About this calculator
New Zealand is the simplest big mortgage market in the English-speaking world at purchase time: there is no stamp duty, no transfer tax and no first-home buyer duty scheme to model, because none exists. (KiwiSaver first-home withdrawals and the First Home Grant help with the deposit itself, not with a purchase tax.) What does deserve a proper calculator is the way Kiwis actually run their loans: large offset and revolving-credit facilities that keep everyday money working against the mortgage balance.
That is what this calculator models. Your repayment is calculated on the full loan, but interest is charged on the balance minus your average offset/revolving balance — so the loan clears years earlier without the repayment changing. If your deposit is under 20%, banks add a low-equity cost (a one-off premium or a margin); the estimate here capitalises a premium in the Australian LMI style, which is the right order of magnitude for NZ low-equity fees — check your bank's exact charge, as they differ.
How to use it
- Enter the property price and your deposit — the difference, plus any LMI, is the loan amount.
- Add the interest rate and loan term (30 years is the Australian standard).
- If you will keep savings in an offset account, enter the average balance — you will see the interest it saves and how much sooner the loan ends.
- Tick "first home buyer" if it applies: the stamp duty below then uses your state's first-home concessions.
- Read the monthly repayment, the stamp duty and the real payoff time with your offset.
The formula
M is the monthly repayment, P the loan amount, r the monthly rate and n the number of payments. An offset account does not change the repayment; it reduces the balance on which interest is charged, so more of each repayment becomes principal and the loan ends sooner. Stamp duty is charged by the state on the purchase price using that state's banded table.
Worked example
An NZ$800,000 home with a $160,000 deposit (20%) leaves a $640,000 mortgage. At 6.00% over 30 years the repayment is $3,837 a month and the stamp duty is $0 — there is none to pay. Keep an average of $50,000 sitting in an offset or revolving-credit account and the same loan is repaid in 25 years 7 months, saving about $204,666 in interest over its life: the single most valuable feature in NZ mortgage banking, and the reason so many Kiwi loans are structured around it.
Frequently asked questions
Does New Zealand have stamp duty on property?
No. New Zealand abolished stamp duty on property transfers and does not charge any purchase tax on homes — no duty, no transfer tax, no land tax for owner-occupiers. Your purchase costs are legal fees (about $2,000–$3,500), a LIM report, a building inspection and possibly a registered valuation: typically well under 1% of the price, against 3–5% of duty in Australia.
How do offset and revolving credit facilities save interest in NZ?
Interest is calculated daily on your balance minus the money parked in linked offset accounts, or on the net balance of a revolving-credit facility you pay your salary into. The repayment does not change, so every dollar of interest saved becomes principal. $50,000 held steadily against a $640,000 loan at 6% saves roughly $204,666 across the life of the loan in this model and shortens it by about 4 years 5 months — but the balance must actually stay there; money that flows out stops saving interest the day it leaves.
What does a deposit under 20% cost in NZ?
Banks must limit low-equity lending under Reserve Bank LVR rules, and they charge for it: either a low-equity premium (a one-off fee, often 0.25%–1%+ of the loan, sometimes capitalised) or a low-equity margin added to your rate until the equity builds. The calculator uses a premium curve similar to Australian LMI as an estimate — at 90% LVR about 3% of the loan — but NZ charges vary by bank and are sometimes a rate margin instead, so treat the figure as a budgeting guide.
Should I split my NZ mortgage into fixed and floating parts?
Many Kiwis do: a floating (or offset/revolving) portion for flexibility and lump-sum repayments, and fixed portions for certainty. This calculator prices a single loan at one rate across the term, which is the right way to compare total interest between structures. Model the floating part by entering the rate you expect to average and an offset balance you will realistically keep — small honesty about the balance matters more than the split itself.
What formula does this mortgage calculator — new zealand calculator use?
M = P × r(1 + r)^n ÷ ((1 + r)^n − 1), interest charged on (balance − offset) M is the monthly repayment, P the loan amount, r the monthly rate and n the number of payments. An offset account does not change the repayment; it reduces the balance on which interest is charged, so more of each repayment becomes principal and the loan ends sooner. Stamp duty is charged by the state on the purchase price using that state's banded table. The worked example on this page applies the formula step by step with real numbers, so you can verify the result by hand.