Methodology

Data sources

All calculators are built on official New Zealand government data. Primary sources include:

• Inland Revenue (IRD): PAYE tax rates and thresholds, KiwiSaver contribution rules, tax credits, student loan repayment thresholds.
• ACC: Earners' levy rates applied to liable income.
• Ministry of Business, Innovation and Employment (MBIE): Minimum wage rates, employment standards.
• Stats NZ: CPI and inflation data used in the inflation and cost-of-living calculators.

Financial year

Unless stated otherwise, all calculators use 2026–27 rates (1 April 2026 – 31 March 2027). The current financial year is shown at the top of each calculator.

Update policy

Tax and financial calculators are updated at the start of each financial year (1 April). If the government announces mid-year changes, calculators are updated as quickly as possible after the change takes effect.

Accuracy testing

Every calculator goes through a three-step verification process before being published:

1. Formulas are implemented directly from the official source tables (e.g., IRD PAYE deduction tables, ACC earner’s levy schedule, MBIE minimum wage order).
2. Results are cross-checked against the official IRD PAYE calculator and relevant government tools using a range of test inputs covering typical, minimum, and maximum values.
3. Edge cases are tested: zero income, incomes at exact bracket boundaries ($14,000, $48,000, $70,000, $180,000), maximum ACC liable earnings ($156,641), and leap-year adjustments for daily/weekly calculators.

Where a calculator produces a result that differs from the official IRD tool by more than $0.01, we investigate and correct the implementation before the calculator goes live.

Key formulas

For transparency, here are the core formulas used in the most popular calculators:

• PAYE income tax: Progressive bracket calculation: 10.5% on first $14,000 + 17.5% on $14,001–$48,000 + 30% on $48,001–$70,000 + 33% on $70,001–$180,000 + 39% above $180,000, plus ACC earner’s levy at $1.75 per $100 of liable earnings up to $156,641.
• GST: Add GST: amount × 1.15. Remove GST: amount ÷ 1.15. Find GST component: amount × 3/23.
• KiwiSaver: Employee contribution (3–10% of gross salary) + employer contribution (3.5% minus ESCT) + government contribution (25c per $1, capped at $260.72/year), compounded annually at the selected fund return rate.
• Mortgage repayments: Standard amortisation formula: M = P[r(1+r)^n] / [(1+r)^n – 1], where P = principal, r = periodic interest rate, n = total number of payments. Supports weekly, fortnightly, and monthly frequencies.

Browser-based calculations

All calculations are performed client-side in your browser using JavaScript. No input data is sent to our servers. This means results are instant and your financial information stays private.

Found an error?

If you believe a calculator is producing incorrect results, please email info@calk.nz with details of the input values and the expected result. We aim to investigate all reports within 2 business days.