Gross and modified gross leases still pass cost increases to the tenant. The base year or expense stop decides where your share starts, and a few California details can move that line.
In a gross or modified gross lease, a base year sets the starting line at what the building actually costs in a chosen year. An expense stop sets that line at a fixed dollar amount per square foot instead. The tenant pays its share of costs above the line. Base year vs expense stop comes down to who bears the risk that the starting number is wrong.
Key takeaways
- A base year uses actual first-year costs as the threshold. An expense stop uses a negotiated fixed amount per square foot.
- A stop set below real first-year costs means the tenant starts paying increases on day one.
- Base years should be “grossed up” for occupancy, meaning variable costs are adjusted to a set occupancy level. The AIR office gross form uses 95%.
- In California, a temporary Proposition 8 tax reduction or a Proposition 13 reassessment after a sale can distort a base year.
- Many California industrial gross leases apply a base only to property taxes and insurance and pass common area costs through in full.
Base year vs expense stop at a glance
| Feature | Base year | Expense stop |
|---|---|---|
| How the threshold is set | Actual expenses in a named year | Fixed dollar amount per SF in the lease |
| When you know the number | After the base year closes | At signing |
| Tenant’s main risk | An artificially low base year | A stop set below real costs |
| Landlord’s main risk | An unusually high base year | A stop set above real costs |
| Where you see it | Multi-tenant office, some flex | Office and some modified gross deals |
What is the difference between a base year and an expense stop?
Both tools answer the same question in a gross lease: how much of the building’s operating cost is built into the rent, and how much of any increase does the tenant pay? (For how gross leases compare with other structures, see our guide to NNN, modified gross and full-service leases.)
The CCIM Institute defines an expense stop as the level up to which the landlord pays certain operating expenses, with amounts above it the tenant’s responsibility, as PropertyMetrics cites it. A base year is a stop set after the fact. The threshold equals whatever the building costs in the base year, usually the calendar year the lease starts. A fixed expense stop is written into the lease as a dollar figure before anyone knows what that year will cost.
How does a base year work?
A base year makes the tenant responsible only for the growth in expenses. The AIR Standard Multi-Tenant Office Lease – Gross shows the mechanics. The tenant pays its share of the amount by which operating expenses in each comparison year exceed those in the base year. Expenses are calculated as if the project were at least 95% occupied, so a partly empty building does not set an artificially low base.
Office rents are commonly quoted gross. National brokerage market reports for Q2 2026 quote office asking rents on a gross basis, so most office tenants live with a base year whether they think about it or not.
How does an expense stop work?
An expense stop works like a deductible. With a fixed stop, the lease names a number, such as $2.40 per square foot per year. If actual expenses come in at $2.60, the tenant pays its share of the $0.20 difference. If expenses come in lower, the tenant usually pays nothing extra and gets no credit.
The danger is in how the number is chosen. A stop based on last year’s costs, or on an optimistic budget, can sit below what the building will cost in your first year. You then pay increases from the first statement, with no real cushion.
How do California industrial gross leases handle rising costs?
Many California industrial gross leases use a narrower base that covers only taxes and insurance. Under the November 2017 AIR Standard Industrial/Commercial Multi-Tenant Lease – Gross, the tenant pays its share of common area operating expenses in full. It also pays any increase above the Base Real Property Taxes, which are the taxes for the calendar year the lease is signed, and any Insurance Cost Increase above the Base Premium. AIR defines the base premium as the premium for the 12 months before the lease start date.
AIR describes its single-tenant gross form the same way: the tenant pays increases in property taxes and insurance after the first year and reimburses the landlord for maintaining the building. For a small unit in a Bakersfield or Shafter business park, that can look a lot like a NNN lease with a cushion on two line items. Brokers often call this structure an “industrial gross” lease, though local usage varies, and the expense paragraph is what sets the real cost. Our explainer on operating expense pass-throughs covers the line items, and our CAM reconciliation guide shows how the year-end bill is built.
What can go wrong with a base year in California?
Anything that makes the base year unusually cheap raises what you pay later. California property tax rules create two specific traps, and building operations create two more.
- Proposition 8 reductions. If the county assessor temporarily lowered the assessment for a decline in value, the State Board of Equalization explains that the value can later rise by more than 2% a year until it reaches the factored base year value. A low-tax base year then produces outsized increases. See the board’s decline-in-value page.
- A sale during your term. Under Proposition 13, a change in ownership resets assessed value to market. Most leases count that higher tax as an increase over the base, and the AIR multi-tenant net form expressly includes change-of-ownership increases in its tax definition. Our guide to Prop 13 reassessment explains the trigger.
- Low occupancy. Without a gross-up, variable costs in a half-empty building understate what a full building costs. Holland & Hart notes that parties negotiate gross-ups at 95% or 100% occupancy, and that fixed costs such as taxes and insurance should not be grossed up.
- Deferred costs. Skipped maintenance, an insurance policy renewed just after the base year or a delayed service contract all shrink the base.
Base year vs expense stop: which is better for a tenant?
A base year is usually more tenant-friendly because it is tied to real costs. A fixed stop can work if it sits at or above a realistic estimate of first-year expenses, backed by the building’s actual operating history.
Whichever you choose, negotiate the details:
- a base year that is the first full calendar year of occupancy
- a 95% gross-up applied only to variable costs
- a reset of the tax base if the base year was reduced under Proposition 8
- exclusion of capital items and a cap on controllable expenses
- audit rights and a billing sunset, commonly two years after year end, which law firm Herrick, Feinstein also recommends
Put these points in your letter of intent so they do not get lost in the lease draft, and have your attorney review the final language.
How do rent escalations interact with a base year?
In a gross lease, annual rent bumps apply to the whole rent, including the expense portion built into it. If you also pay increases over a base year, you cover rising costs twice, though only modestly. That is a fair point to raise when you negotiate the escalation rate. Our guide to the rent escalation clause covers fixed bumps and CPI adjustments.
Worked example: a 6,000 SF unit in a Bakersfield industrial park
A tenant leases 6,000 SF on a modified gross lease. The landlord offers either a 2026 base year or a fixed $2.25 per SF expense stop based on last year’s costs. Actual 2026 expenses come in at $2.40 per SF and rise to $2.52 in 2027. In 2028 the park sells, taxes are reassessed under Proposition 13 and expenses jump to $2.90. The pass-through is the per-SF increase over the threshold multiplied by the tenant’s 6,000 SF. All figures are illustrative, not Kern County data.
Over three years, the expense stop costs the tenant $6,420 against $3,720 for the base year, a $2,700 difference driven entirely by where the threshold started. The 2028 sale hits both structures equally.
| Year | Actual expenses per SF | With 2026 base year ($2.40) | With $2.25 expense stop |
|---|---|---|---|
| 2026 | $2.40 | $0 | $900 |
| 2027 | $2.52 | $720 | $1,620 |
| 2028 (after sale) | $2.90 | $3,000 | $3,900 |
| Three-year total | $3,720 | $6,420 |
Frequently asked questions
Is a base year or an expense stop better for tenants?
A base year is usually better because the threshold tracks what the building really costs. A fixed stop is only as good as the number written into the lease, and the building’s expense history is the best test of that figure.
What happens to my base year if the building sells?
In California, a sale usually triggers a Proposition 13 reassessment to market value, which can raise property taxes sharply. Most leases treat the higher tax as an increase you share. Some tenants negotiate protection, such as excluding reassessment increases for the initial term or a set number of years.
What is a gross-up and why does it matter for a base year?
A gross-up restates variable costs, such as utilities and janitorial, as if the building were at a set occupancy, often 95%. Without it, a half-empty building shows low costs in the base year and your charges jump as it fills. Taxes and insurance generally should not be grossed up.
Does the base year reset when I renew my lease?
Often it does, because landlords want renewal rent to reflect current costs. That is not automatically bad, since new rent then includes current expenses and increases start from a fresh base. The key is to negotiate rent and base year together so you are not paying market rent against an old, low base. See our lease renewal guide for timing.
What does industrial gross mean in a California lease?
It usually means the tenant pays some, but not all, operating costs. Under the AIR multi-tenant gross form common in California, the tenant pays common area costs in full plus increases in property taxes and insurance above a base amount. It sits closer to NNN than the word gross suggests.
Can a base year lease pass through capital costs?
It can if the lease allows it, which is why the definition of operating expenses matters as much as the base. Tenants usually negotiate to exclude capital replacements or to allow them only when spread over the item’s useful life. Without that limit, one paving or roof project can create a large increase in a single year.
Weighing a gross or modified gross lease in Bakersfield or elsewhere in Kern County? Call Kern CRE at 661-885-6949 or contact us and we will help you test the base year or stop against the building’s real expense history before you sign. Get Kern County CRE news monthly: subscribe to the Kern CRE report.
Sources
- AIR CRE, Standard Multi-Tenant Office Lease – Gross (OFG-21.10), AIR CRE, November 2017.
- AIR CRE, Standard Industrial/Commercial Multi-Tenant Lease – Gross (MTG-24.10), AIR CRE, November 2017.
- AIR CRE, Standard Industrial/Commercial Multi-Tenant Lease – Net (MTN-26.10), AIR CRE, November 2017.
- AIR CRE, List of Contracts (form descriptions), AIR CRE.
- PropertyMetrics (citing CCIM Institute), How Does an Expense Stop Work?, January 2023.
- A.CRE (Adventures in CRE), Expense Stop, Glossary of CRE Terms.
- Herrick, Feinstein (via Law360), A Tenant’s Guide To Operating Expense Escalations, February 2013.
- Holland & Hart, Gross-Up Provisions in Commercial Leases, Holland & Hart, undated.
- California State Board of Equalization, Decline in Value (Proposition 8).
- California State Board of Equalization, California Property Tax: An Overview (Publication 29), March 2025.
- Cushman & Wakefield, U.S. Office MarketBeat Q2 2026, Q2 2026.
About this article
Kern CRE prepared this article with help from AI research and writing tools. An editor reviewed the draft, checked its facts against the sources linked above and edited it for accuracy and clarity. It is general information, not legal, tax, investment or financial advice; talk with a qualified professional about your situation.