KiwiTools guide
How KiwiTools calculations work
We keep formulas, assumptions, data sources and limitations visible so you can understand what drives each estimate.
PAYE and income calculations
For the 2027 tax year, income is annualised and each portion is taxed using the applicable progressive bracket. ACC is calculated separately up to maximum liable earnings. Selected KiwiSaver and student-loan deductions are then applied. Pay converters and average-daily-pay tools use the work periods and earnings entered rather than inferring an employment entitlement.
Electricity and solar calculations
Appliance cost uses watts divided by 1,000, multiplied by usage time, duty cycle and the entered price per kWh. Bill estimates separate variable usage, daily charges, other charges, discounts and GST. Solar payback models entered installation cost, generation, self-use, export and degradation assumptions; it is not a forecast or quote.
Mortgage and property calculations
Mortgage results use the standard amortising-loan formula with the entered principal, rate, frequency and term. Property tools use entered deposits, buying costs, council rates, rent, vacancy and expenses. They do not determine lending approval, KiwiSaver eligibility, a council assessment or a property-specific market value.
Transport and comparison calculations
Fuel cost uses distance, fuel economy and pump price. RUC uses the selected rate and distance units. EV, mobile-plan and flight comparisons place entered alternatives on a common annual, trip or ownership-period basis. Prices, fees, resale values and inclusions remain assumptions unless the page identifies an official rule.
Everyday checkers and planners
The annual-leave planner combines the selected work pattern with maintained public-holiday and regional-anniversary dates. The school-zone checker matches an address location against mapped enrolment-zone data and flags boundary uncertainty. School-zone results must be confirmed with the school or Ministry of Education.
Browser calculations and external services
Calculator inputs and results are normally processed in the browser. Features that require external data, such as address lookup and mapped school zones, can call a configured service. The contact form sends only the details the user chooses to submit to the KiwiTools contact service.
Rounding, presets and limitations
Calculations retain unrounded values where practical and format results for display in NZD or the relevant unit. Presets are illustrative starting points, not current offers, market forecasts or recommendations. Real outcomes can differ because rules, eligibility, rates, fees, dates, provider data and personal circumstances change.