Tenant default is when a tenant fails to meet lease obligations in a way that triggers contractual remedies after notice and cure, not merely when a check arrives late. Vacancy is any space that stops producing contractual rent, including economic vacancy from abatements, rent holidays, and rent billed but not collected. In downside models, these two turn valuation into liquidity, and lenders lend against liquidity.
Tenant default and vacancy are the two fastest ways a real estate downside case becomes unfinanceable. They force you to ask a simple question: “When does cash fall short, and who controls the checkbook at that moment?” A credible stress test does not start with a cap rate. It starts with lease contracts, tenant balance sheets, property-level cash controls, and the precise month debt service or covenants fail.
The goal is not to “be conservative.” The goal is to avoid false precision and identify which assumptions actually drive leverage sizing, reserves, pricing, and governance. If you can’t point to the document that supports the input, you’re guessing. And guessing looks fine right up until it doesn’t.
Definitions that keep your underwriting honest
Clear boundary conditions prevent a model from drifting into vibes. Default must map to a contract state you can audit: delinquency, event of default, termination, or rejection in bankruptcy. Models often use “default” as a mood, but the lease uses it as a trigger.
Accurate vacancy assumptions also require clean categories. Vacancy must be split into physical vacancy and economic vacancy. Physical vacancy is empty space, while economic vacancy includes abatements, free rent, and rent that is owed but not collected.
Credit loss from tenancy has three components, and they should not be blended into one “vacancy factor.”
- Non-payment risk: Probability and timing of non-payment on occupied space.
- Conversion to vacancy: Probability and timing of termination or bankruptcy rejection that converts occupied space into vacant space.
- Re-leasing severity: Loss severity on re-leasing, including downtime, tenant improvements (TIs), leasing commissions (LCs), and rent reset versus in-place rent.
Bad debt is a reporting line that often hides more than it reveals. “Bad debt” in operating statements is often incomparable across owners because write-off policies differ. One owner writes off at 60 days; another carries receivables for 180 and later recovers some. Separate the lines: billed rent, collected cash, contractual abatements, and write-offs. If the sponsor can’t reconcile those to the lease schedule and bank statements, the stress test is floating.
Why default and vacancy shocks break downside models
Most base cases assume continuity, which is exactly what default disrupts. Rent steps happen, expenses rise, vacancy mean-reverts, and then one tenant stops paying and the timeline matters. Default and vacancy introduce path dependency, meaning the sequence of events drives outcomes, not just the average.
Timing creates the real damage because costs arrive before stabilization does. A tenant that stops paying in month three creates costs immediately and pushes leasing into whatever season you land in. That timing then compounds into covenant pressure, deferred maintenance, and slower leasing velocity. You do not get to average your way out of a cash trough.
Cash is the enforcement layer, so mis-timing cash breaks the model. Many models fail because they mis-time cash. Accrual rent is not cash rent. Loan documents and reserve mechanics are cash-driven. The critical question is when cash NOI falls below debt service, required reserve funding, lender cash sweep triggers, DSCR tests, and any springing LTV covenants.
Market context should change your default posture without replacing asset-level work. As a market check, CMBS office delinquency reached 9.98% as of Dec-2023 (Trepp). That number does not tell you what your building will do. It does tell you to treat tenant and leasing shocks as first-order underwriting risks when rollover is heavy and tenant quality is thin. If you are underwriting a leveraged deal, link this section back to your debt sizing and coverage ratios assumptions rather than treating delinquency as a headline statistic.
A committee-auditable stress-testing architecture
A stress test should be modular so every assumption has a home and a document hook. Build the framework as linked modules with clear inputs, contract hooks, and failure modes. If you can’t produce the schedules cleanly, the downside is probably being smoothed.
Lease-level cash schedule (tenant-by-tenant)
The lease is a cash instrument, so start there. For each tenant, input base rent steps and payment cadence, recovery structure (gross, base year, NNN), free rent and abatements, renewal options and notice windows, security deposit or letter of credit (LOC), guarantees and scope, and termination rights and notice/cure periods.
The output should be a monthly cash view that a lender could follow. Output billed rent, contractual abatements, assumed non-payment, assumed recoveries (deposit/LOC draws), and net cash collected. Treat each tenant as a credit exposure with a maturity schedule. The loan sits senior to equity, but the tenant’s payment sits upstream of both. No rent, no deal. If you need a cleaner build process, align the schedule to a lease-driven structure like this guide on modeling rent rolls and leases.
Default timing module (when does non-payment occur)
A timing module forces explicit assumptions about onset and cure. Two workable approaches are deterministic stress (pick named tenants or cohorts and impose non-payment starting in a defined month) and stochastic overlay (hazard rates by tenant tier with scenario-based draws).
Deterministic stress is usually more decision-useful in an investment committee. In committees, you can run kill tests tied to the top five tenants, near-term rollover, or the one tenant whose loss would trip the lockbox. Default onset should resemble real behavior because partial payments, delayed CAM true-ups, and disputes often show up before a clean stop. A model that assumes “paying until expiry, then gone” misses the cash trough that drives covenant trips.
Space disposition module (what happens after non-payment)
Non-payment does not automatically create vacancy, so you must model the fork in the road. The landlord might negotiate a workout, accept a surrender, terminate and re-let, litigate, or deal with bankruptcy. Each path changes cash timing and costs.
A workout must be modeled as a new contract with new economics. If management says “workout” but keeps rent flat and adds concessions for free, the model is not describing a workout. It is describing hope.
Re-leasing module (downtime, economics, and capex)
Re-leasing assumptions are where many downside cases quietly hide. A credible module requires downtime assumptions grounded in asset type and market, market rent reset versus in-place rent, TI and LC tied to lease term and tenant type, costs for second-generation space, and timing of TI spend versus rent commencement.
Asset type changes how the stress shows up, so avoid copy-paste inputs. Office and retail are especially sensitive to TI and downtime. Industrial usually carries lower TI, but rent reset risk still bites if in-place rents are above market. Multifamily stress often shows up as concessions rather than long vacancy; the cash effect can be similar. If you want a practical reference point for concessions and vacancy mechanics, see Breaking Into Wall Street: Real Estate Concessions, Vacancies, and Reimbursements.
Lender control module (who controls cash and when)
A lender control module turns property stress into sponsor liquidity stress. Capture lockbox and cash management terms, springing sweeps based on DSCR or debt yield, replacement reserve requirements, TI/LC reserve funding formulas, conditions to release reserves, and default interest and fees after an event of default.
Skipping cash control mechanics is a common way equity models overstate flexibility. If the model skips lockbox mechanics, it overstates equity control in the month you need control most. Leasing and capex require cash at the same time a lender may restrict distributions and sweep cash.
Tenant credit assessment that actually feeds the model
Tenant credit work should change hazard rates and loss severity, not live in a memo appendix. Default risk is not “rated or unrated.” Many tenants are private, thinly capitalized, or structured to keep assets away from the lease. You can still tier risk with observable indicators.
- Rent-to-sales: Use it where sales exist to spot tenants that cannot carry occupancy costs through a downturn.
- Industry margin proxy: Apply industry-level operating margin expectations to sanity-check coverage and dispute risk.
- Store-level performance: For retail, focus on unit economics and co-tenancy exposure, not just corporate logos.
- Footprint trends: For office, track headcount and space strategy to avoid underwriting a shrinking user as stable.
- Guarantee strength: Underwrite parent guarantee scope, caps, burn-offs, and enforceability as a real recovery source.
- Cross-default hooks: Note provisions across locations that can accelerate negotiations or accelerate failure.
Transparency is itself a credit input because missing financials increase tail risk. For public tenants, market prices often tell you whether stress is rising. For private tenants, ask whether the tenant can be underwritten like a small corporate borrower. If basic financials are unavailable, raise hazard rates and loss severity. Lack of transparency is a risk factor, not a rounding error.
Legal mechanics that drive recoveries and timing
Legal friction determines whether recoveries are collectible and when cash arrives. Stress tests often ignore legal friction, but legal friction decides whether a modeled recovery is collectible and when you can collect it.
Security deposits vs. letters of credit
Deposits and LOCs behave differently under stress, so you should not treat them as interchangeable. Deposits may be commingled unless the lease requires segregation. An LOC is a bank obligation if drafted and drawn correctly.
LOCs are often easier to monetize in stress, but only if the beneficiary matches the landlord entity, draw conditions are workable, expirations are monitored and extended, the issuing bank is sound, and the lease permits draws for non-payment and other defaults. Don’t treat deposits and LOCs as interchangeable. Time the draw and include administrative lag and counsel time, because that lag can be the difference between staying current and tripping a sweep.
Guarantees and their limits
Guarantees only work to the extent they are designed to pay. Guarantees have caps, burn-offs, and carve-outs. A “good guy” guarantee may support surrender, not full rent recovery. Model the guarantee as a defined recovery with a defined timing, not as a blanket backstop.
Bankruptcy and lease rejection
Bankruptcy changes remedies and timing, so the modeling point is the cash trough. Bankruptcy can turn a collectability issue into a vacancy issue. The U.S. Bankruptcy Code governs treatment of unexpired leases, and the modeling point is timing. Even if you regain the space, the cash trough and legal expense arrive first. For cross-border portfolios, enforcement and insolvency timelines vary by country, so apply country-specific timing and recovery assumptions rather than one global vacancy shock.
Documentation that makes a downside case defensible
A lender-quality downside case traces every major input to an executed document. The list is smaller than most data rooms suggest, which makes it easier to run diligence with a checklist mindset.
- Lease documents: Lease agreements and amendments that control rent, options, deposits, and remedies.
- Tenant confirmations: Estoppels and waivers where available to confirm economics and reduce disputes.
- Collections proof: Rent roll and aged receivables to anchor billed versus collected.
- Recoveries history: CAM and tax reconciliation history to show recovery realization and dispute risk.
- Future cash claims: TI/LC history and open commitments that create forward funding needs.
Cash controls should be documented with the same discipline. Loan agreement, cash management agreement, lockbox instructions, reserve agreements and disbursement conditions, and intercreditor agreements (if mezzanine or preferred equity exists) determine who can act in a downturn. If modeled economics aren’t supported by executed amendments, the stress test is ungrounded.
Modeling mechanics that reduce false precision
Small modeling choices often decide whether a downside case is real or decorative. Modeling mechanics matter because they determine whether you capture the trough that triggers lender action.
Model rent in cash, not accrual
Cash modeling prevents you from confusing occupancy with collections. Run two lines per tenant: contract rent per the lease schedule and a collection rate that converts contract rent into cash under stress. Collection is not occupancy. A tenant can occupy and not pay, and a tenant can vacate and still pay during a negotiated wind-down. Your model should allow both, or it will miss the period that matters.
Treat downtime as a distribution, not a point
Downtime is uncertain, so a single input invites overconfidence. Model at least three states: fast lease-up, base lease-up, and slow lease-up. Pair each with TI/LC and rent reset assumptions. Downtime and rent are linked. Higher rent assumptions usually require more time and more concessions. If you assume higher rent with shorter downtime, you are paying yourself twice. This logic should sit inside your broader downside and stress testing framework.
Expenses do not scale neatly with occupancy
Expense behavior is a frequent source of understated cash burn. Vacancy reduces some variable costs, but it also increases leasing, turnover, and sometimes security and utilities. Property taxes rarely fall quickly, and insurance can rise after claims or repricing. If you scale expenses linearly with occupancy, you understate the trough.
TI and LC timing can trigger liquidity failure
Front-loaded leasing costs are often the real breaking point. Landlords can survive lower rent with liquidity. They often fail on a big TI draw paired with free rent. Time TI spend during build-out, time LC at execution, and start rent after delivery. Don’t amortize TI/LC and call it a day. Valuation may spread it; cash management cannot. For a deeper build, align with best practices on modeling capex and tenant improvements.
A fresh angle: the “cash-control gap” test
The highest-value stress tests don’t just predict losses; they expose operational dead zones. A useful non-boilerplate check is to measure the cash-control gap: the number of days between when a leasing decision must be made (signing a new lease or funding TI) and when you can reliably access cash to execute it (reserve release, lender consent, or capital call funding).
This gap is easy to miss because underwriting often assumes cash is available if the IRR is high enough. In reality, a lockbox sweep, a reserve trap, or slow investor funding can turn a solvable leasing problem into a technical default. As a rule of thumb, if your modeled minimum cash balance occurs within the same quarter as a major TI package, you should assume lender involvement and build a consent timeline into the schedule.
Decision-useful outputs for investment committees
A tenant default and vacancy stress test should produce three clean outputs that are easy to debate. When those outputs are clear, committee discussion shifts from “what cap rate” to “what breaks first, when does it break, and how do we finance through it.” That is where sound underwriting lives.
- Tenant exposure table: Top tenants, expiry, annual rent, deposit/LOC, guarantee status, and credit tier.
- Monthly cash and covenant schedule: Cash collections, operating costs, reserves, debt service, DSCR, sweep status, and ending cash.
- Re-leasing sensitivity grid: Downtime and rent reset combinations tied to TI/LC packages, with impact on minimum cash and loan compliance.
Archiving should be treated as part of risk management, not admin. Archive the model package and inputs (index, versions, Q&A, users, full audit logs) and hash the final set. Set retention periods that match policy and loan requirements. Require vendor deletion with a destruction certificate when retention ends. Legal holds override deletion.
Closing Thoughts
Tenant default and vacancy underwriting is ultimately about cash timing and control, not just valuation. If you define default and vacancy precisely, model cash at the lease level, and connect shocks to lender triggers and reserve mechanics, you get a downside case that can actually be financed and managed.
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