Stress-Testing a Property Purchase in 2026: Why the Stressed Case Matters More Than the Base Case

The three shocks in a property stress test

Each shock targets a different way a comfortable deal becomes an uncomfortable one.

• —Interest rates +2%. Plintha's base modelling assumes 6.5% p.a. interest by default (overridable, and tagged [ASSUMED] in the report). The stress case adds two percentage points to whatever rate the model is using. On a large interest-only loan, the interest bill scales directly with the rate, so this shock lands on every dollar borrowed.
• —Extended vacancy. The base case carries a vacancy allowance of 3% of rent by default. The stress case asks a harder question: what does the position look like when the property sits untenanted for longer than the standard allowance assumes, while the loan, management, and maintenance costs keep running.
• —Interest-only expiry to principal-and-interest. An interest-only loan defers the principal; it does not remove it. When the IO period ends, repayments jump because the principal must now amortise over the remaining term. Plintha's default structure is an interest-only loan on a 30-year term, so the expiry cliff is modelled rather than ignored.

Why the base case flatters almost every deal

A base case is a set of assumptions that mirror conditions at the moment of purchase. Plintha's defaults — 80% LVR, interest-only, property management at 8% of rent, maintenance at 0.7% of the price per year — are deliberately visible and overridable, and every figure in the report carries provenance: computed, [ESTIMATE], or [ASSUMED]. But even scrupulously honest assumptions describe the present. A property is held for years, and over years the rate environment, the tenancy, and the loan structure will all move.

The base case tests whether a buyer can afford to buy. The stressed case tests whether an owner can afford to hold. Deals rarely fail on settlement day; they fail in the gap between the good day the numbers were run on and the bad year that eventually arrives.

The 2026–27 Budget raised the price of failing

Since the 12 May 2026 Budget, an established property purchased after that date has its rental losses quarantined: they carry forward against future rental profits or the eventual capital gain, and cannot be deducted against salary. In a stressed year, that changes the arithmetic materially. A shortfall that would once have been softened by a deduction against other income is now met from household cash in full, with the tax relief deferred to some later year.

New builds purchased or contracted from 12 May 2026 keep the ability to deduct rental losses against other income, and properties owned or contracted before that date are grandfathered under the old rules. This is why Plintha classifies every property as grandfathered, new build, or established post-budget before modelling tax — the class determines not just the tax outcome, but how painful a failed stress test is in cash terms.

What a pass or fail should change about the decision

A failed stress test is information, not a verdict on the suburb or the buyer. It says the deal works only while conditions stay benign. The general responses are structural: a lower LVR (more equity shrinks the interest bill, and Plintha's model only adds LMI above 80%), principal-and-interest from day one so there is no expiry cliff, a larger cash buffer, or a different property at a different price point.

A pass means the deal survives its bad year on paper — which is worth exactly as much as the inputs behind it. This is why Plintha's reports tag every figure with its provenance, and why the stress test runs on every analysis rather than as an optional extra. The free tier includes one full analysis a month, with no card required, so the stressed case can be examined before any money moves.

Common questions