How the numbers stay honest

1. Primary sources — and saying so where there are none

Every rate, threshold and concession the law sets comes from the official source — state revenue offices (Queensland Revenue Office, Revenue NSW, the SROs), the ATO, the land registries — and each calculator page lists its sources at the bottom. One figure has no official schedule at all: lenders mortgage insurance. Our LMI bands come from a mortgage broker's published premium table, checked against an insurer's public estimator, and the LMI page names that source and labels every premium an estimate. Where no official source sets a figure — your loan's interest rate, an agent's commission, a conveyancer's quote — the calculator asks for yours rather than inventing one.

2. Dated verification, in the open

A calculator that runs on an official schedule carries a stamp showing the rate year and the date that schedule was last checked against its source, and its Sources section links the source. Calculators whose numbers are yours — a loan's interest rate, a quote you have been given — never carry a rate stamp, because there is no schedule to date: where they carry a stamp at all, it says the arithmetic was checked and the numbers are yours. If a page looks stale to you, tell us — the contact page reaches a human.

3. Engines tested against official worked examples

The calculation engines are covered by an automated test suite of several hundred accuracy tests. The duty and tax engines are pinned to official published figures — worked examples where the revenue office or the ATO publishes them, and the schedule’s own figures where it does not: QRO's example that a $730,000 established first home pays exactly $6,555; Revenue NSW's land tax premium base of $88,036, which our general-rate formula must arrive at exactly at the $6,571,000 premium threshold; Tasmania's published $400,000 land tax example of $1,287.50; the ACT determination's cumulative amounts at every bracket boundary. The loan engines, which have no official examples, are pinned to the closed-form amortisation formulas instead. The suite runs as part of every build: if a change would break a pinned example, the build fails and the site cannot deploy. Most worked examples on our pages are generated by the same engines at build time, so they cannot drift from the calculator the way a typed-in figure can.

4. Probed against the official calculators — to the cent

Where a revenue office publishes its own calculator, ours must match it exactly, and we probe with awkward values chosen to expose rounding rules the documentation doesn't state. Two examples of what that finds. South Australia's land tax legislation charges per "$100 or part of $100" — so $936,150 of site value computes to $1.00, not the 75¢ a straight percentage gives; RevenueSA's calculator confirms it, and ours reproduces it — though no assessment issues below $20, which the engine also applies, so nothing is payable at that value. Western Australia's vehicle duty formula rounds its sliding rate to two decimals and then rounds the duty down to the nearest five cents — a rule stated nowhere on the rates page, discovered by probing RevenueWA's calculator with values like $35,050 (answer: $1,493.10, not $1,493.13). A straight percentage approximates; the schedules don't, and neither do we.

5. Boundary semantics, taken seriously

The expensive errors in tax calculators live at the edges of brackets, where "up to", "not exceeding" and "less than" all mean different things. Our data files encode each state's actual boundary semantics: Victoria's duty bands that switch to a flat percentage of the whole price above $960,000 (so exactly $960,000 stays marginal — the SRO's ">" matters); WA's land tax step that is nil at exactly $300,000 and $300 flat at $300,001; Queensland's first home concession bands that align to the QRO's table rather than a smooth taper. Every one of these edges has a dedicated test sitting exactly on the boundary.

6. The 1 July ritual — and the mid-year watch

Australian rates move on a rhythm: state budgets in May–June, new thresholds and schemes on 1 July, indexation through the year. Every data file is re-verified each July, and again whenever a state announces a change. Some changes don't wait for the new financial year — the ACT's vehicle duty rates rise on 1 February 2027 under a determination already made — so pages carrying a scheduled change say so, with the date. Others are easy to miss even on 1 July: from 1 July 2026 the ACT's Home Buyer Concession has no value limit, so an eligible buyer (no property owned in the past five years, living in the home for a year) pays no duty at any price. Where federal law has already changed future rules (the 2027 capital gains and negative gearing reforms), the affected calculators explain both regimes now rather than springing the change later.

7. Estimates labelled as estimates

Some figures are exact schedules (stamp duty); others are inherently indicative (LMI premiums vary by lender and insurer). Where a number is an estimate, the page says so plainly and explains the uncertainty rather than hiding it — and where eligibility conditions decide which schedule applies to you (first-home tests, residence requirements, foreign-person definitions), the page states the conditions instead of silently assuming them.

8. Independence

No lender, broker, insurer or agent pays Tallyroo to appear anywhere on this site, and no calculator result is shaped by a commercial relationship. When advertising runs on these pages it is clearly marked as advertising, and it never changes a number. We built the calculators we wished existed when doing our own sums — the revenue office's answer, without the lead-gen form in front of it.

The sources matter, and so does who reads them. Tallyroo is run by Rakesh Choudhary, and it publishes arithmetic rather than advice — which is precisely why every page shows its working and cites the schedule instead of telling you what to do.

Corrections

Found an error? We want it. Email us via the contact page — verified corrections are fixed on the affected page and written up in the corrections log, which says what the site said before and how the error was found. It was not empty on the day it was published. What goes in the log, and the rest of the rules every page is held to, are set out in our editorial standards. Tallyroo provides general information only, not financial, legal or tax advice; always confirm significant decisions with the official source or a licensed professional.