A multifamily building can be 95% physically occupied yet collect only 83.25% of its market rent potential, as the hypothetical example below shows. An economic occupancy calculation measures that rent performance: divide rental income collected or recognized by potential rent for the same period, then multiply by 100. The income basis and denominator determine what the percentage tells you.

Physical vs economic occupancy: units and dollars

Physical occupancy measures occupied apartments as a share of the units counted. For a snapshot, divide occupied units by total units. For a monthly average, occupied unit-days divided by total unit-days accounts for move-ins and move-outs; a month-end snapshot can miss those changes.

Economic occupancy measures rent performance. It gives different weight to apartments with different rents and captures reductions that an occupied-unit count cannot show. An occupied apartment can have a below-market lease, a free-rent incentive or an unpaid balance.

For multifamily investment analysis, label the property scope, period, income basis and denominator beside the percentage. Keep residential rent separate from parking, laundry and other income when measuring residential rent performance.

Choose market rent or scheduled lease rent

Two denominators answer different questions:

• Market rent potential is what all apartments would generate at supported market rents for the period. The difference between market rent and existing lease rent on occupied units is commonly called loss to lease. Above-market leases can produce a gain instead.
• In-place rent potential combines existing lease rents before concessions and collection losses with an explicitly assigned rent for vacant units. Using market rent for vacant units keeps them in the denominator while reflecting occupied units’ lease terms.

Market rent potential helps identify the difference between current leases and market pricing. A higher market-rent estimate can lower economic occupancy without changing collections. In-place rent potential focuses on performance against existing leases and the stated vacant-unit assumption.

Dividing collections only by occupied tenants’ scheduled charges produces a collection measure that excludes vacant-unit potential. It cannot describe the whole building’s rent performance.

Gross potential rent reconciliation: a 95% occupied building

Assume a hypothetical 20-unit property for July 2026, measured as of July 31. Nineteen apartments are occupied throughout the month; one is vacant throughout. Every apartment has a supported market rent of $2,000, while each occupied apartment’s lease specifies $1,900 before concessions.

This calculation uses July residential rent collected by July 31. Assume no receipts for earlier or later months, security deposits, ancillary income, non-revenue units or midmonth lease changes. July concessions total $1,000. Of the remaining charges, $1,200 is still outstanding and considered collectible, while a separate $600 has been deemed uncollectible and written off.

The $1,000 concession is an agreed rent reduction. Delinquency is rent still owed; bad debt identifies an amount treated as uncollectible. Here, the two unpaid categories contain different dollars.

Using the same property and period produces three results:

• Physical occupancy: 19 ÷ 20 × 100 = 95%.
• Economic occupancy against market rent: $33,300 ÷ $40,000 × 100 = 83.25%.
• Economic occupancy against in-place rent potential: $33,300 ÷ $38,100 × 100 ≈ 87.40%.

The last denominator contains $36,100 of occupied lease rent plus $2,000 for the vacant apartment. Loss to lease has already been removed from that starting point.

Only $2,000 of the $6,700 gap against market potential comes from an empty apartment. Filling that unit cannot, by itself, eliminate the concessions, collection shortfall or difference between lease and market rents. Those distinctions matter when evaluating rental income and operating economics.

Agency underwriting uses its own conventions

The example is a management diagnostic. Agency underwriting follows specified conventions and additional adjustments.

In the guide edition effective June 2, 2026, Fannie Mae’s conventional-loan income table, pages 119–120, starts with occupied units’ actual rents plus vacant units’ market rents, annualized. It separately deducts physical vacancy, concessions and bad debt.

Freddie Mac’s June 2022 appraisal guidance likewise emphasizes actual lease terms for an as-is valuation. It explains that potential income already based on the current rent roll does not need another loss-to-lease deduction. The management calculation above does not replace either agency’s underwriting requirements.

Why the rent roll and trailing operating statement disagree

A rent roll describes leases and unit status as of a date. A trailing twelve-month operating statement, or T12, records activity over a year. Multiplying the July 31 rent roll by twelve will not reproduce income from August 2025 through July 2026 if rents, occupancy or incentives changed during that period.

Accounting timing adds another difference. Collections exclude unpaid rent, while accrual income can include earned rent that remains collectible but unpaid. Concessions may also be spread across a lease instead of appearing entirely in the month the tenant receives free rent. For example, AvalonBay’s 2025 Form 10-K, filed February 27, 2026, describes spreading concessions evenly over lease terms.

Freddie Mac’s conventional underwriting checklist dated December 16, 2025 calls for a certified rent roll, historical financial statements including a T12, and a certified aged-receivables report when applicable. A rent roll alone cannot establish collections.

To reconcile the records, trace each month’s charges, concessions, receipts, write-offs and remaining receivables before aggregating the year. Identify receipts for earlier months and prepaid future rent separately. For a period-matched collection metric, allocate receipts to the rent period; retain a separate reconciliation to cash received during the month.

Avoid counting the same income loss twice

Follow each deduction from its starting balance:

• Vacancy: If the starting figure contains only occupied lease charges, vacant rent is already absent. Add vacant-unit potential before making a separate vacancy deduction.
• Loss to lease: Deduct it from an all-market-rent starting point. Do not deduct it again from a figure already using occupied units’ actual lease rents.
• Concessions: Check whether the rent roll shows face rent or rent already reduced by incentives. Subtract an incentive only once.
• Unpaid rent: Actual collections already exclude unpaid dollars. Do not subtract bad debt again from collected rent, or treat the same balance as both delinquency and bad debt.

In the example, the $600 write-off explains part of the reconciliation from charges to cash; it does not reduce the $33,300 cash total again. If the $1,200 outstanding balance is later written off, changing its classification creates no additional cash shortfall.

For property operations, keep each balance traceable by tenant and charge month. Before using the reconciliation in financing, confirm the income basis with the property accountant and the required denominator and underwriting adjustments with the lender.