Net Operating Income Calculator Formula

Understand the math behind the net operating income calculator. Each variable explained with a worked example.

Use the Net Operating Income Calculator

Formulas Used

Net Operating Income

noi = egi - total_expenses

Effective Gross Income

effective_gross = egi

Total Operating Expenses

total_operating_expenses = total_expenses

Operating Expense Ratio

expense_ratio = (total_expenses / egi) * 100

Variables

VariableDescriptionDefault
gross_rental_incomeGross Rental Income(USD)72000
other_incomeOther Income(USD)3600
vacancy_pctVacancy & Credit Loss(%)7
property_taxesProperty Taxes(USD)6000
insuranceInsurance(USD)2400
maintenanceRepairs & Maintenance(USD)4800
management_feeManagement Fees(USD)5040
other_expensesOther Expenses(USD)2400
gross_potentialDerived value= gross_rental_income + other_incomecalculated
vacancy_lossDerived value= gross_potential * vacancy_pct / 100calculated
egiDerived value= gross_potential - vacancy_losscalculated
total_expensesDerived value= property_taxes + insurance + maintenance + management_fee + other_expensescalculated

How It Works

Net Operating Income (NOI)

NOI is the most important metric in commercial real estate. It represents the income a property generates after all operating costs but before debt service and income taxes.

Formula

NOI = Effective Gross Income - Total Operating Expenses

Where:

  • Effective Gross Income = Gross Potential Income - Vacancy Loss
  • Operating Expenses include taxes, insurance, maintenance, management, utilities
  • Debt service (mortgage payments) is NOT included in operating expenses

    • Worked Example

    A rental property earns $72,000 gross rent plus $3,600 other income, with 7% vacancy and $20,640 total expenses.

    gross_rental_income = 72000other_income = 3600vacancy_pct = 7property_taxes = 6000insurance = 2400maintenance = 4800management_fee = 5040other_expenses = 2400
    1. 01Gross potential income: $72,000 + $3,600 = $75,600
    2. 02Vacancy loss: $75,600 x 7% = $5,292
    3. 03Effective gross income: $75,600 - $5,292 = $70,308
    4. 04Total expenses: $6,000 + $2,400 + $4,800 + $5,040 + $2,400 = $20,640
    5. 05NOI: $70,308 - $20,640 = $49,668
    6. 06Expense ratio: $20,640 / $70,308 = 29.4%

    When to Use This Formula

    • Evaluating the income-generating potential of a rental property independent of how it is financed, to compare properties on an equal basis.
    • Calculating the cap rate of a property by dividing NOI by the purchase price, which is the standard profitability metric in commercial real estate.
    • Preparing a pro forma for a property acquisition or refinancing that lenders and investors require to assess the deal.
    • Identifying which operating expenses are eating into profitability and where cost reductions would have the greatest impact on the bottom line.
    • Tracking property performance year over year to see whether income growth is outpacing expense growth.

    Common Mistakes to Avoid

    • Including mortgage payments, loan interest, or debt service in operating expenses — NOI is an unlevered metric that must exclude all financing costs, so the property can be compared regardless of how it is funded.
    • Using gross rental income without subtracting vacancy and credit loss — even well-managed properties have some vacancy; using 100% occupancy overstates NOI and makes the investment look better than it is.
    • Forgetting capital expenditures (CapEx) vs. operating expenses — a new roof is a capital expense, not an operating expense, and including it in the NOI calculation artificially depresses the NOI for that year.
    • Double-counting property management fees — if you self-manage, you should still include a market-rate management fee (typically 8-12% of gross rent) to get a realistic NOI that reflects true operating costs.
    • Using projected rents instead of actual or verified market rents — sellers and brokers often present optimistic rent assumptions that inflate NOI beyond what the property will actually produce.

    Frequently Asked Questions

    Why is NOI so important?

    NOI is the foundation for property valuation (via cap rate), loan qualification (DSCR), and measuring property performance. It isolates operating performance from financing decisions.

    What is NOT included in operating expenses?

    Mortgage payments (principal and interest), capital expenditures, depreciation, and income taxes are excluded from operating expenses when calculating NOI.

    How can I increase NOI?

    Increase income by raising rents, adding revenue streams, or reducing vacancy. Decrease expenses through better management, energy efficiency, tax appeals, or competitive bidding for services.

    Ready to run the numbers?

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