What Is Net Operating Income (NOI)?
Net operating income measures the cash a property generates from its operations before financing and ownership-level costs. It starts with all property revenue, primarily rent plus ancillary income like parking or laundry fees, and subtracts the expenses required to run the building. Because it stops before debt service, NOI describes the earning power of the asset itself rather than the fortunes of any particular owner.
That independence from capital structure is what makes NOI so useful. Two investors might buy the same building with completely different mortgages, yet the property's NOI would be identical in both hands. In that sense, NOI plays the same role in real estate that EBITDA plays in corporate finance: a capital-structure-neutral yardstick for comparing assets.
How to Calculate NOI
The formula is NOI = effective gross income - operating expenses. Effective gross income equals potential rental income at full occupancy, minus an allowance for vacancy and credit losses, plus other income streams. Operating expenses include items such as property taxes, insurance, utilities, repairs and maintenance, and property management fees. Excluded from the calculation are mortgage payments, income taxes, depreciation, and capital expenditures like a roof replacement.
Consider an apartment building with $2.5 million of potential rent, a 5% vacancy allowance, and $100,000 of other income, producing effective gross income of $2,475,000. If operating expenses run $975,000, NOI is $1.5 million. At a 6% market cap rate, that NOI supports a valuation of $25 million, which shows how directly the metric feeds into pricing.
Why NOI Matters
NOI drives both valuation and financing. Appraisers capitalize NOI to estimate value, and lenders size loans off it through the debt service coverage ratio, which compares NOI to required loan payments. A lender requiring 1.25x coverage on a property with $1.5 million of NOI will cap annual debt service at $1.2 million, effectively setting the maximum mortgage the asset can carry.
Because small NOI changes translate into large value changes at prevailing cap rates, operators focus intensely on growing it, whether by raising rents, filling vacant space, or cutting controllable expenses. Analysts should also watch for manipulation: sellers sometimes present NOI with understated expense assumptions or classify recurring maintenance as capital spending to flatter the number, which is why buyers rebuild NOI from source documents during due diligence.
