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Ozisuma

About

What this site is

Ozisuma (ozisuma.com) is an independent project that builds Australian-specific calculators for everyday financial questions: stamp duty across the eight states and territories, HECS-HELP repayments, superannuation projections, working holiday tax, crypto tax, take-home pay, and the running cost of property and life in AUD.

The focus is the detail that the big bank calculators and the official ATO/Revenue NSW tools usually skip — first-home concessions, foreign-purchaser surcharges, off-the-plan rules, state-by-state comparisons — with the source rate card linked on every page.

Every calculation runs in the browser. Your inputs are never sent to a server.

Why this site exists

Australia has eight different state and territory revenue offices, a unique HECS-HELP system that does not exist anywhere else, a superannuation regime with its own caps and contribution rules, and a property market where stamp duty alone can vary by tens of thousands of dollars from state to state. The calculator landscape that has grown up around all of this is dominated by the big banks, two property portals (Domain, realestate.com.au) and a handful of comparison sites — most of which build a thin tool to capture mortgage broker leads rather than to answer the user's real question.

The official tools at the ATO and the state revenue offices are accurate but designed for tax practitioners. They rarely walk through the assumptions, never compare across states, and almost never explain the "why" behind a number. The gap between an authoritative-but-opaque ATO calculator and a slick-but-shallow bank widget is exactly the gap this site sets out to fill: Australian-context calculators that show the working, link the legislation, and run on the same FY2025-26 thresholds the ATO uses for assessment.

Each calculator on the site is built from a single source of truth: ato.gov.au for federal tax, the eight state revenue offices for stamp duty and land tax, fairwork.gov.au for awards and minimum-wage matters, treasury.gov.au and rba.gov.au for indexation rates and policy proposals. We do not derive numbers from third-party blogs, mortgage broker websites or unofficial spreadsheets. Where a figure is contested or proposed (for example, the marginal HECS-HELP system pending legislation, or the Division 296 high-balance super tax) the calculator clearly flags the legislated baseline and lets you toggle the proposed alternative.

How figures are verified

The verification process is deliberately boring: every dollar threshold, percentage rate and cap is traced back to a primary source on a .gov.au domain, and the URL is recorded in the calculator's source list at the bottom of the page. When the ATO publishes its annual update (typically May to June, for the financial year that begins on 1 July), the rates are reviewed line-by-line against the new schedule before the "Updated" date on the calculator page is bumped. Quarterly checks are done for the figures that move out-of-cycle — the cash rate (RBA), the Superannuation Guarantee rate (legislated steps), and the Medicare Levy thresholds (CPI-linked).

The full editorial standard — the source whitelist, the update cadence, the YMYL stance and the correction policy — is published on the Methodology page.

Each calculation function is implemented as a pure function with unit tests. The tests include the worked examples published in the official sources — the Revenue NSW worked examples for stamp duty, the ATO's example tables for HECS-HELP, the SRO Victoria worked examples for land tax — so that a calculator that disagrees with the official worked example fails its tests and does not ship. As of the launch of this Guides section the test suite covers 600+ unit tests across 60+ calculators.

Update cadence

Australia's tax and welfare calendar drives the update cadence. The biggest single review window is around the Federal Budget (the second Tuesday in May), when income tax bands, super caps, and Medicare Levy thresholds are typically refreshed. The second cluster is the start of the financial year (1 July), when the new figures take effect and payroll software is updated. State Budgets in May and June often reset stamp duty thresholds, land tax brackets and payroll tax rates; we follow each state's revenue office release.

Outside those windows, a monthly automated fact-check sweep re-validates the cited figures against the official sources, flags any drift, and opens a pull request to update the affected pages. The "Updated" date at the top of every calculator and guide page tells you the version you are looking at.

The editorial desk

Writing and review across the site are attributed to the Ozisuma Editorial Desk — a single collective editorial identity we use instead of an individual byline, so that every calculator and guide goes through the same editing and fact-checking process. An independent editorial team that turns figures published by the ATO, state revenue offices and Services Australia into clear, source-cited calculators for Australian residents, and re-checks them as rates and thresholds change.

The work is organised into desks by topic, each tracking its own official sources:

Every calculator page carries the line "Written and reviewed by Ozisuma Editorial Desk" alongside its Updated and Last reviewed dates. To report an error or request a correction, email [email protected].

Who runs it

Editorial policy

How the site is funded

The site is funded by Google AdSense and by affiliate programs relevant to the calculator on the page (mortgage brokers, conveyancers, comparison sites, accounting software). Disclosure detail is in the Privacy policy.

Contact

To suggest a new calculator, report a wrong rate or a broken formula, please use the contact page.