NOI Explained: The Number Every Landlord Should Know

Net operating income is one of those terms landlords hear constantly and often calculate slightly wrong — usually by including something that shouldn't be there, like mortgage payments or capital expenditures.

The formula

NOI = Gross Rental Income − Operating Expenses. Operating expenses include property taxes, insurance, maintenance, property management fees, and utilities the landlord pays — but explicitly excludes mortgage principal and interest, and capital improvements.

Why mortgage payments are excluded

NOI is meant to measure how a property performs independent of how it's financed, so two identical properties — one bought with cash, one heavily mortgaged — should show the same NOI even though their actual cash flow differs significantly.

What NOI is used for

NOI is the input for several other key metrics, most notably cap rate (NOI ÷ property value) and debt service coverage ratio, which lenders use to evaluate whether a property generates enough income to comfortably cover its mortgage.

A common mistake in calculating it

Landlords sometimes include vacancy loss inconsistently, or forget to account for it at all, resulting in an inflated NOI that doesn't reflect real-world performance. A realistic vacancy assumption should be subtracted from gross potential rent before calculating NOI.