Your repayment if rates rise to the test level.
Repayment at the test rate
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Current repayment
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Extra per month
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Your breakdown
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The day your fixed rate rolls over
Most New Zealand mortgages are fixed for one to three years, not for the whole term. That is the quiet risk in our market. When your fixed period ends you refix at whatever rate is going, and if rates have climbed since you last locked in, your repayment jumps overnight with no warning and no transition. A stress test answers the question your bank already asked itself before lending to you: could you still afford the loan if the rate were a lot higher? This tool recalculates your repayment at a test rate so you can see the new number before the market hands it to you.
Banks run exactly this check during the approval process, using a servicing or test rate that sits well above current pricing, commonly around 8 to 9 percent, to make sure borrowers have headroom. Running your own version is simply prudent. It turns an abstract worry into a dollar figure you can plan around.
A $600,000 loan tested from 6.5 to 9 percent
Take a $600,000 mortgage over 30 years. At today’s 6.5 percent the repayment is $3,792 a month. Stress it at a 9 percent test rate, holding the term at 30 years, and the repayment climbs to $4,828. That is an extra $1,035 a month, a 27 percent jump, that your budget would need to absorb if your fixed term rolled onto that higher rate.
An extra $1,035 a month is $12,420 a year of after-tax income you would need to find. For most households that is the difference between comfortable and stretched, which is precisely the point of testing it in advance.
Building the headroom before you need it
If the test repayment looks tight, you have options, and the best time to act on them is while you are still on the lower rate. The most powerful move is to voluntarily pay the higher amount now. Set your repayment at the $4,828 test figure today, while you are only obliged to pay $3,792, and two good things happen. You prove to yourself that the budget copes, and the extra $1,035 goes straight onto the principal, so you arrive at your refix with a smaller loan and a built-in cushion. It is a stress test and a head start at once.
The other lever is how you spread your fixed terms. Splitting the loan so that only a portion refixes at any one time means a rate spike only hits part of your debt at a time, softening the blow. A common mistake is fixing the entire mortgage for the same short term, which maximises your exposure to whatever rate happens to be on offer on a single day. Worth noting too: there is no general capital gains tax in New Zealand, so for an owner-occupier the home itself is not a tax problem, but the bright-line test can tax the gain if you sell certain residential property within two years of buying it, which matters if higher repayments ever tempt you to sell early.
What test rate should I use for my own check?
Pick a rate a few percentage points above your current one, and ideally above the highest rate you have seen in recent years. Banks have used figures around 8 to 9 percent, so testing at 9 percent is a sensible stress level even when current rates are lower. If you can afford the repayment at that rate, you have genuine resilience against a refix shock.
Why hold the term constant in the stress test?
Holding the term fixed isolates the pure effect of the rate change on your repayment, which is what you feel in your budget. In reality, when you refix, the remaining term will have shortened, so your actual future repayment depends on both the new rate and the years left. This tool deliberately compares like for like over the same term so the increase you see is driven by the rate alone.