Commercial Lease Types: Gross, Modified Gross, and NNN Explained

Lease structure is one of the most underappreciated variables in commercial real estate underwriting. Two buildings can sit side by side, charge identical rent, and produce dramatically different NOI — and therefore dramatically different valuations — based entirely on who is responsible for paying operating expenses.

When I first started evaluating commercial projects, I made the same mistake many newer investors do — I focused almost entirely on rent per square foot. It didn't take long to realize that who pays the expenses often matters just as much as the rent itself.

For investors underwriting an acquisition, lease structure determines how much of gross rent actually reaches the bottom line. For developers, it affects projected NOI, financing assumptions, and tenant mix decisions that should be made during planning — not after construction.

This guide covers the full spectrum: gross, modified gross, NNN, percentage rent, and ground leases — with examples of how each affects NOI and value. For a deep dive on underwriting a specific NNN acquisition, see How to Analyze a NNN Lease Investment.

The Three Primary Lease Structures at a Glance

These categories are not rigid. Modified gross leases in particular vary significantly from deal to deal — the specific expense allocation is negotiated and written into each lease. Reading the lease carefully is not optional.

Gross Lease

In a gross lease, the tenant pays one monthly rent amount. The landlord handles everything else.

From the tenant's perspective, a gross lease offers simplicity and predictability. They know exactly what occupancy costs each month. From the landlord's perspective, it creates expense risk — rising taxes, insurance premiums, or unexpected maintenance come out of the landlord's income.

Gross Lease NOI Example

Notice the leverage in the wrong direction: if property taxes increase 10%, that is a $720 hit to the landlord's income with zero ability to pass it through until lease renewal.

Where Gross Leases Make Sense

Gross leases are most common in professional and medical office buildings, where tenants expect a predictable, all-in occupancy cost. They are also standard in markets where smaller office users have historically set expectations that way.

Modified Gross Lease

Modified gross sits between gross and NNN. Some expenses remain with the landlord. Others shift to the tenant. The specific allocation is negotiated for each lease.

A typical modified gross structure might look like this — but this is not a standard. Every deal is different.

Modified gross leases give landlords flexibility. You can remain competitive in markets where tenants resist NNN leases while still protecting yourself from controllable operating costs. Multi-tenant office buildings frequently use some variation of modified gross.

The critical point: when reviewing or drafting a modified gross lease, the expense allocation must be explicitly specified. Modified gross is a category, not a standard. Two modified gross leases in the same building can have completely different structures. This is also relevant at acquisition — if you're buying a building with existing modified gross leases, verify the actual expense split on each one before underwriting.

Triple Net (NNN) Lease

In a triple net lease, the tenant pays base rent plus the three nets: property taxes, building insurance, and common area maintenance (CAM).

The landlord still owns the building and typically remains responsible for the roof and structural elements — though in an absolute NNN lease, even those pass to the tenant. The practical result: the landlord's operating expense exposure is minimal.

What Is CAM?

CAM (Common Area Maintenance) covers the shared costs of operating the property — parking lot maintenance, landscaping, snow removal, exterior lighting, common hallways, and similar items. In NNN leases, CAM charges are billed to tenants as a separate line item, often reconciled annually against actual expenses.

CAM charges are typically estimated at the start of each year and reconciled once actual expenses are known. If actual costs exceed the estimate, tenants receive an additional bill; if costs come in lower, they receive a credit. This reconciliation process can be a point of friction — especially when tenants receive an unexpected year-end charge. Some landlords cap annual CAM increases (a “CAM cap”) to give tenants more cost predictability while still passing through most of the actual expense increases.

NNN NOI Example

Tenant also pays taxes, insurance, and CAM directly. The landlord's remaining expenses are limited to reserves for roof and structural maintenance.

This is why NNN properties often attract passive investors — the income is relatively predictable and management-light, particularly when the tenant is a national credit-rated company on a long-term lease.

Common NNN Tenant Types

For a full framework on underwriting a single-tenant NNN acquisition — including tenant credit analysis, dark risk, and rent bump modeling — see How to Analyze a NNN Lease Investment.

Same Rent, Completely Different NOI

This is the comparison most investors find clarifying. Two buildings, identical square footage, identical headline rent — different lease structures.

The value difference is not trivial. At a 6% cap rate, $27,000 in additional annual NOI translates to $450,000 in property value — on the same physical building charging the same rent.

This matters for acquisitions — comparing two commercial properties without understanding their lease structures is an incomplete comparison. It matters equally for development underwriting, where the projected lease structure drives the pro forma NOI that supports your construction financing.

How Lease Structure Affects Property Value

Commercial real estate is valued primarily on NOI and cap rate. Because lease structure directly determines NOI, it directly determines value. Even modest changes in annual NOI produce large changes in value at typical commercial cap rates.

This dynamic compounds over time. NNN leases with annual rent escalations — commonly 2% per year or 10% every five years — grow NOI predictably without any corresponding increase in landlord expenses, since those pass through to the tenant. That steady NOI growth drives value creation even without market cap rate compression.

For cap rate benchmarks by property type and lease structure, see What Is a Good Cap Rate for Commercial Real Estate.

Percentage Rent Leases

Not every commercial lease fits neatly into gross or NNN. Retail centers frequently use percentage rent clauses — a hybrid structure where the tenant pays base rent plus a percentage of gross sales above a negotiated threshold.

Percentage rent aligns landlord and tenant interests — the landlord benefits when the tenant performs well. It's most common in shopping centers, outlet malls, entertainment venues, and restaurants. It is rarely used in industrial, office, or single-tenant standalone retail.

Ground Leases

Ground leases are structurally different from the lease types above. In a ground lease, the tenant leases the land only, then builds and owns the improvements themselves. At lease expiration, the improvements typically revert to the landowner.

Ground leases commonly run 30–99 years. They are frequently used by national tenants — banks, fast food chains, gas stations — who want to control the building but not own the underlying land.

For landowners, ground leases can produce long-term passive income with minimal involvement. The underwriting focus shifts from NOI and expenses to the credit of the tenant, the terms of reversion, and the land's long-term value. Ground leases are less common for smaller investors but worth understanding when evaluating certain types of commercial land.

Which Lease Structure Should You Use?

Market conditions and local norms matter. In tight markets where tenants have leverage, gross or modified gross leases may be necessary to attract occupancy even for product that would typically command NNN terms. In markets with strong tenant demand, NNN is achievable for nearly any commercial property type.

Lease Structure Isn't Everything

The best lease structure in the world doesn't help if the building sits vacant. Tenant quality, lease length, rent escalation schedules, and the initial tenant improvement package all affect returns just as significantly as whether the lease is gross or NNN.

When underwriting a commercial acquisition, model the lease structure before you start comparing cap rates or running financing scenarios. If your expense assumptions are wrong, everything downstream is wrong too.

A NNN lease with a marginal local tenant on a short remaining term carries substantially more risk than a gross lease with a creditworthy regional anchor on a 10-year term. Lease structure affects expenses. Tenant quality and term affect income security.

For how tenant improvement decisions interact with lease structure — including how much buildout to offer and how to protect yourself — see Vanilla Shell vs. Tenant Improvements. For flex and light industrial specifically, How to Analyze a Flex Space Investment covers the full underwriting framework.