What net operating income is, and what it deliberately leaves out
Net operating income is what a property earns from its own operations in a year, before anything to do with how it was bought. It is the profit the building would generate for any owner, financed or not, which is precisely why it is the currency of commercial real estate: brokers quote it, appraisers capitalise it, and lenders divide it by debt service to decide how much they will lend.
Four things are excluded by definition, and each exclusion has a reason:
- Mortgage principal and interest. These belong to your capital structure, not the property. Leaving them out is what makes NOI comparable between a cash buyer and a leveraged one.
- Capital expenditure. A new roof is a lumpy investment that extends the asset's life, not a cost of this year's operations. The smoothed annual equivalent — a replacement reserve — does belong in.
- Depreciation and amortisation. Accounting entries with no cash movement.
- Income tax. It depends on the owner's situation, not the building's.
Everything else that keeps the building running is in: property taxes, insurance, owner-paid utilities, management, repairs, landscaping, pest control, turnover costs, legal, accounting and licences. Get the boundary right and NOI is the most useful single number in the analysis. Get it wrong — most often by leaving the mortgage in or the management fee out — and every metric built on top of it inherits the error.
From gross scheduled rent down to NOI, line by line
The statement runs top to bottom in a fixed order, and the order matters because two lines are percentages of intermediate totals.
Gross scheduled rent is the rent roll at full occupancy and market rent for twelve months. Note that this is market rent, not the rent currently contracted. The difference between them is loss to lease, and on a property with long-tenured tenants it can be large.
Vacancy and credit loss is a percentage of gross scheduled rent covering physical vacancy, turnover downtime and tenants who do not pay. Use the submarket's actual rate rather than the property's current one when the current one is temporary. Model it in detail with the vacancy loss calculator.
Other income is added after the vacancy deduction, not before it, because laundry and parking revenue is not scheduled rent and does not vanish at the same rate. Add it net of the direct cost of providing it if that cost is not already in your expense lines.
Effective gross income is the result, and it is the correct denominator for two things: the management fee, and the operating expense ratio. Property managers charge on collections, so a fee quoted at 6% is 6% of EGI. Charging it on gross scheduled rent overstates the expense by exactly the vacancy rate — on a 5% vacancy assumption, a 6% fee computed on the wrong base is 5% too large.
Operating expenses are subtracted to give NOI. The replacement reserve is the one line practitioners disagree about; see the callout below.
Worked example: an eight-unit building
Eight units at $1,375 a month give gross scheduled rent of 8 × 1,375 × 12 = $132,000. Laundry and parking add $6,000. The submarket runs 5% vacancy. Management charges 6% of collections, and you carry a $300 per unit annual reserve.
- Vacancy and credit loss. 132,000 × 0.05 = $6,600.
- Effective gross income. 132,000 − 6,600 + 6,000 = $131,400.
- Management fee. 131,400 × 0.06 = $7,884.
- Replacement reserve. 300 × 8 = $2,400.
- Total operating expenses. 14,000 taxes + 5,200 insurance + 6,000 utilities + 7,884 management + 9,000 repairs + 2,400 reserve = $44,484.
- Net operating income. 131,400 − 44,484 = $86,916.
- Operating expense ratio. 44,484 ÷ 131,400 = 33.9%.
- Per unit. Expenses 44,484 ÷ 8 = $5,560.50; NOI 86,916 ÷ 8 = $10,864.50.
Two things fall straight out of that NOI. At a 6.5% market cap rate the building is worth 86,916 ÷ 0.065 = $1,337,169. And a lender requiring a 1.25 debt service coverage ratio will support annual debt service of 86,916 ÷ 1.25 = $69,533, which at a 6.5% thirty-year constant of about 7.58% implies a loan near $917,000. Both figures move dollar for dollar with any error in the expense lines.
The reserve line is where two honest people disagree
The Appraisal Institute treats a replacement reserve as an operating expense; most broker offering memoranda do not include one. On the example above, the $2,400 reserve is the difference between an NOI of $86,916 and one of $89,316, and at a 6.5% cap rate that is a $36,923 difference in value. Neither convention is wrong, but comparing your reserve-inclusive NOI against a broker's reserve-free one will make every listed property look overpriced by roughly the capitalised value of the reserve. State your convention and apply it to both sides.
How to read the operating expense ratio
Once you have NOI, the diagnostic worth reading next is the operating expense ratio: total operating expenses as a share of effective gross income. It is the fastest way to tell whether an expense statement is complete.
What the ratio should be depends almost entirely on who pays the utilities and how heavy the property tax burden is, so there is no single correct figure. What is reliable is the direction of the tells:
- A very low ratio usually means a missing line, not an efficient building. Management, reserves and a reassessed property tax bill are the three most commonly absent. Add them back before concluding anything.
- Owner-paid heat moves the ratio a long way. A master-metered building and an individually-metered one are not comparable on this measure at all.
- Compare per-unit dollars as well as percentages. Expense per unit is insensitive to your rent assumption, so it catches errors the ratio hides. If your expenses per unit are far below what comparable buildings in the same market run, you have found the problem.
Track the ratio on its own with the operating expense ratio calculator, and remember that everything downstream depends on it: NOI feeds the cap rate calculator, the DSCR calculator and the rental cash flow calculator.
How each expense line moves NOI and value
| Expense line | Amount | % of EGI | Per unit | Value impact at 6.5% |
|---|---|---|---|---|
| Property taxes | $14,000 | 10.7% | $1,750 | $215,385 |
| Insurance | $5,200 | 4.0% | $650 | $80,000 |
| Owner-paid utilities | $6,000 | 4.6% | $750 | $92,308 |
| Management at 6% of EGI | $7,884 | 6.0% | $986 | $121,292 |
| Repairs and maintenance | $9,000 | 6.8% | $1,125 | $138,462 |
| Replacement reserve | $2,400 | 1.8% | $300 | $36,923 |
| Total | $44,484 | 33.9% | $5,560 | $684,369 |
The value impact column is the expense divided by 0.065 — the amount of value that line destroys when capitalised. It is why a $1,000 annual error in an expense estimate is a $15,385 error in what the building is worth.
Errors that corrupt an NOI figure
- Including the mortgage. Principal and interest are not operating expenses. This single error typically cuts a correct NOI by half or more and makes the property look unfinanceable.
- Charging the management fee on gross scheduled rent. Managers charge on collections. At a 5% vacancy assumption, using scheduled rent as the base overstates the fee by 5%.
- Carrying the seller's property tax bill. Many jurisdictions reassess on transfer. Underwrite the tax the new assessment will produce, and check the assessor's methodology with the property tax millage calculator.
- Omitting management because you self-manage. Your time has a market price, and the next buyer will underwrite the fee. An NOI without it is not a market NOI.
- Counting a capital project as an operating expense. A $40,000 roof replacement does not belong in NOI. The annual reserve that anticipates it does.
- Adding other income before deducting vacancy. Laundry income does not disappear at the residential vacancy rate. Deduct vacancy from scheduled rent, then add other income.
- Using current contract rents as gross scheduled rent without saying so. Below-market in-place rents produce a true but non-market NOI. Report both, and label which is which.
Where NOI goes next
NOI is not an endpoint. It is the input to almost everything else in commercial real estate analysis.
Value. Divide NOI by the market cap rate and you have the income approach to value. This is the mechanism by which a $1,000 saving in annual expenses creates roughly $15,000 of value at a 6.5% cap — the reason operational improvements are worth so much more than they cost.
Loan sizing. Lenders divide NOI by required debt service coverage to get maximum annual debt service, then convert that to a loan amount at the quoted constant. NOI, not your income, is what qualifies a commercial property.
Cash flow. Subtract actual debt service from NOI and you have pre-tax cash flow, the numerator of cash-on-cash return.
Two conventions to keep straight. First, NOI is not EBITDA, although they rhyme: EBITDA is a corporate measure that adds depreciation back to accounting profit, while NOI is a property-level cash measure that never counted depreciation in the first place, and NOI conventionally includes a reserve that EBITDA does not. Second, in triple-net commercial leases the tenant pays taxes, insurance and maintenance directly, so the landlord's NOI is close to the base rent and the expense ratio is very low by construction — see the triple net lease calculator rather than comparing such a property against a gross-lease apartment building.