Your Pro-Rata Share: The Most Common CAM Overcharge
Your CAM share is a fraction: your square footage divided by the building's total square footage. If the denominator — the building total — is understated, or if your RSF is overstated, that single wrong fraction gets multiplied against every CAM dollar the landlord spends. You don't overpay on one line item; you overpay on the whole reconciliation, every year, for the life of the lease. Tango Analytics (2023) found roughly 40% of CAM reconciliations contain material errors, and a mis-set pro-rata share is one of the quietest ways that happens.
How is my CAM pro-rata share calculated?
Your pro-rata share is your space's Rentable Square Footage (RSF) divided by the building's total rentable square footage. The numerator is your suite; the denominator is the whole building (or the whole shopping center). If you lease 5,000 RSF in a 100,000 RSF building, your share is 5% — so you pay 5% of every CAM expense. The math is simple, which is exactly why an error in either number hides in plain sight.
Why is the denominator the silent lever?
The denominator quietly controls your entire bill because shrinking it raises everyone's share. If the landlord uses 90,000 RSF instead of the true 100,000 RSF as the building total, your 5,000 RSF suite jumps from a 5% share to a 5.56% share — an 11% increase on every CAM dollar, with no change to your actual space. Tenants scrutinize their own square footage but rarely question the building total, and that's the number doing the most damage. You can estimate the dollars at stake from an overstated denominator with our free calculator.
What's the difference between RSF and USF, and what is load factor?
Usable Square Footage (USF) is the space you can actually occupy; Rentable Square Footage (RSF) is your USF plus a share of common areas like lobbies, corridors, and restrooms. The ratio between them is the load factor (also called the loss factor or add-on factor): RSF ÷ USF. A 15% load factor turns 5,000 USF into 5,750 RSF. If the landlord applies an inflated load factor to your numerator, your RSF is overstated and your share rises — so it's worth knowing both numbers and the ratio between them.
What is "denominator contraction" and why is it a red flag?
Denominator contraction is when the building's total square footage shrinks from one year to the next without a real-world reason. Buildings don't usually get smaller. If last year's reconciliation used 100,000 RSF as the building total and this year's uses 95,000 RSF, your share went up even though nothing about your space changed. Comparing the denominator across consecutive reconciliations is one of the fastest informational checks you can run.
Can the landlord's denominator be cross-checked against public data?
Yes — the building's size often appears in independent public sources you can compare against the number on your statement. County assessor and tax records list a building's gross area; if the landlord is a public REIT, its size figures may appear in SEC filings; and BOMA (Building Owners and Managers Association) publishes standardized measurement methods and benchmark ranges. When the denominator on your reconciliation doesn't line up with what public data shows, that gap is worth a closer look. This is ReCAM's core function: we cross-check the landlord's denominator against independent public data rather than taking the stated number at face value.
What is my right-to-review-records window?
Most commercial leases give you a time-limited window — often called "audit rights" — to request the landlord's supporting documentation after a reconciliation is issued. That's when you can ask for the calculation behind the building total and your RSF. The window is short and often expires, so confirm your deadline before it closes; missing it can mean losing the right to question the numbers for that year.
The principle to remember: your CAM bill is only as accurate as the fraction behind it. Verify both the numerator (your RSF) and the denominator (the building total) — a wrong fraction overcharges you on everything.
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Informational only; not legal advice and not an audit or attest service. ReCAM is not a CPA firm and these services are not regulated by the Texas State Board of Public Accountancy. © ReCAM Technologies LLC.