How Banks Calculate Your Borrowing Capacity (HEM Explained)

Three banks, three calculators, three different answers. On the same income, same debts and same postcode, the gap between them can top $150,000. That's not a rounding error; it's the difference between the suburb you want and the one you settle for.

The reason is simple. Your borrowing capacity isn't one number. It's 45 or more numbers, one per lender, and any single bank's borrowing capacity calculator shows you exactly one of them. Understanding how banks assess capacity, and where each lender bends, is how you find the highest of those numbers instead of the first one Google served up.

The timing matters too. After three RBA hikes in the first half of 2026, the cash rate sits at 4.35%, and APRA confirmed on 28 May 2026 that the 3% serviceability buffer stays put. Assessments are tighter than they were a year ago. But a rising-rate market is a quieter one: auction clearance rates in the low 40s (Cotality, June 2026) mean fewer rival bidders. Buyers who know their real capacity now are negotiating while the crowd waits for the cycle to turn.

What actually goes into a borrowing capacity calculation?

Four inputs decide your number: income, expenses, existing debts, and the rate your repayments are tested at. Each one hides a surprise.

Same borrower, four judgement calls, and each lender makes them differently. That's the whole story of why capacity varies so much across the market, and why the rest of this article walks through the three inputs that move the number most.

What is HEM, and why doesn't your budgeting move it?

HEM is the Household Expenditure Measure. The Melbourne Institute builds it from ABS household spending data, and it estimates what a household like yours spends each month, scaled by income, postcode and dependants. When you declare your living expenses, the lender uses your figure or HEM, whichever is higher.

That comparison flips the usual advice on its head. You've probably been told to cancel the streaming services and eat at home for three months before applying. For most borrowers, that ritual changes nothing: if your declared spending already sits below the HEM floor for your income band, the lender substitutes HEM anyway. Your frugal quarter never enters the maths.

What does move the number is structural, not behavioural. Close the unused credit card. Clear the car loan four months early. Those change the debt inputs, which no benchmark overrides. We've watched an untouched $12,000 credit card limit strip roughly $50,000 from an approval; the balance was zero, and the limit alone was the problem.

There's a second trap on the other side. Declare expenses well above HEM (private school fees are the classic) and lenders will use your higher figure. HEM is a floor, not a ceiling.

Why do banks test you at 3% above your actual rate?

Because APRA tells them to. Every new loan is assessed as if your rate were 3 percentage points higher than the one you'll actually pay, a buffer APRA reviewed and held on 28 May 2026 despite the 2026 rate rises.

Chain that through. Rates rose across February, March and May 2026, so the buffered assessment rate rose with them, so the same salary supports a smaller loan than it did in late 2025. For buyers, that means your pre-approval from last spring is probably stale. For refinancers, it explains the strange trap where a new lender declines you for a repayment smaller than the one you're already making: you're free to leave your current bank, but the new lender's buffered assessment has to say yes first. We've unpacked the mechanics in our serviceability buffer guide.

Equity is the other half of that refinance test. If your loan sits above 80% of your property's value, most lenders add LMI or decline outright (see how LVR works). Under specialist lending policies available through Wity, any borrower can refinance at up to 85% LVR with no LMI, rising to 90% for nurses, midwives, allied health and senior professionals, and 95% for doctors and dentists.

Do the new DTI caps change how much you can borrow?

For some borrowers, yes, and 2026 is the first time this lever has been pulled. Since 1 February 2026, APRA caps the share of each lender's new owner-occupier and investor loans written at a debt-to-income ratio of six or higher: no more than 20% of the book. Construction loans and new builds are exempt.

A cap on the lender's book isn't a ban on you. But it means high-DTI approvals are now rationed. A lender that's already brushing its 20% quota this quarter will decline a DTI-6.2 application that a rival with headroom would approve next week. Your file didn't change; the lender's dashboard did. Timing and lender selection now matter as much as the application itself, which is a strange thing to say about a regulation, and exactly why a one-bank calculator can't see it. Our debt-to-income ratio explainer covers how to find your own multiple.

Can your HELP debt stop counting against you?

HELP debt got two boosts recently. The 20% balance cut legislated in August 2025 shrank the debt itself, and the repayment threshold sits at $69,528 for 2026-27 with marginal rates of 15c per dollar above it, so lower earners keep more income in the assessment.

The bigger shift is newer. Since 30 September 2025, lenders have been allowed to exclude a HELP debt from serviceability entirely if it's within roughly 12 months of being cleared. CBA reported eligible borrowers gained around 21% in borrowing capacity from that change alone. If your balance is small, the order of operations flips: clearing (or nearly clearing) it before applying can add six figures to your capacity, where a year ago it barely registered.

Doctors and dentists get further still: under our medico policy, HECS/HELP is excluded from capacity calculations regardless of the balance. The full detail is in our HECS and borrowing power guide.

Why one borrowing capacity calculator can undersell you by six figures

Put the pieces together and the spread between lenders stops being mysterious. One shades overtime to 80%, another takes 90%. One applies HEM bluntly, another interrogates your actual statements. One excludes your near-dead HELP debt, another counts it to the last dollar.

Take Sonia, a construction project manager in Parramatta earning $128,000 with no dependants. She has $6,000 left on her HELP debt after the 20% cut, plus that unused $12,000 credit card.

At the first bank's calculator: card limit assessed at about $450 a month, HELP repayments counted, overtime shaded. Capacity: roughly $605,000.

Structured properly: card closed before applying, HELP excluded because it clears within 12 months, application placed with a lender that accepts more of her overtime. Capacity: closer to $700,000, at a DTI still under six, so the new caps don't bite.

The gap: roughly $95,000, on identical income, from decisions made before the application went in.

Based on typical scenarios. Individual outcomes vary.

That second path is what the Wity Borrowing Power Assessment does. It models your capacity across 45+ lenders, not one bank's calculator, and shows which lender treats your overtime, your card limits and your HELP balance most generously, before you apply anywhere and while your credit file stays untouched.

What should you do this month?

Three moves, in order. Close or cut credit limits you don't use. Check your HELP balance against the 12-month clearance rule before deciding whether to pay it down. Then get your capacity modelled across the whole market rather than one bank's website, because the highest of your 45 numbers is the only one that matters on auction day.

Want your real number, not the calculator's guess? Start the Wity questionnaire → Free, no credit check, two minutes.