What is a base year in a commercial lease?

The base year is a reference year used to establish the baseline for operating expenses. The landlord absorbs expenses up to the base year amount, and the tenant pays only the increase above that amount in subsequent years. It is most common in full-service gross and modified gross leases.

Why does base year occupancy matter?

If the building was only 60% occupied during the base year, actual operating expenses were lower than normal. Without a gross-up provision, the base year figure is artificially low, meaning tenants pay higher overages in subsequent years even if real costs have not changed much.

How does CAMAudit verify base year figures?

CAMAudit's Rule 7 (Base Year Error) compares the base year expense figure used in your reconciliation against the actual base year documentation. It checks for occupancy adjustments, assessment timing, and mathematical accuracy to ensure your baseline is correct.

Base Year Stop Clause

Last updated: April 2026

By Angel Campa, Founder

A low base year inflates every future year's expense pass-through, potentially costing tenants $1-3 per square foot annually over the full lease term.

What Is a Base Year Stop Clause?

A base year stop clause sets a benchmark year for operating expenses. The tenant pays operating expenses only to the extent they exceed the base year amount (the "stop"). This means the landlord absorbs costs up to the base year level and the tenant pays the overage. The base year is typically the first year of the lease term.

Why This Clause Matters for CAM Audits

Base year clauses directly determine how much of the operating expense increase a tenant actually pays. If the base year amount is artificially low (due to renovations, partial occupancy, or landlord manipulation), tenants end up paying more in subsequent years. Verifying the accuracy of base year figures is essential to ensuring fair pass-throughs over the life of the lease.

Sample Lease Language

“Tenant's obligation to pay Operating Expenses shall be limited to the amount by which actual Operating Expenses for each calendar year during the Lease Term exceed the Operating Expenses incurred during the Base Year. The "Base Year" shall be calendar year 2026. Base Year Operating Expenses shall be calculated on an actual, fully-occupied, fully-assessed basis. If the Building is less than ninety-five percent (95%) occupied during the Base Year, Operating Expenses shall be grossed up to reflect ninety-five percent (95%) occupancy.”

This is illustrative language only. Your actual lease language controls your rights.

Red Flags to Watch

⚠Base year falls during a period of unusually low expenses (major renovation, partial occupancy, tax abatement)
⚠No provision to gross up base year expenses if the building was not fully occupied
⚠Landlord can adjust the base year retroactively for any reason
⚠Base year expenses are "estimated" rather than actual
⚠No right to audit or verify the base year expense figure

Free scan · No account required

Was Your Base Year Set Fairly?

Upload two PDFs. 14 detection rules. Under 15 minutes. Free.

Find My Overcharges See a sample report first

Negotiation Tips

✓Require base year expenses to be calculated on a fully-occupied, fully-assessed basis to prevent artificially low baselines
✓Negotiate the right to audit and challenge the base year figure within 12 months of receiving it
✓If the base year falls during construction or renovation, negotiate a normalized base year that reflects typical operating conditions
✓Include language prohibiting retroactive adjustments to the base year amount

Key Data

$1-3/sqft
An artificially low base year can increase a tenant's annual expense pass-through by an estimated $1 to $3 per square foot [industry estimate]
Source: Commercial Lease Audit Reports (2024)

Explore Other Lease Clauses

Audit Rights Clause CAM Cap Clause CAM Exclusion Clause Gross-Up Provision Management Fee Clause Pro-Rata Share Definition Clause Controllable vs Non-Controllable Expense Clause Capital Expenditure Exclusion Clause Self-Help Remedy Clause Reconciliation Statement Deadline Clause Co-Tenancy Clause Operating Expense Definition Clause

Free scan · No account required

Was Your Base Year Set Fairly?

Upload two PDFs. 14 detection rules. Under 15 minutes. Free.

Find My Overcharges See a sample report first

Related Guides

Lease LanguageOverview

Base Year and Expense Stop: How They Work and Get Manipulated

CAM ReconciliationGuide

Expense Stop vs. Base Year: Which Costs You More?

Lease LanguageOverview

Modified Gross Lease Explained: CAM Exposure, Cost Split, and Hidden Overcharges

Lease LanguageOverview

Modified Gross vs. NNN Lease: Side-by-Side Comparison [2026]

Explore Related Resources

CAM Line ItemProperty Taxes (Pro-Rata)CAM Line ItemCommon Area Insurance Lease TypeFull Service Gross Lease (FSG)Lease TypeModified Gross Lease Detection RuleBase Year Error Detection RuleGross-Up Violation

Next Best Step

Turn this risk into an audit

Walk through the full audit steps before you upload your lease and CAM statement.

What is a CAM audit?

Review the audit process before you upload your lease and reconciliation.

See a sample report

See the output and proof structure before you commit.

Start Free Audit

Run the free audit when you want documented findings.

Ready to skip the reading and document the overcharge directly?

Find My Overcharges

Related Resources

Detection RuleBase Year Error Detection RuleGross-Up Violation Detection RuleEstimated Payment True-Up Error CAM Line ItemProperty Taxes (Pro-Rata)CAM Line ItemCommon Area Insurance Lease TypeFull Service Gross Lease (FSG)

Frequently asked questions

Need to extract lease terms before your audit?

A CAM audit is only as accurate as your lease data. lextract.io extracts 126 structured fields from any commercial lease PDF: CAM definitions, pro-rata share, caps, base year, and audit rights. So you have the exact terms your landlord is supposed to follow.

Go to lextract.io

This page provides general educational information. It is not legal advice and may not reflect the most current law in your state. Consult a licensed attorney for advice specific to your situation.