Why this exists

A number you cannot check is not an answer.

Ask what stamp duty you owe and you get a figure. Ask where it came from and most sites go quiet — which would matter less if the rules stood still. They do not: state budgets in May, thresholds on 1 July, New Zealand on 1 April, private health rebates on 1 April again.

Not indexed since 2014–15.

Found on a live surcharge calculator while building this one — a threshold more than a decade out of date, on a page someone is using to make a decision. A second site was publishing last year’s thresholds as current.

Why that happens

Nobody sets out to publish a stale threshold. A calculator is built once, against the rules of that year, and then the rules move and the code does not. There is rarely a date on the page to give it away, and the arithmetic still looks right — which is the problem. A wrong figure with working shown is checkable. A wrong figure alone is indistinguishable from a right one.

So the rules here are not in the code. They are records: a rate, the office that publishes it, the URL, the day the rule took effect, and the day a person opened that page and confirmed it. The calculators read those records, and so does every page that describes them. A rate cannot change in the engine without changing on the sources page in the same commit.

What we do instead

31 of 38rate records verified at the source: Read at 12 offices — the ATO, Services Australia, privatehealth.gov.au and Inland Revenue — not copied from another calculator. Last checked 31 August 2026.
4 yearsof rules held, not just this one: 2023–24 to 2026–27. A past year is worked out on its own rates, which is how an unclaimed exemption or a missed concession can be priced at all.
2figures withheld rather than estimated: One record is incomplete, so the line that depends on it stays blank and says what is missing. A withheld figure is a smaller failure than a confident wrong one.
Nothingstored, sent or tracked: Your figures live in the URL and nowhere else — no account, no email, no analytics. The statement inputs travel in the fragment, so they never reach a server at all.

What this is not

It is not advice. These calculators compute published rules against numbers you type and show the working so you can check both. They do not know your circumstances, and nothing here replaces a registered tax agent, a licensed adviser or a conveyancer. Where a figure cannot be verified it is withheld rather than estimated — including when that leaves an answer incomplete.