This New Zealand calculator lets you test whether you could still afford your mortgage if interest rates rose, the same kind of stress test banks apply when assessing your loan. You enter your loan details and current rate, then a higher test rate, and the tool shows how much your repayments would increase and what that would do to your budget. It is invaluable both for buyers wanting to borrow safely below their limit and for existing homeowners facing a refix at higher rates. The breakdown compares your current repayment with the stressed repayment, shows the monthly and annual difference, and highlights the buffer you would need, helping you avoid borrowing right up to the edge and prepare for rate rises before they arrive.
Repayments are calculated on a table (principal and interest) basis over the remaining term. A test rate a few percentage points above your current rate is a sensible resilience check. Make sure your budget could absorb the extra before borrowing to your limit. Estimate only, not financial advice.
The calculator works out the principal and interest repayment on your loan at both your current rate and a higher test rate, over the term you enter. The difference is what your repayments would rise by if rates climbed to the test level. Seeing this in advance shows whether you have a comfortable buffer or are stretched, which is exactly what a lender checks before approving a loan.
A $600,000 loan over 30 years at 6.5% costs about $3,792 a month. At an 8.5% test rate, the repayment rises to around $4,614, an extra $822 a month or close to $9,900 a year. If your budget could not absorb that, it is a sign to borrow less or build a bigger buffer.
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