NNN vs gross lease: who carries the expense risk
The offering memorandum arrives Friday afternoon with a rent roll that mixes lease types. Two tenants pay a quoted rent "NNN." One pays "full service gross." A fourth has a "modified gross" lease with a base year, and the broker's pro forma shows a single NOI number that does not tell you which expense dollars the landlord actually owns. Your lender wants the cash flow by Monday, and the lease abstracts are still in a shared folder.
Quoted rents are not comparable across lease types. A $24 net rent and a $32 gross rent can produce the same NOI in year one and very different NOI in year five. The difference sits in who pays for taxes, insurance and common area maintenance when those costs move.
By the end of this article you will be able to model NNN, gross and modified gross leases side by side and see exactly how each one changes recoveries, NOI and the cash flow you underwrite.
The core distinction is simple. Under a net lease the tenant reimburses the landlord for some or all operating expenses on top of base rent. Under a gross lease the tenant pays one rent and the landlord pays the expenses out of it. A modified gross lease sits between the two, usually by passing through only the increases above a defined starting level.
The NNN vs gross lease question is therefore a question about expense risk. Under NNN the tenant carries most of it. Under gross the landlord carries all of it. Under modified gross the risk is split at a threshold you have to find in the lease.
Underwriting a triple-net lease
In a triple-net lease the tenant pays base rent plus its pro rata share of property taxes, insurance and common area maintenance. The landlord collects those reimbursements as expense recoveries. In your model they appear as revenue lines above the operating expense lines, not as a reduction of expenses.
That presentation matters. Effective gross income (EGI) includes base rent and recoveries. Operating expenses include the full expense pool. NOI is EGI minus operating expenses, so a fully recovered expense pool nets to zero and NOI approaches base rent.
Triple-net lease underwriting needs more than a single "NNN" flag. For each tenant you need:
- the pro rata share, and whether it is based on leased or total building area;
- which expense categories are recoverable and which are excluded;
- any cap on controllable expense growth;
- any administrative fee the landlord may charge on top of the pool;
- whether recoveries are billed monthly on an estimate and reconciled after year-end.
The last point is a timing issue. Estimates billed during the year are trued up later, so the cash you receive and the expense you accrue do not always land in the same period. Model the reconciliation if the lease provides for one.
Underwriting a gross lease
Gross vs net lease NOI is the comparison most brokers skip. A gross lease bundles expense reimbursement into the rent, so the rent line looks larger and the expense lines look larger by the same amount. Strip out the embedded expense component before you compare any gross rent to a net rent.
A gross lease has one rent figure, and the landlord pays the operating expenses. There are no recoveries, so EGI is base rent less vacancy and credit loss. Expenses sit entirely below the line.
This makes year-one NOI easy to compute and makes the forward years more fragile. If taxes, insurance and maintenance grow faster than the contractual rent escalations, the landlord's margin compresses with no offset. A gross lease with flat or lightly escalating rent is effectively a short position on expense inflation.
When you underwrite a gross lease, the expense growth assumption deserves as much scrutiny as the rent growth assumption. Run both on the same timeline. Then test what happens when expenses grow faster than your base case, which is the stress test you would use on any NOI line, such as the sensitivity grid in a commercial real estate financial model.
Modified gross leases: base years and expense stops
A modified gross lease usually includes a base year or an expense stop. Under a base year, the landlord pays the operating expenses incurred in a stated year. The tenant then reimburses its share of any increase above that base in later years. An expense stop works the same way but fixes the threshold at a stated amount per square foot instead of an actual year.
The modeling mechanic is a recovery formula: the tenant's share multiplied by the greater of zero and the current year's expenses less the base amount. Because the recovery only starts when expenses exceed the stop, the landlord still carries the starting expense level and all of the risk below it.
Three details change the answer:
- The base year choice. A base year set in a year with abnormally low expenses leaves the landlord carrying a larger share of later costs.
- Gross-up provisions. Some leases adjust variable expenses in the base year to reflect full occupancy, which affects the threshold.
- Expense definitions. The base amount and the current-year amount must be measured on the same category definitions, or the increase is overstated or understated.
Read the lease language rather than the abstract, and confirm any ambiguous clause with the property's counsel. The label "modified gross" covers many different arrangements.
Worked example: one building, three lease structures
Every number below is an example input chosen for round arithmetic. It is an illustration of method, not a market observation.
Assume a 10,000 SF single-tenant building. Annual operating expenses (taxes, insurance, common area maintenance) are $80,000 in year one, or $8.00 per SF. In year two they rise to $84,000. Assume no vacancy or credit loss so the comparison isolates the lease structure.
| NNN | Gross | Modified gross (base year) | |
|---|---|---|---|
| Base rent, year one | $240,000 ($24.00/SF) | $320,000 ($32.00/SF) | $300,000 ($30.00/SF) |
| Recoveries, year one | $80,000 | $0 | $0 |
| Operating expenses, year one | $80,000 | $80,000 | $80,000 |
| NOI, year one | $240,000 | $240,000 | $220,000 |
| Recoveries, year two | $84,000 | $0 | $4,000 |
| Operating expenses, year two | $84,000 | $84,000 | $84,000 |
| NOI, year two | $240,000 | $236,000 | $220,000 |
The NNN and gross structures are set to produce identical year-one NOI, which is why quoted rents alone tell you nothing. In year two the $4,000 expense increase is fully passed through under NNN, borne entirely by the landlord under gross, and passed through under the modified gross lease because it exceeds the $80,000 base. The modified gross lease has a lower NOI in this example only because its example rent is lower, not because of the structure.
Now carry the difference into value. At an example 7% cap rate, a $4,000 NOI gap capitalizes to roughly $57,000 of value (4,000 ÷ 0.07). Your direct capitalization method is only as reliable as the NOI behind it, and lease structure determines how stable that NOI is when costs move.
Where the structure breaks the model
Clean examples hide the places where real leases diverge. Check these before you trust a recovery line.
Vacancy. Under a net lease the tenant pays its pro rata share. If part of the building is empty, the landlord absorbs the unoccupied share of the expense pool. In the example, if 20% of the area went vacant, the landlord would carry 20% of $80,000, or $16,000, on that space. Recoveries must scale with occupancy, not with the full pool.
Non-recoverable expenses. Capital reserves, certain management costs and some repairs are often excluded from recoveries. Keep them in a separate line so NOI shows what the landlord keeps.
Caps and exclusions. A cap on controllable expense growth limits recoveries even when actual costs rise faster. The shortfall falls to the landlord.
Reconciliation timing. Recoveries billed on estimates and settled later create a receivable or a refund liability.
Lease expiry. Structure often changes at renewal. A tenant on a gross lease may renew on a net basis, or the reverse, which changes both the rent and the recovery assumptions for the renewal period. Tie each assumption to the tenant's lease expiry date on a rent roll that records structure, share and recovery terms.
Building the comparison in your model
When you compare an NNN vs gross lease on the same property, hold everything else constant: same area, same expense pool, same vacancy and same growth rates. Change only the recovery mechanics. The difference in NOI across years is then attributable to the structure, which is the number your lender and your investment committee will ask for.
The practical goal is to run every tenant through the same cash flow logic and let the lease terms drive the differences. That means a tenant-level schedule with base rent, escalations, recoverable expense categories, pro rata share, base year or stop, caps and fees. Recoveries then compute from the building's expense pool rather than being typed in as a plug.
Check the output against a simple NOI calculator at the property level. If total recoveries plus base rent minus total expenses does not reconcile to your NOI, one of the lease terms is mis-entered.
The Commercial Lease Underwriting model is a NNN, gross, and modified gross lease cash flow model with a TI and commission schedule. It ships fully unlocked with methodology documentation, so you can trace every recovery calculation. For a whole-asset acquisition view with a tenant rent roll, lease expiry, DSCR and sensitivity, see The Commercial Sheet.
To start with the structure of the cash flow, download the free 3-tab Starter Pro Forma from the lead magnet page. When you are ready to model lease-by-lease recoveries, the Commercial Lease Underwriting model is built for it.
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