Pro-Rata Share Explained: What Bookkeepers and Controllers Need to Know
The reconciliation statement for a 10-person dental practice arrived showing total CAM pool expenses of $612,400 for the year. The practice's share, per the statement, came in at $24,496. The bookkeeper was about to post the resulting $7,800 true-up against the estimates already paid. For more context, see CAM red flags accounting firms track.
One question was missing from the workflow: what is the pro-rata share, and is the share on the bill the same as the share in the lease?
The lease, signed in 2019, said 4.0 percent. The reconciliation used 4.5 percent. The difference is $3,062 on this single year. The dental practice had been overpaying for two years, and nobody on the accounting side had ever opened the lease to check.
The pro-rata share is the most leveraged number in any CAM reconciliation. It is also the easiest one to miss, because it appears on the statement looking final. This article explains what the share is, how it is calculated, and what to do when the number does not line up.
Pro-Rata Share: The percentage of a commercial building''s operating expenses allocated to an individual tenant, calculated as the tenant''s rentable square footage divided by the building''s total rentable square footage. The pro-rata share is multiplied against the expense pool to compute the tenant''s share of CAM, taxes, insurance, and other pass-through costs. The share is set in the lease and may need to be updated when the building is expanded, retenanted, or remeasured.
How the math actually works
The calculation has two inputs:
- Numerator: tenant rentable square footage
- Denominator: building (or center) rentable square footage
A 2,000 square foot tenant in a 50,000 square foot office building has a 4.0 percent pro-rata share. If the building's annual operating expenses are $1,200,000, the tenant's share is $48,000. The reconciliation should reflect $48,000 minus whatever the tenant paid in monthly estimates.
It sounds simple. Three things complicate it in practice:
- The square footage figures are not always documented consistently
- The denominator changes when the building changes
- Some leases use a "majority occupied" or "gross-up" adjustment that effectively modifies the math
Each of those creates a path to an incorrect bill.
Where the share gets wrong
The denominator is stale. The building is 50,000 square feet on the day the lease is signed. Three years later the landlord adds a 10,000 square foot pad to the back of the lot. The total denominator is now 60,000. Existing tenants' shares should drop proportionally. They almost never do, because the lease abstract used to administer the rent roll keeps the original 50,000 figure forever.
The numerator is a load factor. Office leases often state the rentable square footage as the usable square footage plus an allocated share of common areas (lobbies, hallways, restrooms). If the load factor is recalculated when a new tenant moves in or moves out, individual tenant rentable figures can shift. The lease number is usable plus loaded common area, which creates room for arithmetic errors that compound across the rent roll.
The share is denominated in dollars instead of square feet. Some leases set the share by negotiated percentage rather than by square footage. A tenant with leverage at signing can negotiate a 4.0 percent share when the strict math would have been 4.5 percent. That negotiated figure is the lease share, and any reconciliation using a different number is wrong.
Vacancy adjustments are misapplied. When the building has vacancy, certain expenses (variable costs that scale with occupancy, like utilities and janitorial) should be grossed up to what they would have been at full occupancy. Other expenses (fixed costs like property taxes) should not. Misapplying gross-up to fixed costs over-allocates to occupied tenants.
How to verify the share at close
A practical 10-minute check the bookkeeper or controller can run when the reconciliation arrives:
Step 1. Pull the lease and find the basic lease information section. Locate the tenant's pro-rata share. Write down both the percentage and the square footage figures (numerator and denominator) if both are stated.
Step 2. Find the pro-rata share on the reconciliation statement. It is usually labeled "Tenant Share" or "Proportionate Share" and shown as a percentage to one or two decimal places.
Step 3. Compare. If the percentages match, move to the expense pool review. If they do not match, stop posting and escalate.
Step 4. If the share is not stated on the reconciliation, request it in writing. The landlord is required to support pass-through charges with the underlying calculation in nearly every well-drafted lease.
Even when the percentages match, one more check helps: take the total expense pool from the reconciliation, multiply by the pro-rata share, and confirm it ties to the tenant's allocated total on the bill. The arithmetic should reconcile to the dollar. When it does not, there is usually a hidden adjustment somewhere on the statement worth reading.
The retenanting trap
The most common silent error in pro-rata share is not a calculation mistake. It is a denominator that should have changed and did not.
A 3-location retailer signs a lease in a power center in 2018 with a 6.2 percent share based on a 75,000 square foot center. In 2021 the landlord adds a 25,000 square foot anchor box to the back of the property. The center is now 100,000 square feet. The retailer's correct share, based on its unchanged 4,650 square feet, is 4.65 percent.
The reconciliations from 2021 forward should reflect the new denominator. In about half the cases I have seen run through CAMAudit, they do not. The landlord's property accounting system rolls forward last year's percentages, and the new anchor's contribution to the denominator never makes it into existing tenants' calculations. The result is a 1.55 percent overcharge that compounds across the entire pass-through pool every year.
For a 3-location retailer paying $400,000 a year in pass-throughs across the portfolio, a 1.55 percentage point error is roughly $6,200 per year per location. Multiply by three locations and three years and the cumulative exposure is in the $50,000 to $60,000 range, sitting quietly in the books as Occupancy Expense.
"Pro-rata share denominator errors are the highest-recovery findings I see when running reconciliation samples. The landlord''s system rolls forward the original percentage, the tenant''s system trusts the bill, and the gap quietly persists for years. The fix takes one email to the landlord requesting a building rentable square footage update." — CAMAudit field notes after testing reconciliation samples from published audit cases
What this means for the chart of accounts
Pro-rata share verification is easier when the chart of accounts is structured to support it. A few setup choices help:
- Separate accounts for base rent, CAM, taxes, and insurance pass-throughs (rather than one bundled rent account)
- A class or location dimension for multi-location clients so each lease's pass-throughs are visible independently
- A memo or custom field on the recurring rent invoice that captures the lease's pro-rata share
- An annual reminder in the close calendar to verify the share against the lease for every commercial tenant client
That last one is the highest-leverage habit. The share rarely changes year to year for stable buildings, but when it does change, it changes silently. A documented annual check is the only systematic way to catch the change without running a full audit.
When to escalate past bookkeeping
Spot the red flag, preserve the document, escalate when it moves beyond bookkeeping review. The pro-rata share question moves out of bookkeeping scope when:
- The reconciliation share does not match the lease share
- The building has been expanded, retenanted, or remeasured during the lease term
- Multiple years of reconciliations have used the same percentage despite obvious building changes
- The reconciliation does not show the underlying square footage figures
At that point the issue is lease compliance and document review, not coding. The right step is to flag the file for a controller-level review or refer it to a CAM specialist who can request the supporting documentation and pursue the recovery.
The dental practice in the opening example recovered $6,124 across two years once the share was corrected. The bookkeeper found the discrepancy in 12 minutes by opening the lease before posting the bill. That is the workflow that turns transaction processing into client value.