Mortgage Offset Calculator

An offset account is a regular transaction or savings account linked to your mortgage. The balance in the offset is subtracted from the loan balance for interest calculation — so $20k in offset + $400k mortgage = bank charges interest on $380k. Available from Kiwibank (Offset), Westpac (Choices Floating with Offset). Offsets work on floating-rate loans only. Source: Kiwibank, Westpac.

It depends. Offsets are floating-rate (~7.85% in mid-2026) vs fixed (~6.25%). The offset saves interest tax-free; a fixed rate is cheaper but you can't avoid interest on the full balance. Rule of thumb: if your offset balance is at least ~30% of your loan, the floating + offset can beat a fixed rate. Source: MoneyHub.

Yes, with restrictions. Kiwibank Offset Home Loan allows up to 8 linked accounts, including ones owned by direct family members (parents, adult children, spouse, siblings). All linked account-holders must agree in writing. Westpac Choices Floating with Offset is single-account only. The benefit: parents and grandparents can effectively 'donate' their savings interest to your mortgage without giving you the cash. The risk: if a linked holder withdraws funds, your effective offset drops and your interest charges rise. Family offset arrangements should ideally be documented in a side agreement. Source: Kiwibank product disclosure statement.

The offset balance earns 0% interest — but in exchange, the offset amount reduces what you pay interest on for the mortgage. This is mathematically equivalent to earning the mortgage rate (e.g. 7.85% floating) on your savings, tax-free. Compare: a regular NZ savings account at 4.5% taxed at 33% RWT gives you 3.02% net. An offset against a 7.85% mortgage gives an effective tax-free benefit of 7.85% — 2.6× better. The catch: offsets only work on floating-rate loans, which are about 1.5% higher than 2-year fixed (~6.25%). Run the numbers carefully with the calculator above. Source: MoneyHub offset guide.