A CAM reconciliation is the year-end statement that squares what you collected in monthly operating cost estimates against what the building cost to run. If your leases are net, you owe your tenants one. The disputes it sets off are rarely arguments about whether a cost was reasonable. They are arithmetic done in the wrong order, which is what makes an honest statement look like an overcharge.
Here is the sequence. It holds for office, retail and industrial, and your lease supplies the inputs at every step.
Read the operating cost clause before you open the ledger
The lease is the authority, not your accounting system. Canadian commercial leases usually call this Operating Costs or Additional Rent rather than CAM, and retail leases often split common area maintenance from taxes and insurance into separate recoveries with separate rules. Before anything else, write down five things from the clause: what the pool includes, what it excludes, how proportionate share is defined, whether there is a gross-up, and what caps or base year offsets apply.
Expect those five answers to differ by tenant in any building holding leases from different decades. Reconcile the pool once, then allocate lease by lease.
Lock the denominator first
Proportionate share is a fraction, and the denominator is where the money is. A tenant's numerator is their rentable area, which the lease usually defines by reference to a BOMA measurement standard. The denominator varies far more: total rentable area of the building, total leasable area, occupied area only, or leasable area excluding anchor tenants in a retail centre.
Those choices produce different percentages, and the difference lands on every line below. Pull each tenant's stated share, recalculate it from the current rent roll, and compare. Where they disagree, the lease wins. Vacancy is the usual culprit: if a lease uses occupied area as the denominator, the share moves when a neighbour leaves, and a percentage sitting static in your system will be wrong.
Build the pool from the inclusion list, not from the expense accounts
Start from what the lease lets you recover and pull those costs in. Starting from the trial balance and removing what looks wrong is how excluded items survive to the statement.
Exclusions worth checking by name: leasing commissions, tenant inducements and fit-up costs, legal fees for negotiating leases or enforcing against another tenant, costs recovered from insurance or warranty, ground rent, financing costs, and repair of structural defects. Then look for anything you billed to a single tenant directly and left in the pool. That double-recovers.
Take the capital out, or amortize it the way the lease says
A capital expenditure is not an operating cost unless the lease makes it one. Many leases allow a defined slice: capital work required by a law that came into force after the lease date, or work undertaken to reduce operating costs, amortized over its useful life with an interest factor.
That clause has three moving parts and each is a place to go wrong. Amortize over the period the lease specifies, not the one your accountant would pick. Include the interest factor only where the lease grants it. Carry the schedule forward, because next year's statement picks up the same asset at the same rate.
Gross up only the costs that move with occupancy
A gross-up restates variable operating costs to what they would have been at a stated occupancy level, commonly 95 or 100 per cent. It stops a tenant in a full building from carrying a disproportionate share, and stops you absorbing the gap in a half-empty one.
The rule is narrow. Gross up costs that vary with occupancy and leave fixed costs alone. Cleaning, in-suite utilities and waste removal move with occupancy. Realty taxes, insurance, snow clearing, landscaping, elevator maintenance and security do not. Grossing up a fixed cost inflates the pool and is the easiest error here for a tenant to catch. If your lease contains no gross-up clause, you have no right to do it at all.
Apply caps and base year offsets in the order the lease sets
Read the cap clause literally. A cap can be annual or cumulative, and it can compound or not, and those give different ceilings by the fourth year of a term. A cumulative cap needs the prior years' figures, so last year's statement has to be in front of you before you can finish this one.
Where a lease uses a base year or an expense stop, confirm the base year amount you are subtracting was grossed up on the same basis as the current year. Comparing a grossed-up current year against a base year that was never grossed up understates the base and overbills the tenant every time.
Calculate the management fee last
The management or administration fee is a percentage, so it inherits every error above it. Finish the pool, then apply the fee to the base the lease defines. Some leases exclude realty taxes, insurance and utilities from that base. Some cap the fee outright. Applying the percentage to a grossed-up total where the lease sets it on actual costs is a routine finding in tenant audits.
Reconcile against what you billed, then deliver on time
Take the tenant's share of the finished pool, subtract the estimates you invoiced across the year, and the remainder is the shortfall or the credit. Invoiced, not collected: a tenant in arrears still gets credit for what was billed, and the arrears are a separate conversation.
Check your delivery deadline before you schedule the work. Many leases set an outside date for the statement, and some bar you from recovering a shortfall if you miss it. The same clause usually opens the tenant's audit window, and that window starts running on delivery.
Send the statement with the pool broken out by category, the proportionate share calculation with both numbers in the fraction shown, the gross-up and the occupancy figure you used, any amortization schedules, and the estimates billed. A statement carrying one total invites an audit. A statement that shows its work usually ends the question in an email.
The last check before it goes out
Run one test on the whole building. Add up every tenant's allocated share and compare the total to the recoverable pool. It should not exceed 100 per cent of what you are entitled to recover. If it does, you have a denominator problem, a vacancy that was never absorbed, or the same cost sitting in two categories. Find it now. That is a cheaper conversation than the one that starts when a tenant's auditor finds it.