How the South Africa salary after tax calculator is verified

Inputs

InputFieldType
Gross annual salary (ZAR)grossAnnualnumber

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 valueFieldFormula (JSONata)
Paye GrosspayeGross($t := grossAnnual; $round((($t < 245100 ? $t : 245100) * 0.18) + (($t > 245100 ? (($t < 383100 ? $t : 383100) - 245100) : 0) * 0.26) + (($t > 383100 ? (($t < 530200 ? $t : 530200) - 383100) : 0) * 0.31) + (($t > 530200 ? (($t < 695800 ? $t : 695800) - 530200) : 0) * 0.36) + (($t > 695800 ? (($t < 887000 ? $t : 887000) - 695800) : 0) * 0.39) + (($t > 887000 ? (($t < 1878600 ? $t : 1878600) - 887000) : 0) * 0.41) + (($t > 1878600 ? ($t - 1878600) : 0) * 0.45), 2))
PAYE (after rebate)paye($p := payeGross - $const.primaryRebate; $round($p > 0 ? $p : 0, 2))
UIFuif$round((grossAnnual < $const.uifCeiling ? grossAnnual : $const.uifCeiling) * $const.uifRate, 2)
Net / yearnetAnnual$round(grossAnnual - paye - uif, 2)
Net / monthnetMonthly$round(netAnnual / 12, 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.

ConstantValue
primaryRebate17820
uifRate0.01
uifCeiling212544

Test vectors (2)

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 — S1 360,000 ZAR single

given grossAnnual360000
expect paye56172
expect uif2125.44
expect netAnnual301702.56

Case 2 — S3 900,000 ZAR

given grossAnnual900000
expect paye247293
expect netAnnual650581.56

Sources

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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