What Is NOI? Net Operating Income for Real Estate Investors

Net Operating Income is the foundation of nearly every real estate investment metric. Before you can calculate cap rate, DSCR, or even monthly cash flow, you need to know your NOI. Here's exactly how it works.

What Is NOI?

Net Operating Income (NOI) is the annual income a property generates after subtracting all operating expenses — but before accounting for mortgage payments, capital expenditures, and income taxes. It represents the property's earning power independent of how it's financed.

Think of NOI as the property's "operating profit." It tells you how much money the property produces from its operations alone, without the noise of financing decisions.

The NOI Formula

More precisely:

Where Effective Gross Income = Gross Potential Rent - Vacancy & Credit Losses + Other Income (laundry, parking, pet fees, etc.)

What to Include (and Not Include)

Include in Operating Expenses

• Property taxes — your single largest expense in most markets
• Insurance — property, liability, and landlord coverage
• Property management fees — typically 8-10% of collected rent
• Maintenance & repairs — routine fixes, appliance repairs, landscaping
• Vacancy allowance — typically 5-8% of gross rent
• HOA fees — if applicable
• Utilities paid by owner — water, sewer, trash, common area electric
• Advertising & leasing costs — listing fees, tenant placement

Do NOT Include

• Mortgage payments — NOI is pre-debt
• Capital expenditures — roof replacement, HVAC, major renovations
• Depreciation — a tax concept, not an operating expense
• Income taxes — varies by investor, not by property
• One-time costs — closing costs, initial renovation

Worked Example

A $425,000 Duplex

Income:

• Unit A rent: $1,800/mo
• Unit B rent: $1,600/mo
• Gross potential rent: $3,400 x 12 = $40,800/year
• Vacancy (5%): -$2,040
• Effective gross income: $38,760

Operating Expenses:

• Property taxes: $5,100
• Insurance: $2,200
• Property management (8%): $3,101
• Maintenance (5%): $1,938
• Water/sewer/trash: $1,800
• Total: $14,139

NOI:

Why NOI Matters

NOI is the building block for the most important investment metrics:

• Cap Rate = NOI / Purchase Price
• DSCR = NOI / Annual Debt Service
• Property Valuation = NOI / Market Cap Rate (income approach)
• Monthly Cash Flow = (NOI / 12) - Monthly Mortgage Payment

If your NOI is wrong, every metric built on top of it is wrong. This is why experienced investors spend most of their analysis time verifying income and expense assumptions.

Common NOI Mistakes

1. Using the seller's NOI without verification — Sellers often understate expenses or overstate income. Always rebuild NOI from scratch.
2. Forgetting vacancy — Even in hot markets, budget 5% minimum for vacancy, turnover, and credit losses.
3. Not including management — Even if you self-manage, your time has value. Include 8-10% so you can compare properties apples-to-apples.
4. Confusing NOI with cash flow — NOI doesn't include mortgage payments. A property can have positive NOI but negative cash flow.
5. Including CapEx in NOI — Capital expenditures are below the NOI line. Including them inflates expenses and understates the property's operating performance.

NOI vs. Cash Flow

The key difference: NOI ignores financing, cash flow includes it.

• NOI = Rental income - Operating expenses
• Cash Flow = NOI - Mortgage payments - CapEx reserves

NOI is the same regardless of whether you pay cash or use a mortgage. Cash flow changes based on your loan terms. That's why NOI is used for property-level comparisons, while cash-on-cash return (which uses cash flow) is used for evaluating your personal return.

For a complete walkthrough of how all these metrics work together, see our 5-step rental property analysis guide.