Beginner's Guide to Calculating Borrowing Capacity

How Lenders Calculate What You Can Borrow

Lenders assess your borrowing capacity by looking at your income, your existing debts, and your living expenses, then apply a buffer to ensure you can still afford repayments if rates rise. Most lenders add a buffer of around 3% to the current interest rate when testing your ability to service a loan, which means they're checking whether you could still manage repayments at a rate higher than what you'd actually pay today.

The calculation starts with your gross income. If you're buying together, both incomes are combined. Lenders then subtract your monthly commitments such as credit card limits, personal loans, car finance, and HECS-HELP debts. They also deduct an estimate of your living expenses, which can be based on either your actual spending or a benchmark figure called the Household Expenditure Measure (HEM). The amount left over determines how much you can afford in monthly repayments, which translates into a maximum loan amount.

Consider a couple earning a combined income of $140,000 per year who have no other debts and relatively modest living expenses. At current variable rates with a 3% buffer applied, they might qualify for a loan between $600,000 and $700,000 depending on the lender's assessment policies. That same couple with a $20,000 car loan and two credit cards with $15,000 combined limits might see their capacity drop by $100,000 or more, even if the cards carry no balance.

Why Two Incomes Don't Always Double Your Capacity

Combining incomes increases what you can borrow, but not always in a straight line. Lenders apply different treatment to different income types, and some will shade or discount certain earnings when calculating serviceability.

Full-time salary income is generally assessed at 100% of its value. Casual or variable income, overtime, and bonuses are often shaded, meaning lenders might only count 80% of that income, or they might average it over two years and then apply a discount. If one partner earns $70,000 as a base salary and the other earns $50,000 with $10,000 in overtime, the lender might assess the combined income at closer to $125,000 rather than $130,000.

This shading becomes more pronounced when one or both buyers are self-employed, on probation, or working part-time. In our experience, couples often overestimate their capacity when one income is less stable, which can lead to disappointment when they've already found a property they want to buy. Running a borrowing capacity calculation with accurate income details before you start searching saves time and frustration.

The Impact of Existing Debts on What You Can Borrow

Every ongoing commitment reduces your borrowing capacity, but not all debts are treated the same way. Credit cards are assessed based on their limit, not the balance you're carrying. A card with a $10,000 limit and zero balance will reduce your capacity by roughly the same amount as one with a $10,000 balance, because lenders assume you could max it out at any time.

Personal loans, car loans, and buy-now-pay-later accounts are assessed based on their minimum monthly repayment. HECS-HELP debts don't have a monthly repayment in the traditional sense, but they reduce your net income once you hit the compulsory repayment threshold, which means lenders factor them in as a reduction to your available income.

In a scenario where a couple has a combined income of $130,000, a car loan with $400 monthly repayments, and two credit cards with a combined limit of $20,000, their borrowing capacity could be $80,000 to $120,000 lower than if they had no debts at all. Closing unused credit cards and paying off smaller debts before applying for pre-approval can make a material difference to what you're able to borrow.

How Living Expenses Are Assessed and Where You Have Control

Lenders use one of two methods to assess your living expenses: they either rely on your declared expenses, or they apply a benchmark figure based on your household size and income level. The Household Expenditure Measure is updated quarterly and varies depending on how many people are in your household and where you sit on the income spectrum.

If your actual expenses are lower than the HEM benchmark, most lenders will use the higher figure anyway. If your declared expenses are higher than HEM, they'll use your declared figure. That means inflating your expenses won't reduce your capacity unless you're genuinely spending more than the benchmark, but understating them won't help you either.

Where you do have control is in reducing discretionary spending in the months leading up to your application. Lenders will review your bank statements, and patterns of high spending on dining, entertainment, or gambling can raise concerns about your ability to manage a mortgage. Trimming back these expenses for three to six months before you apply demonstrates financial discipline and improves your serviceability on paper.

How Interest Rate Buffers Affect Your Maximum Loan Amount

Lenders don't assess your borrowing capacity at the actual rate you'll pay. They add a buffer, typically around 3%, to account for potential rate rises over the life of your loan. This means if you're looking at a variable rate of 6.5%, the lender will test whether you can still afford repayments at 9.5%.

The size of this buffer varies slightly between lenders, and some apply a minimum floor rate regardless of where the market sits. If the variable rate drops to 5%, a lender with a 3% buffer and a 7.5% floor rate will still test you at 7.5%, not 8%. This floor rate can benefit borrowers when rates are low, but it also limits how much extra capacity you gain when rates fall.

For first home buyers, this buffer often feels punishing because it restricts how much you can borrow even though you're confident you could afford higher repayments at today's rate. The buffer exists to protect both you and the lender from a situation where rising rates push your repayments beyond what you can manage, but it does mean your borrowing capacity is lower than what the advertised rate alone would suggest.

Lender Policy Differences and Why Capacity Varies Between Banks

Not all lenders assess borrowing capacity the same way. Some are more generous with how they treat certain income types, while others have stricter expense benchmarks or apply higher buffers. A couple might be offered $650,000 from one lender and $720,000 from another, even though they've provided identical information.

These differences come down to internal policy settings. Some lenders will accept 100% of bonus income if it's been consistent for two years, while others cap it at 50%. Some assess rental income from an investment property at 80% of the lease amount to account for vacancies and maintenance, while others use 100% if you can demonstrate strong tenancy history. Lenders also differ in how they treat childcare costs, private school fees, and other non-discretionary expenses.

This variation is one reason working with a mortgage broker makes sense when you're trying to maximise what you can borrow. We regularly see situations where a couple has been knocked back by their own bank, only to be approved by a different lender for the amount they need. Shopping your application across multiple lenders without guidance can hurt your credit file, but a broker can identify which lenders are likely to give you the strongest outcome before any formal applications are lodged.

Improving Your Capacity Before You Apply

If your borrowing capacity falls short of what you need, there are practical steps you can take in the months before you apply. Paying down or closing credit cards is one of the fastest ways to lift your capacity. Consolidating multiple debts into a single personal loan can also help, particularly if the combined minimum repayments are high.

Increasing your income is effective but not always realistic in the short term. If you're expecting a pay rise, a promotion, or the end of a probation period, it may be worth waiting until that change is reflected in your payslips before applying. Lenders typically want to see at least one or two payslips showing the new income before they'll assess it.

Reducing your living expenses won't help if you're already below the HEM benchmark, but demonstrating lower discretionary spending on your bank statements can improve how lenders view your application. If you're self-employed, lodging your most recent tax return and ensuring your financials are up to date can prevent delays and ensure your income is assessed at its full value. If you're planning to apply with a guarantor, their income and property equity can also increase what you're able to borrow without needing to improve your own financial position first.

Call one of our team or book an appointment at a time that works for you. We'll run a detailed capacity assessment across multiple lenders and help you understand what you can borrow and what steps, if any, might increase that figure before you start searching for a property.

Frequently Asked Questions