📖 Commercial lease glossary
Pro Rata Share (Tenant's Proportionate Share)
Pro rata share is the percentage of a building's shared costs that a single tenant pays, calculated as the tenant's leased rentable square footage divided by the total rentable area the lease defines, expressed as a percentage. A tenant leasing 6,000 rentable square feet in a 30,000-square-foot building has a 20% pro rata share and owes 20% of whatever expense pool the lease passes through — CAM, property taxes, insurance, or a blended operating-expense bucket. Latin for "in proportion," it is the single number behind nearly every additional-rent invoice in a multi-tenant property, and the lease's definition of the denominator decides more than most tenants ever check.
How pro rata share is calculated
The formula has three parts: the numerator (the square footage of the tenant's premises), the denominator (the total area the lease designates for allocation, sometimes called the "Defined Area"), and the expense pool the share is applied to. Pro rata share = (premises RSF ÷ Defined Area RSF) × 100. The tenant's dollar obligation is then that percentage multiplied by the pool for the period: (premises ÷ denominator) × eligible expenses.
Worked example: a tenant leases 6,000 rentable square feet in a 30,000-square-foot building, so its pro rata share is 20%. The landlord's eligible operating-expense pool for the year totals $320,000, making the tenant's share $64,000 — typically billed monthly as an estimate and trued up at year-end through the reconciliation statement.
Some leases state the share as a hard-coded percentage ("Tenant's Share: 20.00%") rather than as a formula, which makes it easy to verify but also easy for a stale figure to survive a re-measurement. Others define it only fractionally and let it recompute as the building's occupancy changes. Which version the lease uses is itself a negotiated term.
The denominator is the negotiation
The same tenant square footage produces different bills depending on what the lease puts in the denominator. The two standard measures are Gross Leasable Area (GLA) — every leasable foot in the building, occupied or vacant — and Gross Leasable Occupied Area (GLOA), which counts only occupied space. A GLA denominator gives the tenant a smaller, stable share; a GLOA denominator raises the sitting tenants' percentage every time a neighbor moves out, concentrating the vacancy's cost on the tenants who stayed. A lease that pins the denominator to the building's full rentable area is the tenant-favorable position, and it is the single most valuable sentence in the allocation clause.
Occupancy-based denominators usually come with stipulations to stop abuse: "not less than 95% of GLA," or the same floor used in the gross-up clause. Watch for leases that use different denominators for different pools — office-space square footage for CAM but site square footage for taxes and insurance in multi-building properties — and for re-measurement rights letting the landlord recalculate shares after a renovation trims or adds common area.
Expansion and contraction also move the number. Leases that add space by amendment should restate the share expressly; where they don't, the abstract must record the recomputed percentage against the new premises footage, because invoices generated from the original figure silently underbill or overbill from that point forward.
What pro rata share applies to — and what it doesn't
Pro rata share governs allocation of shared costs: common area maintenance, property taxes, property insurance, shared utilities, and management overhead where the lease passes them through. In a triple-net structure the same percentage is applied to three separately audited pools; in a modified-gross structure it applies to the excess over a base year; in a full-service gross lease the landlord absorbs the pools and the share appears only if the lease converts to a different structure.
It does not apply to charges that are personal to the tenant. Base rent is a fixed obligation, not a share of anything. Percentage rent keys off the tenant's own sales against a breakpoint. Submetered utilities, dedicated phone or internet service, and damage repairs charge the tenant directly. A property manager who applies a 20% share to something that should be billed 100% to the tenant — or bills a shared cost directly — is the most common source of lease-audit findings.
The boundary matters at abstracting time because recovery systems in Yardi or MRI configure the share once and bill it forever: the numerator, the denominator definition, and which pools use that share each need to be captured as separate data points, with the lease language behind them, so a later re-measurement or expansion update is traceable.
Negotiating and verifying the number
Tenants should ask four questions before signing: What exactly is in the denominator (GLA, GLOA, or a stated figure)? Is there a floor so vacancy can't inflate my share? Can the landlord re-measure and recompute unilaterally? And are the same inputs used across every pool, or does each article allocate differently?
Auditors verify a billed share the same way in reverse: recompute premises ÷ denominator from the lease's own definitions, compare against the percentage on the statement, and test whether the denominator shrank between years. A share that climbs with no amendment behind it — from 20% to 25% because four suites went dark — is the finding that usually repays several years of over-allocated expense.
Frequently asked questions
Is pro rata share always based on square footage?
Almost always, but not necessarily. The lease defines the numerator and denominator, and office leases typically use rentable square feet while industrial and retail leases may use a stated percentage, unit count, or frontage-based share. Whatever the lease names as the basis is what governs — a tenant billed on a percentage that no measurement in the document supports has a reconciliation issue.
What is the difference between pro rata share and gross-up?
Pro rata share divides the expense pool among tenants; a gross-up clause first scales the variable portion of the pool up to a stipulated occupancy level before that division happens. Gross-up changes the size of the pie being shared; the pro rata denominator changes whose slice is bigger. Both turn on the same vacancy economics, which is why leases that stipulate a minimum occupancy for allocation use one or the other, never both simultaneously for the same costs.
Can a landlord change my pro rata share mid-term?
Only as the lease allows. A fixed stated percentage stays put unless the parties amend it or the lease grants an express re-measurement right. A formula-defined share moves automatically when the premises or the Defined Area changes — expansion, contraction, or a reconfiguration of common area. Tenants who want stability negotiate a stated figure or a denominator floor; landlords who want precision reserve the right to recalculate.
Why does my pro rata share keep going up even though the building costs are flat?
Because the denominator, not the pool, is usually the moving part. If the lease allocates on occupied area and neighbors vacate, the same dollars get divided among fewer feet and every remaining tenant's percentage rises. That is why the denominator definition is the first thing a lease audit checks when additional rent climbs without any change in the expense statement's line items.
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