How the Ireland motor tax calculator is verified
Inputs
| Input | Field | Type |
|---|---|---|
| CO₂ emissions (g/km) | co2 | 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) |
|---|---|---|
| Annual motor tax | tax | ($c := co2; $round($c = 0 ? 120 : $c <= 50 ? 140 : $c <= 80 ? 150 : $c <= 90 ? 160 : $c <= 100 ? 170 : $c <= 110 ? 180 : $c <= 120 ? 190 : $c <= 130 ? 200 : $c <= 140 ? 210 : $c <= 155 ? 270 : $c <= 170 ? 280 : $c <= 190 ? 400 : $c <= 225 ? 790 : 2400, 2)) |
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 100 g/km
given co2 | 100 |
|---|---|
expect tax | 170 |
Case 2 — C2 140 g/km
given co2 | 140 |
|---|---|
expect tax | 210 |
Sources
- Motor tax rates (motortax.ie) · 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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