What the calculator includes—and what it does not.
The model is designed for consistent term comparison, with assumptions made visible so the result can be interpreted sensibly.
Payment calculation
Payments use the standard principal-and-interest amortisation formula. The annual rate is divided into 12 monthly or 26 fortnightly payment periods, and the scheduled payment is calculated across the remaining loan term.
Fixed-term comparison
Both choices are compared over the longer fixed-term period. When the shorter fix expires, the payment is recalculated using one constant average future rate for the remainder of that comparison period.
Break-even rate
The break-even is the non-negative average future rate at which the shorter-fix path and longer fix accrue the same estimated interest. It is a threshold for exploring scenarios, not a forecast of the next bank rate.
Rate data
Advertised rates are supplied by ratesapi.nz from publicly available lender pricing and are checked hourly. MyRefix tracks nine lenders and displays the most recent successfully retrieved dataset. Rates, fees, eligibility and low-equity margins must be confirmed with the lender.
Known differences from lender figures
The estimate does not model exact calendar dates, daily lender accrual, leap years, per-transaction rounding, fees, cashback conditions, offsets, revolving credit, extra repayments or payment changes. These can cause a lender quote or statement to differ.
Using the result
Use MyRefix to understand sensitivity and prepare questions. Consider discussing your complete circumstances with a qualified financial or mortgage adviser before choosing a loan structure.