Home Loan Borrowing Power in Australia: How Banks Calculate What You Can Borrow

Before you start attending open houses, you need to know what you can actually borrow. Borrowing power varies by tens of thousands of dollars between lenders — and between what a bank's online calculator shows and what they'll actually approve. This guide explains exactly how Australian banks calculate borrowing capacity, what reduces it, and how to maximise your position before you apply.

How Banks Calculate Your Borrowing Power

Australian lenders don't just look at your income and multiply by a fixed number. They assess your net surplus income — the money left after all your committed expenses are deducted from your assessed income — and determine whether the new loan repayment fits within that surplus.

The formula, simplified:

The critical word in both cases is assessed — lenders apply their own methodology, not your actual figures.

How Lenders Assess Your Income

Not all income is treated the same. Here's how major Australian lenders typically treat different income types:

The 3% Assessment Rate Buffer

This is the single biggest factor most people don't know about. APRA (Australian Prudential Regulation Authority) requires lenders to assess your ability to service a loan at your actual interest rate plus 3%.

In practice: if you're applying at a 6.0% interest rate, the bank tests whether you could afford repayments at 9.0%. This dramatically reduces the amount you can borrow compared to the headline rate.

This buffer exists to protect borrowers from rate rises. It means Australians who could "technically afford" a loan at low rates are protected from over-extension if rates rise. It also means many buyers are constrained to lower loan amounts than they expect.

How Expenses Are Assessed

Lenders use a benchmark called HEM (Household Expenditure Measure) published by the Melbourne Institute. HEM represents the basic living costs for Australian households at different income levels and family compositions.

Here's what matters: lenders use the higher of HEM or your declared living expenses. If your actual expenses are unusually low, they'll use HEM anyway. This makes extreme frugality less useful for borrowing power than you might expect.

Approximate HEM benchmarks (2026):

Each additional dependant reduces your borrowing power significantly — typically by $50,000–$80,000 per child, depending on the lender and income level.

What Reduces Your Borrowing Power

These are the most common factors that reduce what a bank will lend you:

1. Existing debt commitments. Credit cards are assessed at the full credit limit, not your current balance. A $15,000 credit card limit reduces your borrowing power by approximately $50,000–$70,000 — even if the balance is zero. Cancel cards you don't use before applying.
2. Car loans and personal loans. These count as monthly commitments against your surplus income. Each $1,000/month in loan repayments reduces borrowing power by approximately $5,000–$6,000.
3. HECS-HELP debt. HECS repayments are compulsory above the repayment threshold and reduce your assessed net income. A $70,000 HECS balance at a $90,000 income means roughly $5,500/year in compulsory repayments — this counts against your borrowing capacity.
4. Buy Now Pay Later commitments. BNPL services (Afterpay, Zip, Humm) that appear on bank statements are increasingly assessed as ongoing commitments by lenders. Close unused BNPL accounts before applying.
5. Number of dependants. As shown above, each child substantially reduces HEM-adjusted borrowing capacity.
6. Self-employment income variability. If your net profit swings significantly between years, lenders use the lower year — which can dramatically reduce assessed income.

Practical Steps to Maximise Borrowing Power

These steps take time — ideally 3–6 months before you apply:

1. Pay down or close credit cards. Reduce limits to the minimum you need, or close cards entirely. This is the highest-impact single action for most borrowers.
2. Pay down personal loans and car loans. Clear short-term debt before applying wherever possible.
3. Reduce BNPL accounts. Close Afterpay, Zip, etc. if you rarely use them.
4. Demonstrate income stability. Two years in the same role (or same industry for self-employed) gives lenders maximum confidence. Avoid changing jobs in the 3 months before applying.
5. Keep bank statements clean for 3 months. Avoid large irregular withdrawals, gambling transactions, or excessive discretionary spending in the 90 days before application. Banks request 3 months of statements.
6. Apply for the right deposit size. Below 20%, you'll pay Lenders Mortgage Insurance (LMI). Above 20%, LMI is avoided and some lenders offer sharper rates. See our Mortgage Calculator to model the LMI impact.

Borrowing Power Across Income Levels

As a rough guide (assuming couple, no dependants, no existing debt, 20% deposit, 6.5% interest rate assessed at 9.5%):

These are approximate — lenders vary by 10–20% in their outcomes for the same applicant. Comparing lenders through a mortgage broker (who has access to 20–30 lenders) typically identifies the maximum borrowing amount across the market.

Pre-Approval: Why You Should Get It Before You Search

Pre-approval (also called conditional approval or approval in principle) confirms how much a specific lender will lend you based on your financials. It doesn't guarantee the loan — a full valuation and property condition assessment comes later — but it gives you a confident upper budget for your property search.

Benefits of pre-approval:

• You know your exact budget before falling in love with a property
• Agents and vendors take pre-approved buyers more seriously
• Faster settlement — much of the assessment work is already done
• Typically valid for 90 days (can be extended)

One caution: every formal credit application (including pre-approval) creates an enquiry on your credit file. Multiple pre-approval applications in a short period can reduce your credit score. Apply for pre-approval with one lender at a time, or use a mortgage broker who can obtain indicative assessments without triggering hard enquiries.

Frequently Asked Questions

How much can I borrow on a $100k salary?

As a single applicant with no dependants, no existing debt, and a clean credit history, approximately $450,000–$530,000 at current rates (2026). This varies significantly by lender. With a partner on the same income, the combined borrowing power roughly doubles.

Can I borrow more than my bank's calculator shows?

Often yes. Online calculators are conservative and don't account for lender-specific policies. A mortgage broker can identify lenders with more favourable assessment policies for your income type (e.g., lenders that treat HECS debt more generously, or credit business income more favourably).

Does borrowing power differ between banks?

Yes, materially. The same applicant can receive a borrowing limit $80,000–$150,000 higher from one major lender versus another. Lenders have different HEM benchmarks, different treatment of credit card limits, and different policies on income types. This is the primary value of using a mortgage broker.