How the Netherlands netto loon calculator is verified
Inputs
| Input | Field | Type |
|---|---|---|
| Bruto jaarloon (EUR) | 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) |
|---|---|---|
| Box 1 belasting | box1Tax | ($g := grossAnnual; $round((($g < $const.band1 ? $g : $const.band1) * $const.rate1) + (($g > $const.band1 ? (($g < $const.band2 ? $g : $const.band2) - $const.band1) : 0) * $const.rate2) + (($g > $const.band2 ? ($g - $const.band2) : 0) * $const.rate3), 2)) |
| Algemene heffingskorting | ahk | (grossAnnual <= 28406 ? 3068 : grossAnnual >= $const.band2 ? 0 : $round(3068 - 0.06337 * (grossAnnual - 28406), 2)) |
| Arbeidskorting | arbeidskorting | (grossAnnual <= 43071 ? 5599 : ($a := 5599 - 0.0651 * (grossAnnual - 43071); $round($a > 0 ? $a : 0, 2))) |
| Belasting | tax | ($x := box1Tax - ahk - arbeidskorting; $round($x > 0 ? $x : 0, 2)) |
| Netto / jaar | netAnnual | $round(grossAnnual - tax, 2) |
| Netto / maand | 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 |
|---|---|
band1 | 38441 |
band2 | 76817 |
rate1 | 0.3582 |
rate2 | 0.3748 |
rate3 | 0.495 |
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 40,000 EUR
given grossAnnual | 40000 |
|---|---|
expect box1Tax | 14353.88 |
expect ahk | 2333.29 |
expect arbeidskorting | 5599 |
expect tax | 6421.59 |
expect netAnnual | 33578.41 |
Case 2 — S3 120,000 EUR — credits fully phased out
given grossAnnual | 120000 |
|---|---|
expect box1Tax | 49528.48 |
expect ahk | 0 |
Sources
- Belastingdienst — tarieven box 1 · 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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