Key Takeaways
A lender's NOI is built from verified income, not quoted income. Base rent is checked against leases and operating statements, and other income is credited only when it is documented and has a collection history.
Vacancy and expense adjustments tend to pull the number below the pro forma. Lenders usually apply a vacancy allowance even to a fully leased building, and they add costs sellers often leave out, such as management, replacement reserves, and reassessed property taxes.
A lower underwritten NOI means a smaller loan and a lower implied value. Loan size depends on the cushion between income and debt service, and a cap rate ties NOI directly to price.
Two people are looking at the same building. The seller's broker takes the rent roll, multiplies the monthly rent by twelve, subtracts a handful of bills, and arrives at a net operating income that makes the asking price look reasonable. The lender, working from the same documents, arrives at a lower number. The loan is sized off the lender's number, not the broker's.
Neither person is necessarily wrong about the arithmetic. They are answering different questions. The broker asks what the property would earn if everything goes as planned. The lender asks what the property can be shown to earn, and whether that income would still cover the loan if things go somewhat worse.
Base rent is where the calculation starts, not where it ends
Base rent is the contractual rent tenants pay under their leases, before anything is added or taken away. It is the cleanest line in the file, which is why it gets quoted so often. But a lender treats it as a claim to be verified.
Underwriters compare the rent roll against the leases themselves and against recent operating statements. They look for rent that is quoted but not being collected, free-rent periods, scheduled step-ups that have not happened yet, and tenants whose leases expire soon. They also compare in-place rents with what similar space is actually leasing for. If a unit's rent is well above the market, the lender may not assume it will last.
From base rent to gross income
Gross income is broader than base rent. It generally adds other income the property produces, such as expense reimbursements from tenants, parking, storage, laundry, or fees. Lenders are selective about these items. Reimbursements that are written into leases and have a history of being collected are easier to credit than a line labeled "other" with no support.
Underwriters usually distinguish between potential gross income, meaning what the property would produce if fully occupied and everyone paid, and effective gross income, meaning what remains after losses. That gap is where the next adjustment comes in.
The vacancy factor
A pro forma often assumes the building is full. A lender usually does not. It applies a vacancy factor, an allowance for income lost to empty space and to tenants who pay late or not at all.
The allowance is often applied even when the building is fully leased today. Leases end, tenants leave, and re-leasing takes time. The lender is sizing a loan that will last for years, not for the current month. Where actual vacancy is higher than a typical allowance, lenders generally use the higher figure. In agricultural settings, the equivalent question is how dependable the income is from year to year, given crop prices, yields, water supply, and lease structure.
The expense ratio and the expenses behind it
After vacancy, the lender subtracts operating expenses. The expense ratio expresses those expenses as a share of effective gross income. Lenders use it as a reasonableness test. If a borrower's statement shows expenses far below what comparable properties typically run, the underwriter is likely to suspect that something is missing and adjust upward.
The usual gaps are:
Property taxes. In California, a sale can lead to reassessment, so the seller's current tax bill may not be the buyer's future one.
Management fees. An owner who manages the property personally still has a management cost. Lenders typically include one, because a future owner or the lender itself may need to pay for professional management.
Repairs and maintenance. A year with unusually low repair spending does not mean the building needs no repairs.
Insurance and utilities. Costs that have changed recently may not appear in older statements.
Replacement reserves. Many lenders deduct an allowance for roofs, paving, and mechanical systems that wear out over time, even though the cost does not occur every year.
Debt service is not an operating expense. Neither are income taxes or depreciation. Leaving them out is deliberate, because net operating income is meant to measure what the property earns independent of how it is financed or how the owner is taxed.
Putting it together
The sequence, in plain terms:
Start with verified base rent.
Add supportable other income to reach gross income.
Subtract a vacancy factor to reach effective gross income.
Subtract operating expenses, tested against the expense ratio and expected costs.
The result is the lender's net operating income.
Each step involves judgment, and each judgment tends to move the number down rather than up. That is why the lender's figure so often comes in below the one on the marketing materials.
Why the number matters for the loan
The lender's net operating income feeds directly into how much can be borrowed. Lenders commonly test it against the loan's annual debt service, a measure called the debt service coverage ratio. A larger cushion between income and the loan payment gives the lender more room if income falls. Because the loan size depends on that cushion, a lower underwritten NOI means a smaller loan for the same property and the same interest rate.
The same number affects value. Since a cap rate relates NOI to price, a lower NOI implies a lower value at any given cap rate. A buyer who paid a price based on a seller's NOI may find that the lender's view of value, and therefore the loan, is lower than expected.
What borrowers can do with this
It helps to build your own numbers the way a lender will. Reconcile the rent roll to the leases and to actual deposits. Use a realistic vacancy factor. Include every expense a new owner would bear, and compare your expense ratio with what similar properties run. Then look at the gap between your figure and the pro forma you were given. The gap shows how much of the seller's number is assumption.
This article is general educational information. It is not legal, tax, accounting, or investment advice, and underwriting practices vary by lender and by property.