends on your financing, your tax situation, and how much capital the property will need during your hold.

Why the Number Matters

Valuation

NOI drives property value through the capitalization rate. Divide NOI by purchase price to find a cap rate, or divide NOI by the prevailing market cap rate to estimate value. This is how appraisers apply the income capitalization approach. Every dollar of NOI added, or operating expense reduced, has a multiplied effect on appraised value: at a 6% cap rate, an extra $10,000 in annual NOI increases value by roughly $167,000.⁵²

Loan Qualification

Lenders divide NOI by annual debt service to get the Debt Service Coverage Ratio. A DSCR of 1.0 means the property earns exactly its loan payments. Most institutional lenders require at least 1.20 to 1.25 on standard commercial loans, meaning the property must generate 20% to 25% more income than the mortgage costs.⁶ An overstated NOI can make a deal look financeable when it isn’t, which is why getting the inputs right at the NOI stage carries all the way through underwriting.

1
J.P. Morgan. Calculating Net Operating Income in Multifamily Real Estate
2
PNC Insights. Capitalization Rate: What It Is and How Its Calculated
3
Internal Revenue Service. Publication 527 (2025), Residential Rental Property
4
Internal Revenue Service. Publication 946 (2025), How To Depreciate Property
5
JPMorgan Chase. The Role of Cap Rates in Real Estate
6
J.P. Morgan. What Is Debt Service Coverage Ratio (DSCR) in Real Estate