How the New Zealand rego & ruc calculator is verified
Inputs
| Input | Field | Type |
|---|---|---|
| Fuel type | fuel | string |
| Annual distance (km) | km | 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) |
|---|---|---|
| RUC rate per 1,000 km | rucRate | ($f := fuel; $f = 'diesel' or $f = 'ev' ? $const.rucPer1000 : $f = 'phev' ? $const.rucPhevPer1000 : 0) |
| Road User Charges | ruc | $round(km / 1000 * rucRate, 2) |
| Annual total | total | $round($const.rego + ruc, 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 |
|---|---|
rego | 107 |
rucPer1000 | 76 |
rucPhevPer1000 | 38 |
Test vectors (4)
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 car — licence only, no RUC
given fuel | petrol |
|---|---|
given km | 0 |
expect rucRate | 0 |
expect ruc | 0 |
expect total | 107 |
Case 2 — C2 diesel, 12,000 km — RUC plus licence
given fuel | diesel |
|---|---|
given km | 12000 |
expect rucRate | 76 |
expect ruc | 912 |
expect total | 1019 |
Case 3 — C3 electric, 12,000 km — same RUC as diesel since 1 July 2026
given fuel | ev |
|---|---|
given km | 12000 |
expect ruc | 912 |
expect total | 1019 |
Case 4 — C4 plug-in hybrid, 12,000 km — half the RUC rate
given fuel | phev |
|---|---|
given km | 12000 |
expect rucRate | 38 |
expect ruc | 456 |
expect total | 563 |
Sources
- NZTA — rego & RUC · 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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