Mortgage Repayment Calculator NZ

See your repayments, total interest, and how extra payments — or an interest-only period — affect the total cost of your mortgage.

About this calculator

Understanding your mortgage repayments is the first step to taking control of your biggest debt. This calculator uses the standard amortisation formula to show your exact repayment at any frequency, plus how much interest you'll pay over the life of your loan — and how much a small extra payment could save you.

How are NZ mortgage repayments calculated?

NZ mortgages use the standard amortisation formula: your repayment is calculated so that equal payments over the full term will exactly pay off both the principal and the interest. Each payment covers that period's interest first, with the remainder reducing the principal. Early in the loan, most of each payment goes to interest. As the balance falls, the interest portion shrinks and more goes to principal.

Most NZ mortgages are repaid fortnightly, which means you make 26 repayments a year — the equivalent of 13 monthly payments instead of 12. That extra payment each year quietly accelerates your mortgage payoff, shaving years off a typical 25-30 year term. Any debt calculator you use should account for fortnightly — not monthly — repayments.

Weekly vs fortnightly vs monthly — which is best?

Fortnightly and weekly payments result in more total payments per year than the monthly equivalent, reducing your balance faster and therefore accruing less interest each period. Fortnightly is the NZ standard and results in 26 payments per year — equivalent to 13 monthly payments. Weekly results in 52 payments — equivalent to 13 monthly payments spread more frequently. Both save more interest than monthly, because your balance is reduced faster and interest has less time to accumulate.

In practice, fortnightly aligns with most New Zealanders' pay cycles, making it easier to budget and less likely that you'll miss a payment. Weekly can squeeze out a small additional saving, but the difference over fortnightly is modest compared to the fortnightly vs monthly gap.

How much does an extra $50 per fortnight save?

On a $500,000 mortgage at 5.5% over 25 years, the standard fortnightly repayment is approximately $1,490. Adding just $50 fortnightly — bringing it to $1,540 — saves around $25,000–$30,000 in interest and cuts roughly 2 years off the term. The earlier you start paying extra, the greater the compounding effect, because every dollar of principal you reduce stops accruing interest for the remaining life of the loan.

Even small extra amounts make a significant difference due to compound interest. Use the calculator above to see exactly how much your specific extra payment would save.

What is a good mortgage repayment in NZ?

A good rule of thumb is that your mortgage repayment should remain manageable if interest rates rise 2–3% above your current rate. NZ banks stress-test affordability at rates significantly above the current fixed rate — typically at a floor of 7–9% depending on the lender and current market conditions.

It's worth using this calculator at your current rate and then again at your current rate plus 2% to see what your repayments would look like if rates move. If the higher-rate repayment would stretch your budget significantly, it may be worth building in some buffer before your next refix.

Interest-only mortgages: what do they cost?

An interest-only (IO) period means you pay only the interest on your mortgage for a set period — typically 1–5 years. Your balance stays exactly the same throughout, and when the IO period ends, you switch to principal and interest repayments for the remaining term. Because you have less time to repay the same balance, your P+I repayments will be higher than if you'd been on P+I from the start.

On a $750,000 mortgage at 5.5% over 25 years, a 2-year IO period costs approximately $24,000 in extra interest compared to standard P+I. A 5-year IO period costs approximately $63,000 more. Use the interest-only toggle in the calculator above to model your specific situation. For a deeper look, read our guide on interest-only mortgages in NZ.

Frequently asked questions

How do I calculate my mortgage repayment in NZ?

Use the standard amortisation formula: repayment = loan × (monthly rate × (1 + monthly rate)^term) ÷ ((1 + monthly rate)^term - 1). Most NZ mortgages use fortnightly repayments — the fortnightly equivalent is the monthly repayment × 12 ÷ 26. This calculator handles all frequency conversions automatically.

What is the average mortgage repayment in NZ?

With median NZ house prices and current fixed rates ranging from around 4.59% for short terms to 6.39% for longer terms (as of May 2026), a typical first-home buyer with a 20% deposit on a $700,000 mortgage might expect fortnightly repayments of around $1,900–$2,300 on a 25–30 year term. Use this calculator with your actual numbers for a precise figure.

Does paying fortnightly instead of monthly save money?

Yes — fortnightly payments result in 26 payments per year, equivalent to 13 monthly payments instead of 12. That extra payment each year can shave years off a typical 25-year mortgage and save tens of thousands in interest over the life of the loan.

How much extra should I pay on my mortgage?

Even small extra amounts make a significant difference due to compound interest. An extra $50–$100 fortnightly on a $500,000 mortgage can save tens of thousands in interest and cut years off your term. Use the 'what if I paid extra' field above to calculate your specific saving.

What happens at the end of an interest-only mortgage period?

At the end of the interest-only period, your repayments switch to principal and interest (P+I) for the remaining term. Because you haven't reduced your principal during the IO period, your P+I repayments will be higher than if you'd been on P+I from the start. For example, on a 25-year term with a 2-year IO period, you repay the full balance over the remaining 23 years — which means higher repayments than a standard 25-year P+I mortgage.

Is an interest-only mortgage a good idea in NZ?

Interest-only periods can make sense for property investors managing cash flow, borrowers during a short-term financial squeeze, or buyers of new builds with high construction costs. They are generally not recommended for owner-occupiers as a long-term strategy, because they delay principal repayment and cost more in total interest. Since 2021, the RBNZ has restricted interest-only lending for owner-occupiers, so approval depends on your lender and circumstances.