How we work out your numbers

We only use rates from our maintained rate table, which is refreshed regularly and stamped with the date it was last updated. Mortgage-review comparisons use the lowest eligible rate for the fixed term selected. First-home results use offers marked as available to first-home buyers, while borrowing-power results use the applicable rate held in the table without adding a margin of our own.

If we cannot find an applicable rate, the result says so rather than silently substituting an unrelated rate. A displayed rate is an input to an indicative calculation, not an offer.

When you tell us your balance, your rate, your repayment and how long you have left, we rebuild your loan one month at a time. Each month we work out the interest on what you still owe, take that off your repayment, and reduce the balance by what is left. We keep going until the loan reaches zero, or until 30 years have passed.

Doing it month by month rather than with a single formula is what lets us show a payoff date, the total interest, and how a change today plays out over the years.

Alongside your loan as it stands, we run the same month-by-month calculation on two alternatives: keeping your repayment exactly where it is, and dropping it to the lowest required amount. Where a lender contribution applies, we treat it as reducing your balance on day one, after allowing an assumed $1,500 for legal costs.

Lifetime figures can look surprisingly large. That is because a small rate difference is held for the whole remaining term, and because anything extra you keep paying comes straight off the balance, so it saves interest every month after that.

Borrowing estimates start with your income, subtract tax, your other debt repayments and your living costs, and test what is left against a repayment over a 30-year term while keeping a monthly buffer spare.

Customer-entered expenses, household spending statistics and lender-style minimum allowances are different things. If you enter your living expenses, we preserve and use that amount exactly. We do not increase it to a benchmark. Only when you leave expenses blank do we use our configured household estimate, which is maintained with its source and review date. Vehicle running costs follow the same entered-first rule.

For buying, we compare your savings, KiwiSaver and any gift against a 20%, 10% and 5% deposit on the price you have in mind, and show the gap for each. We then note which routes could be open to you, including low-deposit lending and the Kāinga Ora First Home Loan, using published scheme settings for income and house price caps.

The rent comparison lines up your rent against the loan repayment only. Council rates, insurance, maintenance and any body corporate levies are on top, and we say so on the report.

We do not include break fees on a fixed rate, lender application or valuation fees, or your own moving costs. Where your loan would sit above 80% of the property value, we flag that a low-equity margin usually applies but we do not price it in. We do not model rates or your circumstances changing over time, and we do not use rates that are only available through an adviser assessment.

These calculators are here to give you a clear, honest starting point. They are indicative only, they use the details you give us without verifying them, and lender criteria can change at any time. Before acting on anything you see here, speak with a qualified mortgage adviser.