Most calculators run one check. Lenders run all three — and reject you if you fail any of them. The afford floor checker does the same thing, upfront.
The tool has two modes. Forward mode: given your savings and income, what is the highest price you can reach? Backward mode: given a target price, is it achievable? If not, what is your actual maximum and what would need to change?
Finding the maximum purchase price is circular. Stamp duty depends on the price, and LMI depends on how much deposit is left after stamp duty — which depends on the price. There is no algebraic shortcut.
The tool solves this with a binary search: it tests candidate prices between $0 and $5M, converging on the highest price where your savings cover all upfront costs and the resulting loan stays within the relevant ceiling. Each iteration halves the search range; after 60 iterations the answer is accurate to the nearest dollar.
This same approach is used for all three ceilings. The stamp duty and LMI calculations run at every candidate price — which is why bracket data is read live from Supabase rather than hardcoded.
The deposit floor answers: what is the highest purchase price your savings can reach, after all upfront costs are paid? This is often the most surprising ceiling — stamp duty and LMI can consume $30,000–$80,000 before a dollar goes toward deposit.
Upfront costs
For each candidate price, the tool deducts three upfront costs from your savings before calculating available deposit:
The LMI circularity
LMI creates a second circular dependency inside the first: LMI stamp duty reduces available deposit → changes loan size → changes LMI premium → changes LMI stamp duty. The tool resolves this with an inner loop of 6 iterations starting from LMI stamp duty = 0. It converges within 3 iterations in practice; 6 is conservative. States with no LMI stamp duty (NSW, ACT) exit in a single pass.
LVR limits
The maximum LVR depends on property type and whether you'll live there. Limits are stored in Supabase and read live:
| Scenario | Max LVR | LMI triggered above |
|---|---|---|
| Owner-occupier, standard | 95% | 80% |
| Owner-occupier, new build | 95% | 80% |
| Investor | 90% | 80% |
Stamp duty: state concessions
Stamp duty brackets and concessions are read live from Supabase — they are not hardcoded. This means rate changes are reflected immediately without a code deploy. Concession types applied:
| State | FHB concession | New-build concession | OO concession |
|---|---|---|---|
| NSW | Nil ≤ $800k; tapered to $1M | None | None |
| VIC | Nil ≤ $600k; tapered to $750k | Off-plan deduction (advisory only — excluded from calc) | PPR rate ≤ $550k |
| QLD | Nil ≤ $500k; tapered to $550k | Varies — read from Supabase | None |
| WA | Nil ≤ $600k; tapered to $800k | Off-plan concession (strata only) | None |
| SA | None | Varies — read from Supabase | None |
| TAS | 50% discount (established, < $600k) | None for FHB | None |
| ACT | HBCS — full exemption (income-tested) | Varies — read from Supabase | None |
| NT | Up to $18,601 off; phaseout $500k–$650k | Varies — read from Supabase | None |
GetReal applies a 6× gross annual income DTI threshold. Here is what that figure actually is — and isn't.
What APRA actually requires
From 1 February 2026, APRA requires authorised deposit-taking institutions to limit new home loans with a DTI of 6× or above to no more than 20% of new residential lending per quarter. This is a portfolio limit on the lender, not a per-customer hard cap. There is no government rule that outright stops an individual borrower from getting a loan at DTI above 6×. If your DTI is 6× or higher, your application falls into a restricted category that the bank weighs against its internal quarterly quota.
What banks apply in practice
Rather than wait to hit APRA's 20% portfolio limit, major banks manage this internally with their own thresholds — which they don't publicly publish. Based on broker industry reporting, the broad picture as of 2026 is: ANZ applies a hard internal ceiling around 7.5×; NAB around 8×; CBA triggers tighter assessment at 6×; Westpac sends applications above 7× to manual credit review. These are operational policies, not marketing figures, and they change without notice.
Why GetReal uses 6×
Because banks don't publish their DTI limits and there is no per-customer government rule, any threshold is an estimate. GetReal uses 6× as a conservative, reasonable figure — it is the point at which APRA's portfolio pressure kicks in and at which several major lenders begin tightening their own assessment. In practice you may find a lender willing to go higher, particularly if you have a strong credit profile and low LVR. But 6× is the defensible planning assumption: it is where the system becomes visibly more restrictive, and underestimating your borrowing capacity by a small margin is safer than overestimating it.
Once the maximum loan is known, savings are applied using the same binary search as Ceiling 1 — savings cover stamp duty, registration fees, LMI, and then top up the deposit. This gives a maximum purchase price under the DTI constraint.
For buyers with no existing debt and high income, DTI rarely binds. For buyers with HECS, car loans, or existing mortgages, it often binds before serviceability does.
Serviceability answers: what is the biggest loan you can actually repay each month, after tax, living costs, and all existing commitments — even if interest rates rise 3%? This is the ceiling most people recognise from the "stress test".
The stress-test rate
APRA's Prudential Practice Guide APG 223 (August 2022) requires lenders to assess repayments at the actual loan rate plus 3 percentage points. GetReal reads the current standard variable rate from the benchmark_rates Supabase table, updated weekly from RBA data.
Monthly surplus
The maximum loan is the one where monthly repayments at the stress-test rate exactly consume the available monthly surplus:
HEM — Household Expenditure Measure
HEM is the minimum living cost floor used by lenders. GetReal uses indicative HEM benchmarks by household type (single / couple / family), number of dependants, and location (metro / regional). These are sourced from JMD Mortgages' published figures (March 2026) and stored in the hem_benchmarks Supabase table. Location is determined by postcode from the postcode_locations table, sourced from ABS ASGS Edition 3.
If your declared living expenses exceed the HEM benchmark for your household type, the higher figure is used. HEM is a floor, not a ceiling.
The tool calculates all three ceiling prices independently, then surfaces the lowest as your binding constraint. The result screen shows all three side by side so you can see exactly which one is limiting you and by how much.
For most first home buyers with moderate savings, the deposit floor is the binding ceiling. For high-income buyers with large existing debts (HECS, car loans), DTI often binds first. For buyers with variable or irregular income, serviceability tends to be the constraint.
Each ceiling also shows how your savings would be split at that price — deposit, stamp duty, LMI, and fees — so the breakdown is transparent rather than just a number.
The calculations above describe forward mode: given your savings and income, find the maximum purchase price. But the tool also runs in backward mode: you have a specific property in mind and want to know whether you can actually get there.
In backward mode you enter a target price. The tool runs the same three ceiling calculations — deposit floor, DTI, serviceability — but instead of searching for a maximum, it evaluates your position against that specific price. The result is one of three outcomes:
The gap — what would need to change?
When a ceiling falls short, the tool calculates the gap and what inputs would close it. For each failing ceiling:
| Ceiling | Gap shown | Levers to close it |
|---|---|---|
| Deposit floor | Savings gap — how much more cash is needed to cover stamp duty, LMI, registration fees, and the minimum deposit at the target price | Save more, reduce LVR target, consider a lower-cost state |
| DTI | Income gap — how much more gross annual income is needed for the 6× DTI cap to cover the implied loan at the target price. Calculated as: (target price − DTI ceiling price) ÷ 6 | Pay down HECS/car loans, increase income, find a co-borrower |
| Serviceability | Repayment gap — how much more monthly repayment capacity is needed to service the implied loan at the stress-test rate. Calculated as: (target price − serviceability ceiling price) × monthly PMT factor at stress rate | Increase income, reduce expenses, reduce existing commitments |
The binding ceiling — the one furthest from the target — is highlighted as the primary constraint. If two ceilings fail, both gaps are shown.