Borrowing Power Calculator NZ
This calculator estimates how much you could borrow for a home loan in New Zealand, using the same affordability approach NZ banks apply when assessing a mortgage application. Enter your gross annual income, your partner's income if applicable, any other regular income such as rental or Working for Families, your number of dependants, estimated monthly living expenses, existing debt repayments, your chosen lender stress-test rate, and loan term. The calculator applies current NZ PAYE tax rates to find your net income, deducts your living costs and debt repayments to find your monthly surplus, then divides that surplus by the repayment required per dollar borrowed at the stress-test rate. You get your estimated maximum loan, monthly surplus, estimated monthly repayment, and the debt-to-income ratio cap of six times gross income that the Reserve Bank imposes on owner-occupier lending, plus a full breakdown of your income after tax and your expense and surplus figures showing whether affordability or the DTI cap is the binding limit on your borrowing. Adjust the stress-test rate or loan term to see how they change your result, and update the living expense figure if the auto-suggested amount does not match your actual spending. This is an indicative estimate only; each bank applies its own credit policy, expense benchmarks and lending criteria, so confirm your true borrowing capacity with a mortgage adviser or lender.
1. Income
2. Expenses and Loan Settings
Income Breakdown
Expense and Surplus Breakdown
How Borrowing Power Is Calculated in NZ
New Zealand banks use an affordability-based approach. The core formula is straightforward: your net monthly income minus estimated living expenses and existing debt repayments gives a monthly surplus. That surplus is the most you can commit to a mortgage repayment. Banks then work backwards from that surplus to find the maximum loan that the repayments would service at the stress-test rate.
The formula for the monthly repayment factor at rate r (monthly) over n months is:
Monthly repayment per dollar = r × (1 + r)^n / ((1 + r)^n − 1)
Maximum loan = Monthly surplus / Monthly repayment per dollar
Worked Example
| Step | Detail | Amount |
|---|---|---|
| Gross income | $80,000/yr single applicant | $80,000/yr |
| PAYE tax (2026/27) | $1,638 + $6,632.50 + $7,380 + $627 = $16,277.50 | -$16,277.50/yr |
| Net annual income | $80,000 - $16,277.50 | $63,722.50/yr |
| Net monthly income | $63,722.50 / 12 | $5,310/mo |
| Living expenses | Estimated (0 dependants) | -$1,800/mo |
| Existing debt repayments | Car loan etc. | -$500/mo |
| Monthly surplus | $3,010/mo | |
| Stress-test rate | 8.5% pa, 30 years | r = 0.085/12 |
| Repayment factor | r(1+r)^360 / ((1+r)^360 - 1) | $769 per $100k/mo |
| Maximum loan (affordability) | $3,010 / 0.007691 | ~$391,000 |
| DTI cap (6x gross) | $80,000 x 6 | $480,000 |
| Binding estimate | Lower of the two | ~$391,000 |
NZ PAYE Tax Rates (2026/27)
| Taxable Income Band | Rate |
|---|---|
| $0 to $15,600 | 10.5% |
| $15,601 to $53,500 | 17.5% |
| $53,501 to $78,100 | 30% |
| $78,101 to $180,000 | 33% |
| Over $180,000 | 39% |
The calculator applies these bands to gross income for each applicant. KiwiSaver contributions and the ACC earners levy are not deducted in this estimate; including them would reduce your take-home pay by approximately 3.5 to 5.5% further.
What Is a Stress-Test Rate?
NZ banks do not assess your ability to service a mortgage at the rate you will actually pay. Instead they use a higher test rate, typically 1.5 to 2 percentage points above the lowest current floating rate, to ensure you could still meet repayments if interest rates rise. In 2026 most major NZ banks apply a stress-test rate of approximately 8.0% to 9.0%. This means your assessed maximum loan will be lower than if the bank simply used the current one-year or two-year fixed rate.
The Debt-to-Income (DTI) Cap
Since June 2024, the Reserve Bank of New Zealand has allowed banks to lend no more than 6 times gross annual income to owner-occupiers (and 7 times for investors) under its DTI speed limits. This cap applies to total debt, so if you already have personal loans or credit card balances the amount available for a home loan may be reduced further. The calculator shows the DTI cap alongside the affordability-based estimate and flags whichever is the binding constraint.
Living Expense Benchmarks
Banks use the Household Expenditure Measure (HEM) as a minimum when assessing living costs. If your stated expenses are below HEM, the bank will substitute HEM automatically. Approximate monthly HEM benchmarks used in NZ:
- Single applicant, no dependants: approximately $1,600 to $1,900/month
- Couple, no dependants: approximately $2,200 to $2,600/month
- Each additional dependant: approximately $300 to $500/month extra
The calculator auto-suggests a living expense figure based on your household size; you can override it to reflect your actual spending.
Tips to Increase Your Borrowing Power
- Pay off short-term debt: Every dollar of monthly debt repayment you eliminate translates to roughly $130 more borrowing capacity at 8.5% over 30 years.
- Reduce credit card limits: Banks count your credit card limit (not balance) as potential debt. Halving a $10,000 limit can add $50,000 or more to your assessed loan ceiling.
- Add a co-borrower: A partner's income can substantially increase the combined surplus available for repayments.
- Increase your deposit: A larger deposit reduces the loan needed, which may bring you within the 80% LVR threshold and avoid the low-equity premium.
- Boost income: Overtime, rental income, and Work and Income Family Tax Credit are accepted by most banks if they are regular and documented.
Related Calculators
- Mortgage Calculators: hub for all NZ mortgage and home loan tools.
- Mortgage Repayment Calculator: calculate your regular repayment on a given loan amount.
- Borrowing Capacity Calculator: detailed LVR-based borrowing capacity tool.
- Mortgage Stress Test Calculator: test whether you can afford your loan if rates rise.
- Deposit Gap Calculator: work out how long until you have enough deposit.
Sources and method: NZ PAYE tax rates from Inland Revenue (ird.govt.nz, income tax rates 2026/27). Reserve Bank of New Zealand DTI policy (rbnz.govt.nz, debt-to-income ratio restrictions). Bank affordability assessment methodology based on publicly available CCCFA guidance and major NZ bank home loan documents. Stress-test rates are indicative of typical practice in mid-2026; individual banks set their own floors.
This calculator provides a general estimate only and does not constitute financial advice. Actual borrowing limits depend on your full credit profile, the bank's internal policy, and the specific loan product. Consult a registered mortgage adviser or your bank for a precise pre-approval assessment.