How the Netherlands motorrijtuigenbelasting calculator is verified
Inputs
| Input | Field | Type |
|---|---|---|
| Gewicht (kg) | weight | number |
| Brandstof (0 benzine, 1 diesel, 2 elektrisch) | fuel | 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) |
|---|---|---|
| Tarief per 100 kg | ratePer100 | fuel = 1 ? $const.dieselPer100 : $const.petrolPer100 |
| Basis MRB | baseMrb | $round(weight / 100 * ratePer100, 2) |
| MRB per jaar | mrb | $round(fuel = 2 ? baseMrb * $const.evDiscount : baseMrb, 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 |
|---|---|
petrolPer100 | 24 |
dieselPer100 | 115 |
evDiscount | 0.7 |
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 — C1 petrol 1,100 kg
given weight | 1100 |
|---|---|
given fuel | 0 |
expect ratePer100 | 24 |
expect baseMrb | 264 |
expect mrb | 264 |
Case 2 — C3 electric 2,100 kg — weight base minus discount
given weight | 2100 |
|---|---|
given fuel | 2 |
expect baseMrb | 504 |
expect mrb | 352.8 |
Sources
- Belastingdienst — MRB berekenen · 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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