You get the year-end CAM reconciliation and the number stops you cold. Your CAM charges jumped $4,800 over the prior year. The building looks exactly the same. You did not expand your space. Nothing changed on your end.
What changed: the anchor tenant left.
This is one of the most common, and least explained, CAM spikes in retail leases. When a department store or big-box anchor vacates, the in-line tenants who share the building often absorb a larger percentage of the total CAM pool, sometimes immediately, sometimes in the next reconciliation cycle. It is not accidental. It is how the math works. And in some cases, it is also how landlords use gross-up clauses to add expenses to the pool that never actually occurred.
How pro-rata share math changes when an anchor leaves
Your CAM charge is your pro-rata share of the total CAM pool: your square footage divided by the total rentable square footage of the building, multiplied by the total CAM expenses.
Most leases exclude anchor tenants from the CAM pool entirely. Anchors often negotiate separate self-maintenance agreements where they cover their own space and surrounding common areas, so they get removed from the shared denominator. That is standard. Here is what it means for your bill.
Say the building is 100,000 square feet. The anchor occupies 30,000 square feet and is excluded from the CAM denominator. You occupy 5,000 square feet. The effective denominator is 70,000 square feet (100,000 minus the anchor's 30,000).
Your pro-rata share: 5,000 ÷ 70,000 = 7.14%
Now the anchor leaves. The landlord re-leases that space, or more likely, it sits vacant. If the new tenant is not yet occupying the space, or if the landlord recalculates the denominator without the anchor's square footage because they are no longer a party to the lease, your denominator shrinks.
If the denominator drops to 50,000 square feet (the remaining occupied tenants), your share becomes:
5,000 ÷ 50,000 = 10%
That is a 40% increase in your pro-rata share with no change to your physical space. On a $300,000 CAM pool, that shift moves your annual bill from $21,420 to $30,000, a difference of $8,580 per year.
The question your lease has to answer: what is the denominator supposed to be? Most well-drafted leases define it as the total rentable area of the building, not the total occupied area. If your lease uses full building square footage, the anchor's departure should not change your share at all. If it uses occupied square footage, every vacancy shrinks the pool and your share grows.
Pull your lease and look at how it defines "rentable area" and "pro-rata share." Those two definitions tell you whether the landlord's calculation is authorized or not.
The gross-up exploitation risk
Pro-rata share is only part of the problem. The other issue is what happens to the expenses themselves.
Many commercial leases include a gross-up clause. The idea behind it is not unreasonable: if the building is partly vacant, some variable expenses (cleaning, HVAC, utilities) are lower than they would be at full occupancy. To keep tenants from getting an unearned cost break from a vacancy they did not cause, landlords can gross up those variable expenses to what they would have been at 95% occupancy.
That logic has a limit. Here is where it breaks down.
The anchor occupied 30,000 square feet of a 100,000 square foot building, 30% of the total space. The landlord can now apply the gross-up clause to inflate variable expenses by a factor that restores the total to 95% occupancy levels.
If actual HVAC and cleaning costs for the building were $80,000 at 70% occupancy, the landlord can gross up that figure to approximately $108,571 (80,000 ÷ 0.70 × 0.95) to simulate 95% occupancy. That is $28,571 in expenses that never actually occurred, added to the CAM pool, then distributed across your share.
Two things to check:
First, which expense lines were grossed up. Variable expenses like utilities, janitorial, and parking lot maintenance are fair gross-up candidates. Fixed expenses like property management fees, insurance premiums, and security contracts do not change with occupancy and should not be grossed up. If the landlord grossed up fixed costs, that is an overcharge.
Second, whether the gross-up exceeded your lease cap. Many leases cap gross-up at 95% of the occupied area, not 100% of the building. If the calculation pushed expenses above that cap, the excess is billable to you without authorization.
What your lease should say about anchor departures
A co-tenancy clause is your main protection here. Not every retail lease has one, and the ones that do vary a lot in what they actually deliver.
When a named anchor leaves, a co-tenancy clause typically gives you at least one of these:
A rent reduction, sometimes called "fallback rent," that takes effect while the anchor space sits vacant or until a comparable replacement opens. A termination right, usually triggered if the space stays empty for 6 to 18 months, letting you exit the lease without penalty. And in some leases, a CAM contribution cap that limits your exposure to what you would have paid if the anchor were still in occupancy.
If your lease has a co-tenancy clause, two things matter: whether this specific tenant's departure actually triggered it (some clauses name specific anchors, or require a minimum number of named tenants to remain), and whether you sent written notice within the required window. Most co-tenancy clauses require written notice within 30 to 90 days of the triggering event. Miss that window and the right expires.
If your lease does not have a co-tenancy clause, your protection comes from the denominator and gross-up language only.
How to audit your reconciliation after an anchor departure
A higher CAM bill is not automatically an overcharge. The math might be legitimately higher. You cannot tell without checking the inputs, and that means getting the right documents.
Start with the prior-year reconciliation. Compare the denominators side by side: what square footage did the landlord use as the divisor last year versus this year? If it changed, send a written request asking which lease provision authorizes the change. Get it in writing.
Then request the gross-up calculation backup. The landlord should be able to show you which expense lines were grossed up, the actual amounts, the percentage applied, and the resulting figures. If they cannot produce this on request, the gross-up may not survive a dispute.
Go through each grossed-up line and categorize it. Variable expenses (HVAC, utilities, janitorial, trash removal, parking lot maintenance) are legitimate candidates. Fixed expenses (management fees, insurance premiums, property taxes, administrative fees) are not. Flag any fixed-cost line that was inflated.
Then verify the cap. If your lease says gross-up cannot push expenses above what they would be at 95% occupancy, calculate that figure and compare it to what was billed.
Finally, if you have a co-tenancy clause, check whether you received any rent adjustment and whether the CAM exposure was capped as the clause specifies.
When you upload your lease and reconciliation to CAMAudit, the tool runs the pro-rata share and gross-up checks automatically. It flags denominator inconsistencies, identifies fixed expenses that were incorrectly grossed up, and checks whether the gross-up percentage exceeds your lease cap.
What to do if you find an overcharge
If the denominator changed without lease authorization, or if fixed expenses were grossed up, you have a dispute. It starts with a written notice to your landlord, not a phone call.
Most commercial leases include an audit rights clause in the CAM or operating expenses section. That clause gives you the right to request supporting documentation and, in most cases, to formally dispute the calculation within a defined window. Common windows run 60 to 365 days from the date the reconciliation was delivered. Outside that window, you may be barred from disputing the current year's charges entirely.
A workable sequence:
On day one, request the reconciliation backup in writing. Ask for the rent roll, the expense ledger, and the gross-up calculation. By day 30, review the backup against your lease terms and identify the specific line items in dispute. By day 45, send a written dispute citing the exact lease provision, the incorrect calculation, and the dollar amount in dispute. Do not dispute the whole bill, just the specific line items where the math is wrong. If you have not heard back by day 60, follow up. If the landlord refuses to produce backup documentation, that is when an attorney earns their fee.
The strongest disputes cite the exact lease provision, show the correct calculation alongside the landlord's, and state the dollar difference clearly. Vague complaints about a high bill rarely move anyone. Specific math does.
If the anchor left mid-lease and prior reconciliations used the same incorrect denominator or the same gross-up methodology, check your lease's audit lookback window. Many leases allow you to audit up to three prior years. The same math error running for three years produces three times the overcharge.
Most landlords recalculate correctly after an anchor leaves. Some do not. The only way to know which situation you are in is to check the denominator, check the gross-up methodology, and compare both to what your lease actually authorizes.
Upload your lease and CAM reconciliation to run a CAMAudit scan. The pro-rata share and gross-up checks are part of every scan, and you will have the results in minutes.