Mortgage calculator
Calculate your monthly mortgage payment, total interest paid, and full repayment cost.
MSc Finance, Chartered Accountant (ICAEW)
Financial analyst with 12 years experience in mortgage advisory, investment planning and personal finance education.
What if?
Mortgage balance over time
Payment schedule
| Year | Total paid | Principal | Interest | Balance |
|---|---|---|---|---|
| Year 1 | NZ$17,686 | NZ$4,601 | NZ$13,085 | NZ$235,399 |
| Year 2 | NZ$17,686 | NZ$4,860 | NZ$12,826 | NZ$230,539 |
| Year 3 | NZ$17,686 | NZ$5,134 | NZ$12,552 | NZ$225,405 |
| Year 4 | NZ$17,686 | NZ$5,424 | NZ$12,262 | NZ$219,981 |
| Year 5 | NZ$17,686 | NZ$5,730 | NZ$11,956 | NZ$214,252 |
| Year 6 | NZ$17,686 | NZ$6,053 | NZ$11,633 | NZ$208,199 |
| Year 7 | NZ$17,686 | NZ$6,394 | NZ$11,291 | NZ$201,804 |
| Year 8 | NZ$17,686 | NZ$6,755 | NZ$10,931 | NZ$195,049 |
| Year 9 | NZ$17,686 | NZ$7,136 | NZ$10,550 | NZ$187,913 |
| Year 10 | NZ$17,686 | NZ$7,539 | NZ$10,147 | NZ$180,374 |
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About the Mortgage calculator
A mortgage is the single largest financial commitment most people ever make, yet few fully understand what drives their monthly payment. This calculator uses the standard amortisation formula to show you the exact cost of borrowing, month by month, over your chosen term.
By adjusting the home price, deposit, interest rate and term you can instantly see how each variable affects your payment and the total amount you repay. A small change in rate — say 0.5% — can mean tens of thousands of pounds more or less in interest over 25 years.
Use the amortisation schedule below to see exactly how much of each payment goes to principal versus interest. In the early years, the majority of every payment is interest; only near the end of the term does the principal portion dominate. This is called negative amortisation in reverse — understanding it helps you make better decisions about overpayments and remortgaging.
How it works
Monthly Payment = P × [r(1 + r)ⁿ] / [(1 + r)ⁿ − 1] Where: P = Loan amount (home price minus deposit) r = Monthly interest rate (annual rate ÷ 12 ÷ 100) n = Total number of monthly payments (years × 12)
Where
PPrincipal — the loan amount after your deposit is subtractedrMonthly rate — divide your annual rate by 12 and by 100nNumber of payments — mortgage term in years multiplied by 12Worked example
Home price: NZ$300,000 · Deposit: NZ$60,000 → Loan P = NZ$240,000
Annual rate: 5.5% → r = 5.5 ÷ 12 ÷ 100 = 0.004583
Term: 25 years → n = 300 monthly payments
Factor = (1 + 0.004583)³⁰⁰ = 3.846
Monthly payment = NZ$240,000 × (0.004583 × 3.846) / (3.846 − 1)
= NZ$240,000 × 0.01763 / 2.846
= NZ$240,000 × 0.006194
= NZ$1,486.56 / month
Total repaid: NZ$1,486.56 × 300 = NZ$445,968
Total interest: NZ$445,968 − NZ$240,000 = NZ$205,968
Tips to improve your result
- 1.
A 10% deposit gets you on the ladder, but aim for 20% if possible — LTVs below 80% unlock significantly better rates, often saving 0.5–1% per year.
- 2.
Even NZ$100 extra per month on a NZ$240,000 mortgage at 5.5% cuts the term by roughly 2.5 years and saves around NZ$18,000 in interest.
- 3.
When your fixed rate ends, don't let it roll to the lender's standard variable rate (SVR). Remortgage proactively — SVRs are typically 2–3% above the best fixed deals.
- 4.
Compare your mortgage's overall cost (APRC), not just the headline rate. A product with a low rate but high fees may cost more over the full term.
- 5.
If you're self-employed or have a complex income, use a broker. They have access to specialist lenders who may offer you a much better deal than high-street banks.
Reference table
Typical New Zealand LTV tiers and rate impact (2025 guide)
| LTV | Deposit needed (NZ$300k home) | Rate tier | Typical 2-yr fix |
|---|---|---|---|
| 60% | NZ$120,000 | Best rates | ~4.0% |
| 75% | NZ$75,000 | Competitive | ~4.3% |
| 80% | NZ$60,000 | Good rates | ~4.6% |
| 85% | NZ$45,000 | Standard | ~4.9% |
| 90% | NZ$30,000 | Higher | ~5.3% |
| 95% | NZ$15,000 | Highest | ~5.8% |