Mortgage Stress Tests in NZ: What Banks Look For and How to Prepare

What a mortgage stress test is

A mortgage stress test is an affordability assessment run at a higher interest rate than the actual rate you'll pay. The idea is to check whether you could still service the loan if rates increased significantly after you borrowed. Rather than asking "can you afford repayments at today's rate?", the bank asks "can you afford repayments if rates jump to 8.5% or 9%?".

This matters because mortgages are long-term commitments. Someone who borrows at 5.5% today might still be paying the loan in 10 years when rates are very different. If the bank only assesses affordability at 5.5%, they're not accounting for the real risk that rates could rise substantially during the loan term.

What test rates do NZ banks actually use?

Each bank sets its own stress test rate, but they generally cluster between 8.5% and 9.5% for residential lending. This figure doesn't move directly with the OCR (Official Cash Rate) — banks update it periodically based on their view of where rates might realistically go over a mortgage term. During the period when the OCR was near zero (2020–2021), stress test rates remained around 6–7%. When rates rose sharply from 2022 onward, some banks increased their test rates to 9% and above.

Importantly, you can't negotiate the test rate. It's a bank policy figure. What you can influence is your income, your debt load and your expenses — the inputs the bank uses alongside the rate.

The real-world impact on borrowing power

The test rate has a dramatic effect on how much you can borrow. Consider a couple with $150,000 combined gross income, no debts, no dependants and a 20% deposit. At an actual mortgage rate of 5.5%, their repayments on a $750,000 loan over 30 years would be around $4,258 per month. That's manageable against their income.

But the bank tests at 9%. At 9%, repayments on that same $750,000 jump to about $6,035 per month. The bank now needs to confirm this couple can meet $6,035 in repayments plus living costs from their after-tax income — and if the numbers don't stack up, the approved loan comes down until they do. Many couples in this situation find their approved amount is $550,000–$650,000 rather than the $750,000 they expected.

This gap — between what you expect to qualify for at the advertised rate and what you actually qualify for at the stress test rate — is one of the most common shocks in the home buying process. Running your own stress test before you apply removes that shock.

How banks assess "living expenses" under CCCFA

Since amendments to the CCCFA came into effect, banks are required to assess actual living expenses — not just apply a generic household expenditure benchmark. In practice this means the bank looks at your recent bank statements (typically 3 months) to understand your actual spending patterns.

This created significant friction when the rules first came in (2021–2022), with banks declining applications based on expenses like Netflix subscriptions or restaurant spending. The rules were subsequently loosened, but banks still do a more thorough expense check than they did pre-2021. One-off large expenses that appear in your statements (a holiday, a vehicle purchase) can be explained as non-recurring, but consistent high discretionary spending can affect the assessment.

Knowing this is coming, it makes sense to review three months of statements before applying and understand what the bank will see — not to manipulate the picture, but to be ready to explain anything that looks like an outlier.

Running your own stress test

You don't need to wait for the bank to apply a stress test to your application. You can run it yourself in a few minutes.

Take your expected mortgage amount and calculate monthly repayments at 9% (or whatever you think your bank's test rate is). Then look at your actual after-tax monthly income and subtract your living costs (based on your real monthly spending). The remaining surplus needs to comfortably cover those stress-tested repayments.

If it doesn't — if the stress-tested repayment amount exceeds what you have available after living costs — you're likely to be declined or offered a lower loan amount. Better to know that now than after you've paid for a building report and submitted a formal application.

The Interest Rate Stress Test calculator on HomeCalcs lets you input your loan balance and see the repayment at any rate you specify — useful for modelling both your current actual rate and the bank's test rate side by side.

What you can do if the stress test is limiting you

If running the numbers suggests the stress test will cap your borrowing below what you need, a few things can help:

• Reduce existing debt first. Every dollar of existing debt repayment reduces the income available to service the mortgage in the bank's model. Eliminating a car loan or personal loan before applying can meaningfully shift the result.
• Increase your deposit to reduce the loan amount. A larger deposit means a smaller loan, which means the stress-tested repayment is lower. Even a modest increase in deposit can bring the loan within serviceable range.
• Add a co-borrower. A second income on the application increases the income base the bank uses. This is common for couples where both partners are borrowing, but some people also use family members as co-borrowers — which has legal implications worth understanding before proceeding.
• Consider a different lender. Banks do vary in their test rates and expense assessment methodologies. A mortgage adviser can compare which lender's model works best for your specific situation.
• Revisit your target price. Sometimes the honest answer is that the loan amount you need to purchase at your target price doesn't clear the stress test, and adjusting your price target is the right answer.

A stress test for existing borrowers too

Stress testing isn't just for people applying for new mortgages. If you already have a mortgage, it's worth periodically stress-testing your own situation: what would your repayments be at 9%? Could you cover that from your current income? If not, how much of a buffer do you have before you'd need to make changes?

This exercise is particularly relevant when refixing. If you've been on a low fixed rate and your next refix is coming up, the actual new rate may be significantly higher than what you've been paying. Running the numbers before your refix date — rather than discovering the new repayment on your first statement — gives you time to adjust spending or make a lump sum payment before the higher rate kicks in.

These calculations are for guidance only and do not constitute financial advice. Bank stress test rates and CCCFA assessment criteria change over time. Always speak with a qualified mortgage adviser or your lender about your specific situation.