A wrong base year costs you money every single year of your lease, not just one. Here's how base year errors compound over time and what to do about them.
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Find My OverchargesSee a sample report firstA base year error is one of the highest-value overcharge types in a long-term commercial lease, not because the first year's impact is large, but because the error repeats. Every year you pay based on a wrong baseline, you overpay by the same amount. Over a 10-year lease, even a modest base year error can add up to six figures.
In a base year lease, you only owe increases above the established baseline. If that baseline is artificially low, either because it was set at a year with below-normal occupancy and not grossed up, or because the wrong year was used entirely, you pay "increases" that are not actual increases at all. They are just the gap between the wrong baseline and normal operating costs.
The base year structure is more common in office leases than in retail NNN leases, though it appears in both. Instead of paying all operating costs from the first dollar, you pay only the amount by which costs in a given year exceed a defined baseline. The baseline is typically set at the first full year of your tenancy, or at a year specified in the lease.
For example: base year operating costs are set at $22 per square foot. In year three, costs are $25 per square foot. You pay the $3 per square foot excess. In year five, costs are $27 per square foot. You pay the $5 excess.
If the base year is set at $19 per square foot instead of $22, you pay $6 in year three and $8 in year five. That is $3 per square foot per year in excess charges that should not exist, compounding across the entire lease term.
The most common type of base year error is not an outright wrong figure, it is a base year that was set at a year when the building had below-stabilized occupancy, without adjusting (grossing up) the variable costs to reflect what they would have been at normal occupancy.
Variable operating expenses like cleaning, landscaping, and building utilities do not increase linearly with occupancy, but they do increase meaningfully. A building that was 65% occupied in the base year had lower cleaning costs, lower trash removal costs, and lower HVAC costs than it would at 90% occupancy. If the base year records those actual low-occupancy costs without adjustment, you are compared against an artificially low baseline in every subsequent year when the building fills up, even if costs per square foot stayed flat.
The practitioner paper "Negotiating Commercial Real Estate Acquisitions and Leases" (published by sbaustinlaw.com) explains this mechanism with explicit numbers: the gross-up provision adjusts variable costs upward in the base year to a stabilized occupancy level, typically 90% or 95%, before locking in the baseline. Without that adjustment, the base year represents a below-market cost level that sets the wrong reference point for every subsequent year.
BOMA's Green Lease Guide confirms that 95% is the most common gross-up target used in the industry, though 90% also appears. Some leases gross up to 100%, which eliminates the problem of residual vacancy risk entirely but creates a different calculation issue if the building later exceeds 100% (theoretically impossible but practically relevant for multi-building campus properties).
A publicly available modified gross office lease filed with the SEC uses a 95% occupancy trigger as a standard reference point in its gross-up provision, illustrating that this is a market-norm drafting expectation, not a tenant-specific negotiated protection.
A separate error is using the wrong year entirely. Your lease specifies Year 1 (the first full year of occupancy) as the base year. The landlord calculates the base using Year 2 figures, or pre-occupancy construction costs, or costs from the year before your lease commenced.
This type of error is most common after long tenancies, property sales, or management changes where the original base year documentation was not transferred with the lease file. A new property manager may use the oldest year in the accounting system as the base, which may not match the lease's definition.
In Samuel Walton d/b/a Gailrach Realty Co. v. Eastern Analytical Labs, Inc., 246 A.D.2d 532 (N.Y. App. Div. 1998), the court enforced the lease requirement that the landlord submit annual computation statements as a condition precedent to collecting additional rent based on operating expense escalations. Because the landlord failed to provide those statements for several years, the tenant was held not liable for the claimed escalations. The procedural right to receive a documented statement is worth asserting if you have not been getting one.
Let's say the base year was set at $18 per square foot, when the correct grossed-up figure should have been $21 per square foot. The error is $3 per square foot annually. You occupy 4,000 square feet.
Annual excess charge attributable to the base year error: $3 × 4,000 = $12,000 per year
Total over 10 years at flat costs: $12,000 × 10 = $120,000
If operating costs actually grew over the decade, the cumulative overcharge is higher still, because the wrong baseline inflates not just current-year charges but the growth measured above that baseline.
For a real-world sense of scale: in Kramer Levin Naftalis & Frankel, LLP v. Metropolitan 919 3rd Avenue, LLC, 2004 NY Slip Op 24510 (N.Y. Sup. Ct. 2004), the tenant sought a rent credit based on a dispute about how base-year costs were compared against subsequent years' operating expenses and taxes. The court's analysis focused heavily on limitations periods and when claims accrued, which is a reminder that even large, well-founded base year claims can be extinguished by procedural deadlines if not raised promptly.
Find the base year definition in your lease. Confirm the specific year and whether costs are defined as actual costs, grossed-up costs, or estimated costs.
Request the actual operating expense reconciliation from the base year (or the base year schedule if a reconciliation was not prepared). This should show the line-item costs that were used to set the baseline.
Check the building's occupancy during the base year. If the building was below the gross-up threshold (typically 90-95%), confirm whether variable costs were adjusted upward before the baseline was locked in.
Identify variable versus fixed costs. Gross-up applies to variable costs (cleaning, landscaping, utilities correlated with occupancy) but not fixed costs (base property taxes, insurance premiums). The gross-up calculation should only touch the variable portion.
Compare the baseline in your current reconciliation to the documented base year costs. A material discrepancy, more than a few percent, warrants a written request for documentation and explanation.
Yes, within the applicable audit window and statute of limitations. Most states allow 3-6 years for written contract claims. Your lease's audit rights clause may impose a shorter window for each year's reconciliation, often 60-90 days from receipt. If you have missed prior-year windows, you may still have claims for years within the limitations period. The base year error itself never expires until the lease expires; it is a structural error that affects every year, so raising it at any point during the lease is appropriate.
The burden of establishing the correct base year cost is typically the landlord's. If the landlord cannot produce documentation of the base year costs, that is a problem with the landlord's records, not your ability to dispute the figure. Request the documentation in writing. If the landlord cannot provide it, the undocumented baseline is subject to reasonable dispute.
A base year lease anchors the baseline to actual costs in a specific historical year. An expense stop anchors the baseline to a fixed dollar amount, regardless of what costs actually were in any year. Both structures work the same way, you pay increases above the baseline, but a fixed expense stop is not subject to the gross-up problem because it is not derived from historical occupancy-dependent costs.
Sometimes. If the base year was inflated (recording higher-than-actual costs), the pass-through in subsequent years would be lower than it should be, the landlord set the baseline too high and you would pay less in excess charges. Base year inflation is less common than deflation in practice, because the financial incentive runs the other way, but it does occur when a landlord is poorly positioned or inexperienced.
Gross-up target disputes (whether to use 90% or 95% or 100%) are ultimately governed by the lease language. If the lease specifies a target, that target controls. If the lease requires gross-up without specifying a target, 95% is the most common market practice based on BOMA and published industry guidance, and arguing for 95% is defensible.
CAMAudit compares the base year figure in the reconciliation against the lease's base year definition and any documentation you upload for the base year period. The system also checks whether the building's occupancy history suggests a gross-up should have been applied and flags the discrepancy with a dollar estimate of the annual impact.
See also: The CAM Overcharge Detection Playbook, all 12 detection rules with worked examples.
Related: Base year adjustment in CAM leases | CAM cap violations: cumulative versus compounded calculations | How to audit your CAM statement step by step | CAM Overcharge Recovery Guide