How much does a 1% rate rise add to my mortgage?

On a large balance, even 1% adds a meaningful amount each month. The exact figure depends on your balance and remaining term, which this calculator works out by comparing repayments at your current and higher rates.

Why stress test for a rate rise?

Rates move over time, and most mortgages re-fix every year or two. Testing how a rise would affect your budget now helps you avoid being caught short when your fixed term ends or floating rates climb.

What can I do to soften a rate rise?

Pay extra while rates are low to reduce the balance, build a buffer, split your loan across terms, or extend the term (which lowers repayments but adds interest). Knowing the impact early gives you time to act.

Interest Rate Rise Impact Calculator

This calculator shows how a rise in your mortgage interest rate would change your repayments, so you can see the impact before it happens rather than after your fixed rate rolls off. Most New Zealand mortgages are fixed for one or two years, and when the term ends you refix at whatever rate is on offer, which may be higher than your current one. You enter your remaining mortgage balance, current interest rate, the rate rise you want to test (1% or 2% is a good starting point), and how many years remain on the loan. The calculator works out your current table repayment and your new repayment at the higher rate, then shows the extra you would pay each month and each year. It uses the same logic banks apply when they stress test new lending against a higher test rate, giving you a realistic sense of how exposed your budget is to rising rates. Use the results to decide whether to pay down debt faster while rates are lower, build a cash buffer, split your loan across different fixed terms, or simply plan ahead for a bigger repayment. This is an indicative estimate based on standard table loan repayments and does not account for fees, offset accounts or changes to your loan structure.

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Mortgage balance

Current rate

Rate rise to test

Remaining term (years)

extra per month if the rate rises

Current repayment$0

New repayment$0

Extra per year$0

Compares table repayments at your current rate and the higher rate over the remaining term. Banks test new lending against a higher "test rate" for the same reason. Estimate only, not a loan offer.

How it works

The calculator works out the table repayment on your balance at your current rate and at the current rate plus the rise you enter, over the remaining term. The difference is the extra you would pay each month and year if rates climbed that much. It is a simple stress test, the same idea banks use when they check new lending against a higher test rate.

Worked example

On a $550,000 balance over 25 years, a rise from 5.79% to 7.79% lifts the repayment from about $3,475 to $4,164 a month, around $689 more a month, or about $8,270 a year.

Related calculators

Fixed-Rate Rollover Calculator: when a fix ends.
Mortgage Stress Test Calculator: test affordability.
Mortgage Repayment Calculator: repayments.
Borrowing Capacity Calculator: what you can borrow.

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