How Banks Calculate How Much You Can Borrow?
Your income matters—but it is only one part of the calculation. Here is what banks actually assess when working out your home-loan borrowing power.
Buying a home often begins with one important question: “How much can I actually borrow?”
It may be tempting to multiply your income by a certain number or rely on an online calculator. However, banks use a more detailed assessment. They consider your income, regular expenses, debts, deposit, credit history, dependants and ability to continue making repayments if interest rates increase.
Two people earning exactly the same income can receive very different lending results. Their expenses, credit limits, dependants, deposit and financial commitments can change the outcome.
What is borrowing power?
Borrowing power is the estimated maximum amount a lender may be prepared to lend based on your financial position. Banks generally assess two separate questions:
- Can you afford the loan repayments?
- Does the property provide enough security for the loan?
Passing one assessment does not automatically mean you will pass the other. You may have enough income to service a particular mortgage but not enough deposit for the intended purchase—or a substantial deposit but insufficient income to support the repayments.
1. Your income
Income is the starting point of the bank’s calculation. Depending on the lender and the evidence available, banks may consider salary or wages, self-employed income, overtime, allowances, commission, bonuses, rental income, boarder income, government payments and investment income.
Gross income versus usable income
Your gross income is what you earn before tax. The bank’s affordability calculation, however, considers the income available after tax and other deductions. A lender may also discount income that is irregular, temporary, difficult to verify or unlikely to continue throughout the loan term.
If you are self-employed, the bank may review financial statements and tax returns and could average your income across more than one financial year. Variable overtime, commission and bonuses may also be averaged rather than accepted at their highest recent level.
2. Your existing debts and credit limits
Banks assess your total debt position, not only the mortgage you are applying for. The assessment can include personal loans, car finance, credit cards, buy now pay later accounts, student loans, overdrafts, hire purchase and existing mortgages.
Even if a credit card has a low balance, its full limit may still reduce borrowing power because the available limit represents potential future debt. Closing genuinely unused facilities or reducing unnecessary limits may help, but changes should be considered before an application is submitted.
3. Your regular living expenses
The bank needs to see that you can make mortgage repayments and still have enough money to live on. It may review groceries, utilities, insurance, transport, childcare, education, subscriptions, healthcare, rates, maintenance and other recurring commitments.
Lenders can compare the expenses you declare with your transaction history and their own household-expense benchmarks. A realistic budget is more useful than entering unusually low figures that are not supported by your bank statements.
4. The bank’s test interest rate
The advertised mortgage rate is not necessarily the rate used to assess your application. A bank may calculate your proposed repayments using a higher assessment or test rate to check whether you could manage if interest rates increased.
Because each lender has its own servicing model and assessment rate, the same household may receive different borrowing estimates from different banks.
5. Your available surplus
After calculating usable income, household expenses, existing commitments and tested mortgage repayments, the lender looks at the amount remaining. This may be described as your servicing surplus or uncommitted monthly income.
Usable income − living expenses − existing debts − tested mortgage repayments = available surplus
A stronger surplus suggests that your household has more capacity to manage unexpected costs or future changes in interest rates.
6. Your debt-to-income ratio
Your debt-to-income ratio, or DTI, compares your total debt with your annual gross income.
Total debt ÷ annual gross income = DTI ratio
For example, if a household earns $120,000 before tax and would have total debt of $600,000, its DTI ratio is 5.
Under current Reserve Bank settings, owner-occupier borrowing above six times gross annual income is considered high-DTI, while investor borrowing above seven times gross annual income is considered high-DTI. Banks can still make a limited proportion of lending above those thresholds, and their own affordability rules continue to apply.
7. Your deposit and loan-to-value ratio
Your deposit affects how much the lender is being asked to advance against the property. The loan-to-value ratio, or LVR, compares the mortgage amount with the property’s value.
Mortgage amount ÷ property value × 100 = LVR
A smaller deposit creates a higher LVR and generally increases the lender’s risk. Low-deposit lending may involve stricter affordability requirements, low-equity pricing or additional conditions.
Current Reserve Bank settings allow banks to allocate up to 25% of new owner-occupier lending above 80% LVR and up to 10% of new investor lending above 70% LVR. These are portfolio-level limits for banks, not automatic approval thresholds for individual applicants.
8. Your credit history and account conduct
Banks may review missed payments, defaults, debt collection, frequent overdraft use, dishonoured payments, payday lending, recent credit applications and whether your accounts generally remain within their limits.
A past issue does not always mean an automatic decline, but the lender may request an explanation and evidence showing that the problem has been resolved.
9. Your household and dependants
A household with children will normally be assessed as having higher living costs than a household with no dependants. The lender may consider childcare, school expenses, parental leave, child-support obligations and whether another adult depends financially on the applicants.
10. Your proposed loan term
A longer loan term can reduce the calculated regular repayment and may improve servicing capacity. However, it usually means paying more interest over the life of the loan. The lender may also consider your age, expected retirement date and how any debt extending into retirement would be repaid.
Why different banks give different answers
There is no single borrowing-power calculation used by every New Zealand bank. Lenders may differ in their treatment of overtime, bonuses, self-employed income, rental income, boarder income, credit limits, household expenses, test rates and required servicing surplus.
A decline from one lender does not necessarily mean every bank will reach the same result. However, making several applications without a clear strategy can create unnecessary credit enquiries.
A simple borrowing-power example
Consider a couple earning a combined gross income of $145,000. They have a $20,000 car loan, a credit card with a $10,000 limit, one child, a $120,000 deposit and regular childcare expenses.
Income $145,000 gross household income
Deposit $120,000 available
Existing commitments Car loan and credit-card limit
Household factors One child and childcare expenses
The lender will assess usable income, existing repayments, the credit-card commitment, household expenses, proposed mortgage repayments at its test rate, the resulting surplus, total DTI, proposed LVR and the applicants’ credit history before estimating a suitable loan amount.
How to improve your borrowing power
Depending on your circumstances, useful steps may include:
- Repaying or reducing short-term debts
- Lowering unnecessary credit-card limits
- Closing unused buy now pay later accounts
- Building a larger deposit
- Maintaining stable employment and income
- Keeping self-employed financial records current
- Correcting errors on your credit report
- Avoiding unnecessary new credit applications
The maximum amount a bank is willing to lend is not necessarily the amount your household should borrow. Your own comfort level and future plans matter too.
Online calculators versus a complete assessment
An online calculator can provide a useful starting point, but it may not fully account for irregular income, complex self-employment, multiple properties, credit issues, lender-specific expense benchmarks or changing bank policy.
A personalised assessment can provide a more realistic picture before you begin making offers on properties.
Find out what you may be able to borrow
A mortgage adviser can review your income, expenses, deposit and debts, explain possible limitations and compare relevant lender policies.
Frequently asked questions
- How many times my income can I borrow?
There is no guaranteed income multiple. DTI restrictions, affordability testing, your expenses, existing debts, deposit and lender policy all affect the result.
2.Does a credit-card limit affect borrowing power?
It can. A lender may assess the available limit as a potential financial commitment even when the current balance is low.
3.Does a bigger deposit increase borrowing power?
A larger deposit lowers your LVR and can provide access to more lending options, but you must still demonstrate that you can afford the repayments.
4.Why is the bank’s estimate lower than an online calculator?
The bank may use a higher test rate, minimum household-expense benchmarks and stricter treatment of variable income, credit limits and existing debts.
5.Can two banks offer different loan amounts?
Yes. Banks can use different assessment rates, expense assumptions, income policies and servicing models.
