📖 Commercial lease glossary
Modified Gross Lease
A modified gross lease is a hybrid: the landlord pays a defined basket of operating expenses up to the level those costs ran in a named base year, and the tenant reimburses its pro-rata share of what the same basket costs above it. The tenant pays base rent plus a growth charge, not the full expense load as under a triple net lease. Because every reimbursement is measured against the base-year figure, how that number was chosen decides more of the deal than the rent does.
How the hybrid splits the bill
Under a modified gross lease the expense obligation is split by threshold rather than by category. The landlord absorbs the agreed basket — usually real estate taxes, insurance, and CAM, sometimes building utilities — at the level it cost in the base year; the same basket in any later year, to the extent it exceeds that figure, is billed to tenants pro rata as additional rent. The tenant never pays the first $9.80/SF, only the growth on top.
Both sides keep something. The tenant's exposure is limited to increases over a number fixed at signing, rather than to a full expense stack that can rise in absolute dollars. The landlord gets partial inflation protection and a lower headline rent than a true gross quote would require.
Base year mechanics, and the annualization trap
The base year is defined one of two ways. Most office leases pick the first year of the term, either the calendar year in which commencement falls or the twelve months beginning there. Others name a fixed calendar year regardless of when the tenant moves in, which anchors the reference number on actuals already on the books instead of an estimate the landlord will have to defend later.
A mid-year commencement is where the errors concentrate. If the term starts on October 1 and the base year is the calendar year of commencement, the reference period is a year in which the tenant held the space for three months while the landlord incurred twelve months of expense. Leases handle that by annualizing the base period to a full year, and the step can move the number a lot: a quarter that caught a seasonal utility cycle, a partial lease-up, or a deferred repair annualizes into a reference figure with little relation to what the building will cost to run. Every reimbursement bill for the rest of the term is measured against it.
- ✓Annualization method — straight multiplication of the partial period versus an occupancy-adjusted figure; two leases with identical expense records can produce different base numbers
- ✓Gross-up of the base year — restating variable costs in the base period to a stipulated occupancy raises the threshold and protects the tenant from a cheap, half-empty reference year
- ✓Base year reset at renewal — many clauses reset the base year to the year before the option term, erasing accumulated exposure; capture it as its own dated field
Worked example: base year $9.80/SF growing to $11.35/SF
A 10,000 SF tenant in a 100,000 SF building — a 10% pro-rata share — signs a modified gross lease with a base-year basket of $9.80/SF, meaning $980,000 of taxes, insurance, and CAM for the building in the reference year, plus a clause requiring reimbursement of increases over it. (All numbers hypothetical.)
In year three a tax reassessment and a reinsurance cycle take the same basket to $1,135,000, or $11.35/SF. The increase over the base year is $1.55/SF, and the tenant pays its pro-rata share of that delta: $1.55 x 10,000 SF = $15,500 for the year, roughly $1,292 a month, as additional rent. It pays none of the first $9.80/SF, which stays the landlord's cost unless the base year resets.
On the annual statement that line is usually labeled "pass-throughs above base year." It is not the tenant's full expense allocation: it is (current-year basket minus base-year basket) x pro-rata share. A checkable statement shows the base year used, the current-year basket total, and the pro-rata percentage with its square-footage basis. A line that only says "OpEx recovery $15,500" is a request for the build-up, not a payment instruction.
Expense stop vs. base year, and what to abstract
A base year and an expense stop do the same job by different routes. A base year is a period whose actual expenses become the threshold after the fact; an expense stop is a dollar figure per square foot written into the lease, known at signing and independent of any year's books. They often coincide numerically, which is why the terms get swapped — and why an abstract recording "stop: $9.80" without saying which kind of stop it is can misprice the tenant's exposure.
- ✓Base year — which year, calendar or lease year, whether a partial period was annualized, and whether it resets at renewal or on an assignment
- ✓Included basket — the categories the landlord absorbs up to base level and on which the tenant pays growth; the same rent and base year with a different basket is a different deal
- ✓Exclusions — capital expenditures, leasing commissions, debt service, and often management fee increases sit outside the basket, moving both the base-year figure and every later comparison
- ✓Annualization method — the formula that turns a partial base period into a full-year reference number, quoted from the lease rather than summarized
- ✓Tax stop versus combined stop — whether real estate taxes run through the same threshold or carry their own base year, plus the statement timing and tenant audit window that make the number checkable
Frequently asked questions
What is the difference between a modified gross lease and a full-service gross lease?
A full-service gross lease has the landlord pay the defined categories with no reimbursement obligation at all. A modified gross lease prices the same basket but requires the tenant to reimburse increases over a base year or expense stop. In listings, "gross" very often means modified gross; the tell is any reference to a base year, a stop, or "in excess of base year" in the rent or expense article.
Why does the base year matter for the first CAM bill?
The base year sets the threshold the first reimbursement is measured against, and in the base year itself there is normally nothing to bill. A pass-through charge appearing in the first year is a flag: the base-year figure was set below what the building immediately cost — a fixed calendar year, or an annualized partial period that understated actual cost.
How is the base year annualized on a mid-year start?
Take a commencement on October 1 where the basket cost $245,000 across the building in that base period. Annualized, that is $245,000 x 4 = $980,000, or $9.80/SF in a 100,000 SF building, and it becomes the stop for the rest of the term. If the quarter ran light on variable costs, the season is baked into the reference permanently — hence the tenant ask for a fixed calendar base year already in the books.
Is an expense stop the same as a base year?
Same effect, different documents. An expense stop is a negotiated dollar rate stated in the lease — the landlord absorbs costs up to $9.80/SF whatever the books show — so it is known at signing and cannot drift. A base year is a reference period whose actual expenses set the threshold once the year closes, which makes it depend on the landlord's accounting, including annualization and gross-up.
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