How the New Zealand take-home pay calculator is verified
Inputs
| Input | Field | Type |
|---|---|---|
| Gross annual salary (NZD) | grossAnnual | 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) |
|---|---|---|
| PAYE | paye | ($t := grossAnnual; $round((($t < 15600 ? $t : 15600) * 0.105) + (($t > 15600 ? (($t < 53500 ? $t : 53500) - 15600) : 0) * 0.175) + (($t > 53500 ? (($t < 78100 ? $t : 78100) - 53500) : 0) * 0.30) + (($t > 78100 ? (($t < 180000 ? $t : 180000) - 78100) : 0) * 0.33) + (($t > 180000 ? ($t - 180000) : 0) * 0.39), 2)) |
| ACC earner levy | acc | $round((grossAnnual < $const.accCeiling ? grossAnnual : $const.accCeiling) * $const.accRate, 2) |
| Net / year | netAnnual | $round(grossAnnual - paye - acc, 2) |
| Net / month | netMonthly | $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.
| Constant | Value |
|---|---|
accRate | 0.0175 |
accCeiling | 156641 |
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 70,000 NZD
given grossAnnual | 70000 |
|---|---|
expect paye | 13220.5 |
expect acc | 1225 |
expect netAnnual | 55554.5 |
Case 2 — S3 200,000 NZD — ACC capped
given grossAnnual | 200000 |
|---|---|
expect paye | 57077.5 |
expect acc | 2741.22 |
Sources
- IRD · checked 2026-08-02
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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