Lease Commencement Date: Definition, CAM Impact, and Disputes
Most tenants know when they signed their lease. Fewer know exactly when their lease commenced, which is a different date, and a date that carries significant financial consequences. The lease commencement date is the anchor for rent obligations, CAM obligations, the base year definition, and the audit window. Getting it wrong, or accepting a landlord's interpretation that does not match the lease language, can cost your client money.
What the lease commencement date is
The lease commencement date is the date from which rent and CAM obligations begin running. It is usually defined explicitly in the lease, either as a fixed calendar date or as a date triggered by an event (delivery of the space, substantial completion of landlord's work, or a fixed period after the lease execution date).
Three dates are often confused with each other:
Execution date: The date the lease was signed by both parties. This starts the contractual relationship but does not start most financial obligations.
Possession date: The date the landlord delivers physical access to the space. This may come before the commencement date (to allow the tenant to begin its buildout) or it may coincide with commencement.
Commencement date: The date from which base rent and CAM obligations begin accruing under the lease terms.
In a straightforward deal, all three happen close together. In a deal involving a significant buildout, tenant improvement allowance disbursement, or phased delivery, the gaps between these dates can span months, and each gap carries specific financial implications.
How CAM is handled during the pre-commencement period
Most commercial leases require CAM payment from the possession date even if base rent is abated during a buildout or fixturing period. The logic the landlord applies is that the tenant is occupying and using the building's common areas (parking, lobbies, HVAC, security) even before they open for business, and those costs do not pause because the tenant has not yet started paying rent.
This is a significant and frequently overlooked obligation. If a client's lease grants four months of rent-free occupancy for buildout and the annual CAM estimate is $48,000, the client may still owe $16,000 in CAM during those four months, even while paying no base rent. The lease typically spells this out in the CAM definition or in a separate pre-opening obligations section, but it is easy to miss in a long lease document.
The practical implication: when you review a client's first-year CAM reconciliation, the year may include partial-year CAM from a pre-commencement possession period that predates what looks like "year one." Price that pre-commencement period into the client's cost model before they sign.
The relationship between a client's commencement date and base year directly determines their gross-up exposure in years two through ten.
The base year and its relationship to commencement
For office leases and some retail leases structured as modified gross or base year leases, the base year is set relative to commencement. The base year is the landlord's actual operating expenses for a defined period, typically the calendar year of commencement or the first 12 months after commencement. The tenant pays the excess of actual CAM over the base year amount in subsequent years.
If a client's lease commences on October 1, 2025, a calendar-year base definition means the base is the landlord's 2025 operating expenses. But the client only occupied the space for the last quarter of 2025. If the base year is calculated on full-year 2025 expenses, the client gets the benefit of a full year of costs against which future increases are measured, which is favorable. If the lease requires the base to be annualized from partial-year occupancy, the calculation matters enormously. A landlord who annualizes using a low-expense quarter produces a different base than one who uses the full calendar year.
The gross-up provision interacts directly with this. In years where the building is under-occupied, operating expenses may be artificially low because some costs scale with occupancy. If the base year is set when the building is 70% occupied and the lease allows gross-up to 95%, the grossed-up base year expenses will be higher than actual, reducing the spread in future years and lowering the client's escalation exposure. But the exact calculation depends on when the client's commencement falls relative to the building's occupancy levels that year.
Disputes over the commencement date
Late delivery
When the landlord does not deliver the space by the contractually agreed delivery date, the commencement date may shift. Leases typically handle this one of two ways: the commencement date is pushed out by the same number of days the delivery was delayed, preserving the tenant's rent-free period and buildout schedule; or the commencement date stays fixed but the rent-free period is extended by the delay period.
The two approaches produce the same rent outcome but different CAM outcomes. If the commencement date shifts, the base year definition may move to the next calendar year. If the date stays fixed but the tenant gets more free-rent days, the base year stays as originally set.
Which approach a client's lease uses, and whether the landlord actually applies it correctly, is worth verifying before the first reconciliation arrives.
Substantial completion vs. full completion
Many leases tie commencement to "substantial completion" of landlord's work rather than full completion. Substantial completion typically means the space is usable for its intended purpose even if minor punch-list items remain. Whether the space was substantially complete on a specific date is frequently disputed, especially when the tenant claims they could not open for business due to outstanding work.
Courts and arbitrators apply different tests for substantial completion depending on lease language and jurisdiction, but the core question is always whether the remaining work prevented the tenant from making productive use of the space. A missing floor finish that delays opening is treated differently from missing decorative trim that does not affect operations.
Year-1 proration and CAM exposure
When a lease commences mid-year, the first-year reconciliation creates a partial-year CAM exposure that differs from subsequent years. This proration, if handled incorrectly, can overstate the client's first-year obligation.
Numeric example: a client's lease commences July 1, 2025. Annual CAM is $60,000 per year. First-year CAM for the 6-month period from July 1 through December 31 should be $30,000 (6/12 of the annual amount, applied to actual expenses for those 6 months).
If the landlord's reconciliation uses the full-year operating expenses of $60,000 for 2025 without prorating to the client's actual period of occupancy, the client is being billed $30,000 too much. This exact error appears in CAM audit findings more often than firms might expect. The property management system calculates a pro-rata percentage and applies it to full-year expenses without adjusting for the partial occupancy period.
A related issue: some landlords bill estimated CAM monthly from commencement, then reconcile at year-end. If estimated monthly payments were collected starting July 1 but the reconciliation uses full-year actual expenses without adjusting, the reconciliation balance due will be overstated.
What to have clients document at lease commencement
Documentation at commencement creates the evidentiary record for every dispute that follows. The items worth capturing:
Space condition: Advise the client to walk the space with the landlord's representative and document anything that is not per the lease or the work letter. Photograph every incomplete item. If the landlord claims substantial completion but work is outstanding, the client wants a record of exactly what remained at the date they declared completion.
Meter readings: If the lease includes direct utility billing or sub-metering, read the meters on commencement day. Disputes over utility charges frequently come down to what the starting baseline was.
Square footage verification: If rent and CAM obligations are calculated per square foot, measure or confirm actual usable square footage before commencement, not three years in. Errors in the lease square footage survive undetected for years when no one measures.
Delivery letter: Some leases require the landlord to deliver a written notice confirming the commencement date once they have delivered the space. If the lease requires this notice and the landlord did not deliver one, document the actual date the client received keys or access regardless.
Rent commencement date confirmation: Get written confirmation of when rent and CAM begin. If there is any ambiguity about the free-rent period or the handling of a delayed delivery, put the agreed date in writing before the client starts paying.
These records matter most in years 4 through 7, when a landlord may attempt a retroactive adjustment to first-year CAM that depends on their interpretation of the commencement date. Leases that were not well-documented at signing often produce disputes that are genuinely difficult to resolve because neither party has reliable records.
Frequently Asked Questions
What is a lease commencement date?
The lease commencement date is the date from which rent and CAM obligations begin under the lease. It is often different from the date the lease was signed (execution date) or the date the tenant received physical access to the space (possession date). The commencement date is the anchor for base year calculations, audit windows, and the timeline of all financial obligations under the lease.
When does CAM obligation begin relative to lease commencement?
Most commercial leases require CAM payments from the possession date, which may be earlier than the base rent commencement date. Even during a rent-free buildout or fixturing period, tenants are typically obligated to pay their share of CAM because they are using building common areas. This pre-commencement CAM obligation is often missed and can add up to several months of CAM before the tenant opens for business.
What happens if the landlord delays delivery past the commencement date?
Depending on lease language, a late delivery either shifts the commencement date (pushing all obligations back by the delay period) or keeps the commencement date fixed while extending the rent-free period. The two approaches produce the same rent outcome but different base year and CAM outcomes. The applicable method should be spelled out in the lease, and any agreed adjustment should be confirmed in writing before the first rent payment.
How does lease commencement affect the CAM base year?
The base year is typically set as the calendar year of commencement or the first 12 months of the lease. If the lease commences mid-year, the base year calculation depends on whether the landlord uses actual partial-year expenses or a full-year annualized figure. For tenants in base year leases, a mid-year commencement creates meaningful variability in the base year expense figure, which affects every future escalation calculation for the life of the lease.