Noi

What it is

NOI is Net Operating Income. Gross rent collected in a year minus every operating expense, calculated before mortgage debt service.

NOI = Gross Rent - Vacancy - Operating Expenses

Operating expenses include property taxes, insurance, property management fees, maintenance, repairs, CapEx reserves, utilities the landlord covers, HOA, and any other cost to keep the building running. What it does NOT include: mortgage principal, mortgage interest, depreciation, or income taxes. Those sit outside the operating line.

NOI is the output of a property, not of a property owner. Two identical houses on the same street will have different cash flows depending on whether one carries a 12% hard money note and the other carries a 5% conventional loan. They have the same NOI.

Quick example: a house rented at $1,800/month, gross $21,600/year. Operating expenses: $2,400 taxes, $900 insurance, $1,700 management at 8%, $1,700 maintenance, $1,700 CapEx, $1,500 vacancy. That’s $9,900 in operating expenses. NOI is $11,700 per year, or $975 per month. If the mortgage at $150,000 at 7% for 30 years is about $998/month in P&I, you’re $23/month underwater before a single repair goes sideways. The gross number felt good. The NOI told the truth.

Why it matters

For single-family rentals, most investors look at cash flow. NOI sits one step above cash flow and is less forgiving. It exposes what the property actually earns on its own, independent of your financing.

For multi-family and commercial, this is the underwriting number. The income approach: NOI divided by cap rate equals property value. Change the NOI by $10,000 per year and the property’s value swings by $100,000 to $200,000, depending on the cap rate. Every dollar of avoidable operating expense is leaking future resale value, not just monthly cash flow. That’s why you tighten operating costs on multi-family — it’s not just about monthly income, it’s about building value.

For the Solo House Flipper, NOI is the honest mirror. It forces you to include the line items most new investors quietly skip. The 31 percent rule is a shortcut for this: 31% of gross rent gets eaten by vacancy, maintenance, CapEx, and property management before you ever touch the mortgage. On a $300,000 house renting for around $1,800/month, that’s roughly $558/month in operating costs before debt service. Whatever’s left is your NOI, and whatever survives the mortgage payment after that is your actual cash flow.

If your NOI doesn’t cover the mortgage with a comfortable cushion, the rental is speculation. Appreciation might bail you out. One bad tenant definitely won’t.

How it shows up

On my cash flow calculator, NOI is right there. Quick note from when I built it: NOI doesn’t include principal and interest. That’s everything else — vacancy, maintenance, CapEx, management — leaving the mortgage out of the picture. The tool shows you loan amount, P&I, taxes, insurance, and then NOI separately, so you can see exactly what the property earns before the bank takes its cut.

For rentals you’re analyzing: always include management fees even if you’re self-managing. Run the numbers as if you were paying someone 8-10% to manage it. The day you decide you’re too busy to manage it yourself, you need to know the deal still works.

Related

cap rate, 31 percent rule, cash flow, 1 percent rule, capex, wealth engines