How the South Africa sole proprietor calculator is verified

Inputs

Input	Field	Type
Annual taxable profit (ZAR)	`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)
Tax before rebate	`taxBeforeRebate`	`($p := annualProfit; $round($const.r1 * $min([$p, $const.b1]) + $const.r2 * $max([0, $min([$p, $const.b2]) - $const.b1]) + $const.r3 * $max([0, $min([$p, $const.b3]) - $const.b2]) + $const.r4 * $max([0, $min([$p, $const.b4]) - $const.b3]) + $const.r5 * $max([0, $min([$p, $const.b5]) - $const.b4]) + $const.r6 * $max([0, $min([$p, $const.b6]) - $const.b5]) + $const.r7 * $max([0, $p - $const.b6]), 2))`
Income tax after primary rebate	`incomeTax`	`$round($max([0, taxBeforeRebate - $const.primaryRebate]), 2)`
Net income / year	`netIncome`	`$round($max([0, annualProfit - incomeTax]), 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
`primaryRebate`	17820
`b1`	245100
`b2`	383100
`b3`	530200
`b4`	695800
`b5`	887000
`b6`	1878600
`r1`	0.18
`r2`	0.26
`r3`	0.31
`r4`	0.36
`r5`	0.39
`r6`	0.41
`r7`	0.45

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 — 600,000 ZAR taxable profit — a typical full-time consultant

given `annualProfit`	600000
expect `taxBeforeRebate`	150727
expect `incomeTax`	132907
expect `netIncome`	467093

Case 2 — 150,000 ZAR — the rebate covers most of the tax

given `annualProfit`	150000
expect `taxBeforeRebate`	27000
expect `incomeTax`	9180
expect `netIncome`	140820

Case 3 — 2,000,000 ZAR — into the top bracket

given `annualProfit`	2000000
expect `taxBeforeRebate`	720969
expect `incomeTax`	703149
expect `netIncome`	1296851

Sources

SARS — Provisional tax · checked 2026-08-22
SARS tax tables 2026/2027 — individual brackets and rebates · 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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