A quick heads-up: The information and interactive RBNZ data in this article are designed as a general educational guide only and do not constitute personalised financial, tax, or legal advice. Because everyone's lending structure is different, speak with a registered Financial Adviser before locking in a mortgage strategy. For full transparency on how we are paid by lenders, see How We Get Paid.
A Debt-to-Income (DTI) ratio is a Reserve Bank of New Zealand (RBNZ) lending rule that limits how much total debt you can hold compared to your before-tax household income. Under current settings, most home buyers (owner-occupiers) can borrow up to 6 times their gross annual income, while property investors can borrow up to 7 times their gross annual income. Banks can still make a limited amount of lending above those thresholds under the RBNZ's 20% speed limits.
When DTI rules were first activated in July 2024, many Kiwis worried it would lock them out of buying a home. In reality, DTI restrictions currently do not affect the vast majority of everyday home buyers.
Why haven't DTI rules dominated the headlines until recently? Because every mortgage application has to pass two tests: the Reserve Bank's DTI Threshold (6x or 7x) and the bank's internal stress-test rate (currently ~6.85% to 7.20%). At a ~7.00% test rate over a 30-year term, a household with no secondary debts and one child can typically service a loan of right around 6 times their income.
That means today's market sits right at the tipping point: if you have student loans, credit cards, or multiple dependants, the bank's monthly budget calculator will usually stop you around 4.8x to 5.5x income before DTI ever matters. But if you have clean accounts, strong income, or if bank test rates drop even slightly below 7%, you will likely bump straight into the 6x (or 7x) DTI ceiling.
How Does a Bank Calculate Your DTI?
The maths behind a DTI ratio is much simpler than a bank's monthly budget calculator. The bank divides your total debt and credit limits by your total gross (before-tax) annual income:
What Counts Towards Your Debt?
A common trap is thinking DTI only looks at your new mortgage. Under RBNZ DTI rules, banks must include all personal debt and available credit limits across your household:
- All mortgages: The new home loan you are applying for, plus any existing owner-occupied or rental loans.
- Credit cards and overdrafts: Counted at their maximum limit, not what you owe today. As we cover in our guide on how a $10,000 credit card limit silently reduces your borrowing power, a $10,000 card with a $0 balance still adds $10,000 to your DTI debt pile. Β
- Buy Now, Pay Later (BNPL): Account limits with Afterpay, Zip, and Klarna are counted in full (read more on how Afterpay and BNPL schemes affect your mortgage). Β
- Student loans: Your total remaining student loan balance with Inland Revenue (IRD) is included.
- Personal and car loans: Any hire purchases, car finance, or business debts you personally guarantee.
What Counts Towards Your Income?
Banks combine your verifiable gross annual income (before tax):
- Base salary or wages, plus regular overtime, bonuses, and commission. Β
- Self-employed net profit (often averaged over two years, though some banks accept 1 year of business financials). Β
- Gross rental income from existing or proposed investment properties. Β
- Flatmate or boarder income (within the bank's policy guidelines). Β
Why Were DTIs Brought In If They Don't Bite Today?
It is fair to ask: if bank affordability calculators already stop most buyers around 5x their income, why did the Reserve Bank introduce a 6x and 7x speed limit?
The answer goes back to 2020 and 2021. During the pandemic, fixed mortgage rates dropped to historic lows of around 2.19% to 2.50%, and bank stress-test rates fell to roughly 5.50%. Because monthly repayments were so low at those rates, standard bank calculators allowed households to borrow 8, 9, or even 10 times their income. When inflation spiked and interest rates climbed back toward 7% in 2023β2024, borrowers with high debt multiples faced severe mortgage stress.
Alongside Loan-to-Value Ratio (LVR) restrictions, the Reserve Bank designed DTIs as a permanent safety guardrail for future low-interest-rate cycles. By switching DTIs on while interest rates were high enough that the rules wouldn't shock the market, the RBNZ ensured that if mortgage rates ever drop into the 3% range again, household debt won't spiral out of control.
Who Actually Gets Affected by DTI Right Now?
Even though most first-home buyers and movers won't hit the DTI ceiling at today's interest rates, four groups of borrowers can still run into DTI limits right now:
- Property Investors Growing a Portfolio: Investors have a 7x DTI threshold, which sounds higher than 6x. However, when you use your home's usable equity to buy an investment property (or keep your first home as a rental when upgrading), your total mortgage debt grows much faster than your gross rent. For example, a $700,000 rental earning $35,000 a year in gross rent has a standalone DTI of 20x ($700,000 Γ· $35,000). Across two or three rentals, that quickly uses up your personal salary buffer and hits the 7x limitβeven if your investment property cash flow works on paper. Β
- High-Income Households with Low Expenses: Basic living costs (food, power, petrol) don't double just because your salary doubles. Households earning $250,000 to $350,000+ with no dependents often have huge monthly surpluses. A bank's affordability calculator might say they can afford a loan at 6.4x their income, meaning the 6x DTI rule steps in to limit the loan.
- Borrowers with Large Student Loans & Unused Credit Cards: Because student loans and undrawn credit card limits count dollar-for-dollar toward your total debt, a graduate couple with $70,000 in combined student loans and $15,000 in credit card limits loses $85,000 off their DTI ceiling before they even start house hunting.
What Is Exempt from DTI Restrictions and What Are the Exceptions?
The Reserve Bank's DTI framework includes important exemptions so that new housing supply and sensible refinancing aren't blocked. You are not restricted by the 6x or 7x DTI threshold in the following situations:
- New Builds and Construction Loans (100% Exempt): To support new housing supply in New Zealand, borrowing via a construction loan with progress payments or buying a turnkey new build off the plan (purchased directly from the developer within 6 months of code compliance) is completely exempt from both DTI rules and LVR deposit restrictions. You can compare both pathways using our Turnkey vs. Construction Loan Calculator, or read more on how new build vs. existing property investments stack up. Β
- The 20% Bank "Speed Limit" Allowance: Banks are allowed to approve up to 20% of their new owner-occupier lending above 6x DTI, and 20% of their new investor lending above 7x DTI. Because only 9.1% of first-home buyer loans are currently over 6x DTI, banks currently have some room in their exemption buckets for strong applicants with good deposits. Β
- Dollar-for-Dollar Refinancing: Switching your mortgage from one bank to another to get a better interest rate or home loan cashback is exempt from DTI rules, provided you aren't increasing your total loan balance. Check if switching makes sense for you with our Refinance Calculator. Β
- KΔinga Ora First Home Loans: Low-deposit loans underwritten through the KΔinga Ora First Home Loan scheme (see our Complete Guide to the KΔinga Ora First Home Loan) are exempt from RBNZ DTI limits. Β
- Bridging Finance & Property Remediation: Short-term bridging finance (while you transition between homesβestimate your numbers with our Net Proceeds Next Home Calculator) and loans for essential weather-tightness or earthquake repairs are also exempt. Β
- Non-Bank Lenders: Non-bank lenders (such as Liberty, Resimac, or Pepper Money) are not registered banks and are not bound by RBNZ DTI rules, making them a practical stepping-stone option for self-employed borrowers or property investors who need extra flexibility.
Check Your Numbers: Interactive DTI & Affordability Calculator
Want to see your own DTI ratio and whether you are more likely to be limited by the bank's stress-test rate or the Reserve Bank's DTI rule? Use our interactive calculator below, or dive deeper with our full Borrowing Power Calculator and Home Loan Repayment Calculator. Β
Ready to Find Out Your True Borrowing Power?
Online calculators and Reserve Bank acronyms only tell half the story. Every New Zealand bank calculates living costs, overtime and bonuses, boarder income, and stress-test rates slightly differently,and knowing which bank has the most generous policy (or open DTI speed-limit space) can easily make a $50,000 to $100,000+ difference to your pre-approval. Β At Home Loan Factory, our team of expert mortgage advisers does the heavy lifting across the banks and specialist lenders for you. See how we are paid here. Β
Start your conversation with a Home Loan Factory Adviser Today β Β
Try Our Full NZ Borrowing Power Calculator β
β
