Worked example: occupancy falls on a stabilized property

When occupancy falls, collected rent drops by the full rent of each vacated unit while only a small share of operating cost goes away, so NOI declines by more than rent does as a share of revenue. The hypothetical deal below produces three different answers from one operating model: whether NOI still covers debt service, whether it clears an assumed coverage covenant, and how much cash remains after debt service. The gaps between those three breakpoints are where a property can keep paying its lender and still fail a test.

Why lost rent outruns saved expenses on an apartment property

Occupancy reaches cash flow through the expense structure. A vacated apartment stops paying rent, but the costs of owning the building carry on. Debt service and real estate taxes keep running when rental income falls, and insurance and maintenance costs generally do too. Common-area costs and utilities may not decline either.

For this exercise, NOI is total property revenue less direct property operating expenses, with property taxes inside the expense line. Debt service and other financing costs sit below NOI. Definitions of NOI differ on the word taxes: one industry glossary describes NOI as income after operating expenses but before taxes and financing expenses. A stress model therefore needs a written definition, because moving property taxes across the NOI line changes the coverage ratio without changing a dollar of cash.

The useful unit is contribution per occupied unit: the rent a unit pays minus the expenses that actually move when that unit is occupied. Contribution from all occupied units first absorbs the costs that never move. Only the remainder reaches debt service.

Fixed obligations also raise the cost of vacancy on the debt side. Debt service and property taxes keep running when income drops, so a tenant default or delayed lease-up has a larger effect on a levered property than the lost rent alone suggests.

Underwriting stress tests formalize this as a breakeven analysis on NOI. In addition to the usual debt service coverage ratio and loan-to-value criteria, a stress test may find the point where NOI breaks even by raising operating expenses or lowering rents. Occupancy is the same test applied to the revenue line.

“Expenses associated with our investment in these communities, such as debt service, real estate taxes, insurance and maintenance costs, are generally not reduced when circumstances cause a reduction in rental income from the community.”

Worked example: occupancy falls from 95 percent to 80 percent on 100 apartments

The hypothetical property has 100 apartments, each renting for $2,000 per month. Both cases use the same property, the same loan and the same twelve-month period. Annual debt service is $1,000,000 and covers every debt payment requiring current payment. No financing fees are added in either case, no new equity enters, and capital expenditures and leasing costs are excluded, so the residual below is cash after debt service before those uses. Every occupied apartment pays in full, so physical occupancy and rent-paying occupancy are the same.

Annual rent per apartment is $2,000 multiplied by 12, or $24,000, and full occupancy would collect 100 multiplied by $24,000, or $2,400,000. Operating costs split into two pools. Fixed operating expenses, including property taxes and insurance, are $500,000 and do not move with occupancy. A variable pool is $400,000 at full occupancy, which is $4,000 per apartment ($400,000 divided by 100). That proportional response is an assumption about this pool only.

Contribution per occupied apartment is $24,000 minus $4,000, or $20,000. Every apartment that leaves removes $20,000 of NOI, because its rent disappears and only $4,000 of cost goes with it.

Base case, 95 apartments occupied. Collected rent is 95 multiplied by $24,000, or $2,280,000. Variable expenses are 95 multiplied by $4,000, or $380,000. Total operating expenses are $500,000 plus $380,000, or $880,000. NOI is $2,280,000 minus $880,000, or $1,400,000. Debt service coverage is $1,400,000 divided by $1,000,000, or 1.40x, and cash after debt service is $1,400,000 minus $1,000,000, or $400,000.

Stressed case, 80 apartments occupied. Collected rent is 80 multiplied by $24,000, or $1,920,000. Variable expenses are 80 multiplied by $4,000, or $320,000. Total operating expenses are $500,000 plus $320,000, or $820,000. NOI is $1,920,000 minus $820,000, or $1,100,000. Coverage is $1,100,000 divided by $1,000,000, or 1.10x, and cash after debt service is $1,100,000 minus $1,000,000, or $100,000.

The bridge between the cases runs through 15 vacated apartments (95 minus 80). Rent falls by 15 multiplied by $24,000, or $360,000. Variable expenses fall by 15 multiplied by $4,000, or $60,000. NOI therefore falls by $360,000 minus $60,000, or $300,000, which equals 15 multiplied by $20,000.

Debt-payment breakpoint. NOI must reach $1,000,000 to cover debt service. Fixed expenses plus debt service total $500,000 plus $1,000,000, or $1,500,000, and dividing by $20,000 per apartment gives 75 apartments, or 75 percent occupancy. The check: rent is 75 multiplied by $24,000, or $1,800,000, variable expenses are 75 multiplied by $4,000, or $300,000, and NOI is $1,800,000 minus $500,000 minus $300,000, or $1,000,000, leaving $0 after debt service.

Covenant breakpoint. The covenant case assumes a separate loan covenant of 1.25x coverage on the same NOI definition and the same debt service. Required NOI is 1.25 multiplied by $1,000,000, or $1,250,000. Contribution needed is $500,000 plus $1,250,000, or $1,750,000, and dividing by $20,000 gives 87.5 apartments, or 87.50 percent occupancy.

Taken together, the base case clears the assumed covenant by $150,000 of NOI ($1,400,000 minus $1,250,000), which is 7.5 apartments of cushion ($150,000 divided by $20,000). The stressed case misses the covenant by $150,000 ($1,250,000 minus $1,100,000) while sitting 5 apartments above the debt-payment breakpoint (80 minus 75), worth $100,000 of NOI. Occupancy has to fall 20 points from the base case (95 minus 75) before debt service goes unpaid from operations, but only 7.5 points (95 minus 87.5) before the assumed covenant trips. The 12.5 point gap between them (87.5 minus 75) is where a property pays its lender in full and still fails the test. What follows a covenant miss depends on loan terms the model does not assume.

How net leases and reimbursements change the vacancy bridge

The apartment example puts every operating cost on the owner during occupancy, which is why a vacated unit removes rent and almost no expense. Commercial leases allocate costs differently, and the allocation controls the vacancy bridge.

Under a long-term net lease the tenant pays property operating expenses, including real estate taxes and insurance along with maintenance, either directly or by reimbursement. While the space is occupied, the owner’s NOI looks insulated from those costs. When the space goes vacant, no tenant remains to pay them, so the vacancy case must assign those costs to the owner for the empty space.

Two reporting arrangements need different bridges even when their occupied economics look alike. If the tenant pays a bill directly, that payment may never appear in the owner’s receipts, and vacancy adds an owner expense that was previously off the statement. If the owner pays the bill and collects a reimbursement, vacancy removes a revenue line while the bill continues. Both arrangements end in the same vacant-state cost, but the model reaches it through opposite line items.

A label such as net lease does not supply the number. The amount of lost reimbursement and the owner’s remaining obligations follow the specific lease terms, tenant by tenant.

Apartment properties add a different timing question. They require active management, frequent renovation and maintenance, and the timing of that work is not set by occupancy. The worked example isolates the occupancy effect by excluding capital items, and a fuller cash schedule shows them as separate uses.

Annual coverage, rent-paying occupancy and the monthly gap

An annual coverage ratio says whether a full year of NOI covers a full year of debt service. It does not say whether cash arrives before the payments fall due.

One regulatory definition ties the concept to cash. Sustaining occupancy is rent-paying tenant occupancy under signed leases sufficient to cover monthly operating expenses and debt service, including any subordinate debt requiring current payment. The definition has three working parts: the tenants must be paying, the test is monthly, and every currently payable debt counts.

A signed lease without current rent payments is not a current receipt, and a physical occupancy count says nothing about collections. Two properties at the same physical occupancy can produce different cash if collection assumptions differ.

A monthly reconciliation starts with opening cash, adds collected rent, subtracts operating and debt payments, and carries the closing balance forward. If receipts arrive after obligations fall due, the sequence can go negative in a month even when the year ends with cash after debt service.

The denominator also matters. A test that includes subordinate debt requiring current payment divides by a larger number than one limited to the senior payment, and the same NOI produces a lower ratio. The worked example assumes its stated annual debt service holds every payment being tested.

Pitfalls in occupancy stress models

Scaling the entire expense budget with occupancy overstates savings. Applying the occupancy factor to property taxes, insurance or other continuing costs assigns a reduction that does not occur. Separating the fixed pool from the variable pool, as the example does, shows that the lost contribution per unit is rent minus only the costs that move.

Placing debt service inside NOI counts the financing cost twice once coverage is calculated. NOI stops before financing, and coverage divides NOI by the debt payment. With debt service already deducted, the ratio understates the property and the two statements no longer reconcile.

Using one occupancy figure for both vacant space and unpaid rent hides the revenue mechanism. The same physical occupancy can produce different receipts when payment behavior differs. Holding occupancy and collections as separate inputs shows whether the modeled loss comes from empty units or from nonpayment.

A single break-even label confuses operating solvency with debt capacity. Revenue that covers operating expenses leaves the debt payment unresolved, and revenue that covers both still leaves excluded capital spending unresolved. In the example, break-even at the debt payment and the covenant threshold sit 12.5 points of occupancy apart.

Reading positive cash after debt service as a passed covenant answers the wrong arithmetic question. A coverage covenant compares a defined income measure with a defined debt obligation at a stated multiple. The stressed case shows $100,000 of residual cash alongside a 1.10x ratio that sits below an assumed 1.25x threshold.

Questions a reviewer asks of an occupancy stress

Does occupancy mean physical use or tenants currently paying rent? A signed lease and an occupied unit each need a payment assumption before either becomes collected revenue.

Which property expenses continue when rental receipts fall? A schedule of continuing costs shows what absorbs the remaining revenue first.

Which expenses change with occupancy, and by what arithmetic? A stated cost relationship makes the assumed savings reproducible.

Where do property taxes and financing costs sit relative to NOI? Consistent classification keeps property NOI separate from cash after debt service.

How do reimbursements and direct tenant payments enter the vacancy case? The lease allocation decides which receipts disappear and which obligations land on the owner.

Does the modeled debt service include subordinate obligations requiring current payment? The denominator has to match the scope of the coverage question being asked.

Which income definition and measurement period govern the assumed coverage test? A ratio computed on a different basis cannot show how that test comes out.

At what occupancy does NOI reach each breakpoint, the debt payment and the covenant? Expressing both in units shows how many vacancies separate a passing test from a failed one.

What cash uses sit outside the residual? Excluded capital spending and leasing costs mean cash after debt service is not fully available for distribution.