Methodology

Every calculator on Ozisuma is built from a single, traceable chain: a primary source on a .gov.au domain, a pure function that implements the published formula, and a unit-test suite that includes the official worked example. This page explains how that chain works, where the numbers come from, and how often they are reviewed.

How we verify numbers

Every threshold, percentage rate and cap is sourced from a primary document on a .gov.au domain. The url is recorded in the calculator's sources block so a reader can follow the chain themselves.

The formula is then implemented as a pure function in TypeScript: deterministic, with no side effects. The Vitest suite covers 601+ test cases across 60+ calculators — every threshold-crossing edge case and every published worked example. Calculators do not ship until the suite passes.

For Your-Money-Your-Life topics, the worked examples in the test suite are sourced directly from the agency: Revenue NSW for stamp duty, the ATO for HECS-HELP and tax bands, the Fair Work Ombudsman for awards. A calculator that disagrees with the official worked example fails CI and does not ship.

Source whitelist (.gov.au only)

Numbers come from the following primary sources only. We do not derive figures from comparison websites, bank calculators, broker sites, blogs, AI summaries or unofficial spreadsheets.

• ATO (ato.gov.au) — federal income tax, HECS-HELP, super caps, GST, FBT, CGT, PAYG.
• Revenue NSW (revenue.nsw.gov.au) — NSW transfer duty, land tax, payroll tax, surcharge purchaser duty.
• State Revenue Office Victoria (sro.vic.gov.au) — Victorian stamp duty, land tax, vacant residential land tax, windfall gains tax.
• Queensland Revenue Office (qro.qld.gov.au) — QLD transfer duty, land tax, payroll tax.
• RevenueSA, Department of Treasury and Finance WA, SRO Tasmania, Territory Revenue Office NT, ACT Revenue Office — equivalent state and territory revenue offices.
• Fair Work Ombudsman (fairwork.gov.au) — modern awards, minimum wages, leave entitlements.
• Services Australia (servicesaustralia.gov.au) — Centrelink payments, Medicare, Family Tax Benefit, Commonwealth Rent Assistance.
• ABS (abs.gov.au) — Census, household income, CPI, Wage Price Index.
• RBA (rba.gov.au) — cash rate, monetary policy statements.
• ASIC's MoneySmart (moneysmart.gov.au) — independent consumer-facing guidance.
• Treasury (treasury.gov.au) — Budget papers, intergenerational projections, costings.

Sources we reject: Australian banks (CBA, Westpac, NAB, ANZ), property portals (Domain, realestate.com.au), comparison sites (Canstar, Finder), AI summaries, and personal finance blogs.

Update cadence

Australia's tax and welfare calendar drives a predictable annual review cycle:

• Federal Budget night (the second Tuesday in May) — income tax bands, super caps, Medicare Levy thresholds, family payment thresholds. We do a line-by-line review against the new schedule in the week following the Budget and bump the "Updated" date on every affected calculator.
• 1 July (start of the financial year) — most rate changes take effect. Payroll software updates the PAYG schedules, the Superannuation Guarantee rate moves if scheduled, the HECS-HELP repayment thresholds reset, and the state stamp duty bracket boundaries reindex.
• State Budgets (typically May–June, varies by jurisdiction) — stamp duty thresholds, land tax brackets, payroll tax thresholds, foreign purchaser surcharges. Each calculator pinned to a state revenue office is reviewed against the state Budget as it lands.
• Fair Work Annual Wage Review (decision in June, effective from the first full pay period in July) — minimum wage, modern awards. Affected leave-loading, redundancy and award calculators are reviewed.
• Monthly automated fact-check — a scheduled job re-validates the cited figures against the official source on the first of each month, flags any drift, and opens a pull request to update the affected pages. The "Updated" date and the "Last reviewed" date at the top of every calculator and guide page tell you the version you are looking at.

Your-Money-Your-Life stance

Calculators on this site are not personal advice. They are general estimates based on the legislated rates for a financial year. They do not consider your individual circumstances, residency, contract terms or trust structure.

For tax, super, mortgage and Centrelink decisions, speak to a registered tax agent, licensed financial adviser or mortgage broker before acting. Each calculator includes a YMYL-specific disclaimer at the bottom. We use estimate language ("the typical bill is around $X") rather than prescriptive ("you will pay $X").

Correction policy

If you find an error — a wrong threshold, a stale rate, or a formula that disagrees with the official worked example — please use the contact page. We commit to fixing material errors within 48 hours of discovery, with the "Updated" and "Last reviewed" dates incremented and the test suite updated so the same drift is caught in CI.

For broader editorial context see the About page. To suggest a new calculator, the contact page is the fastest route.