Net operating income (NOI) is the property's total income minus all operating expenses, before accounting for debt service, income taxes, depreciation, or capital expenditures. Operating expenses include property taxes, insurance, property management fees, maintenance, utilities (if owner-paid), and vacancy allowance. NOI is the foundation for calculating cap rate, DSCR, and property valuations. Investors should scrutinize the expense assumptions in any pro forma, as understated expenses can make a deal look far better than reality. A thorough NOI analysis is the starting point for any serious investment evaluation.