The Stress Test: Why the Bank Tests You at ~7% When Current Rates Are Lower

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When a New Zealand bank assesses your mortgage application, they do not calculate your borrowing power using the interest rate you see advertised on TV or the internet. Instead, they run your application through a "Servicing Test Rate."

It can feel incredibly frustrating to be rejected based on an interest rate you won't actually be paying.  

Here is a straightforward, jargon-free look at why banks use the stress test, and the hidden catch regarding how they calculate your everyday expenses.

Why banks test your mortgage at a much higher rate

It is easy to look at a 7% test rate and assume the bank is just being unnecessarily strict. However, lenders have three very specific reasons for testing your application with a heavy buffer.

1. The 30-year reality of fluctuating rates

A mortgage is a 30-year commitment, but you generally only lock in your interest rate for a few years at a time. The bank knows that a low rate today does not guarantee a low rate in 2030 or 2035. Historically, interest rates move in cycles. By testing your income against a much higher rate, the bank is ensuring that if the global economy shifts and rates skyrocket in the future, you won't immediately face a financial crisis when it comes time to refix.

2. The legal requirement for responsible lending

New Zealand banks operate under strict government legislation, primarily the Credit Contracts and Consumer Finance Act (CCCFA). Under the responsible lending code, banks are legally obligated to ensure they do not lend you money that will put you into financial hardship. If a bank lent you money based purely on today's low rates without a buffer, and rates subsequently went up, the bank could be heavily penalised by regulators for irresponsible lending.

3. The 'life happens' buffer

The stress test isn't just about interest rates; it acts as an overarching safety buffer for your life. When the bank tests your maximum lending capacity at a higher rate, they are artificially inflating your calculated expenses to see how much "spare cash" you have left over. That spare cash proves you can absorb unexpected life shocks—whether that is a sudden jump in council rates, a massive car repair bill, or having to go on a single income for a few months.

Why your everyday living expenses matter just as much

It is easy to get hung up on the test rate, but the reality is that the interest rate the bank uses is often less important than how they calculate your everyday living expenses.

Under current lending standards, banks have to be incredibly thorough when deciding what it costs you to simply live your life. They apply strict formulas to find your borrowing capacity limits, and the catch is that different banks treat specific lifestyle expenses very differently.

A lower test rate won't help you if a bank's expense calculator aggressively wipes out your spare cash. Here is exactly what they are looking at:

Childcare costs and the double-dip effect

Some banks calculate your childcare expenses as a completely separate, additional cost on top of your baseline household expenses, while others are more pragmatic.

For example, imagine a single parent who actually spends $1,000 per month on basic living expenses, plus $2,000 per month on daycare. Both Bank A and Bank B have an internal rule that a single borrower with one child must spend a minimum of $1,500 per month on basic living expenses—even though this specific borrower is more frugal.

Read more here on how Childcare expenses affect how much you can borrow.

Factoring in your KiwiSaver contributions

If you generously contribute 8% or 10% to your KiwiSaver, nearly all banks will accept that you could lower your contribution back to the 3.5% minimum if things got tight. Some might even allow you to suspend your contributions altogether in their calculator to afford your mortgage, but deciding to pause your retirement savings is not a decision to be taken lightly.

The difference in baseline household expenses

Every bank assumes different families spend different amounts just to keep the lights on. Bank A might assume a couple with one child spends a minimum of $1,200 per month on life expenses (food, clothing, internet, power), while Bank B might deem $1,800 per month to be more appropriate.

Finding the right calculator for your lifestyle

When you walk into a single bank branch, you are entirely at the mercy of their specific, internal stress test and their unique rules for calculating your everyday expenses. If their expense benchmarks are harsh regarding your childcare or KiwiSaver contributions, you will get less money.

To test out your borrowing capacity for yourself, try our Borrowing Power Calculator for a quick, indicative estimate.

Want to know exactly what you can actually borrow? Get in touch with the team at Home Loan Factory today for a clear, easygoing chat.