How the Australia sole trader calculator is verified

Inputs

Input	Field	Type
Annual profit after expenses (AUD)	`annualProfit`	number

The formula

Each derived value below is computed by the Valem engine from the expression shown, in this order. Nothing else runs — there is no hidden code path.

Derived value	Field	Formula (JSONata)
Income tax	`incomeTax`	`($p := annualProfit; $round($const.rate2 * $max([0, $min([$p, $const.band2]) - $const.freeThreshold]) + $const.rate3 * $max([0, $min([$p, $const.band3]) - $const.band2]) + $const.rate4 * $max([0, $min([$p, $const.band4]) - $const.band3]) + $const.rate5 * $max([0, $p - $const.band4]), 2))`
Medicare levy (2%)	`medicare`	`$round(annualProfit * $const.medicareLevy, 2)`
Net income / year	`netIncome`	`$round($max([0, annualProfit - incomeTax - medicare]), 2)`

Rates and thresholds

The expressions above read these as $const. They are the figures the annual refresh replaces, so they live as data rather than being written into the formulas — which is what makes a year-on-year change a one-line diff instead of an edit to arithmetic.

Constant	Value
`freeThreshold`	18200
`band2`	45000
`band3`	135000
`band4`	190000
`rate2`	0.16
`rate3`	0.3
`rate4`	0.37
`rate5`	0.45
`medicareLevy`	0.02

Test vectors (3)

Every case is executed against this model on each build, by the Java engine and independently by a JavaScript one. A mismatch of a single cent fails the build, so the page cannot ship advertising a figure the model no longer produces.

Case 1 — 90,000 AUD profit — a typical full-time sole trader

given `annualProfit`	90000
expect `incomeTax`	17788
expect `medicare`	1800
expect `netIncome`	70412

Case 2 — 30,000 AUD profit — part-time, second band only

given `annualProfit`	30000
expect `incomeTax`	1888
expect `medicare`	600
expect `netIncome`	27512

Case 3 — 200,000 AUD profit — into the top band

given `annualProfit`	200000
expect `incomeTax`	56138
expect `medicare`	4000
expect `netIncome`	139862

Sources

ATO — Individual income tax rates · checked 2026-08-22
Sole trader tax in Australia 2025–26: rates, thresholds and the Medicare levy · checked 2026-08-22

Check it yourself — and reuse it

The whole model as JSON — inputs, outputs, formulas, vectors and sources in one re-runnable document.

This model is published under CC BY 4.0: use it, adapt it, build on it, with attribution. The licence covers the model — the expression of each rule and the arrangement of the catalog. The rates and thresholds are law, and nobody licenses those; the sources above are where they come from.

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