How the Italy bollo auto calculator is verified

Inputs

Input	Field	Type
Potenza (kW)	`kw`	number
Regione	`regione`	string
Coefficiente se « Altra » (es. 1.00)	`customFactor`	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)
Coefficiente regionale	`regionFactor`	`($r := regione; $r = 'standard' ? $const.factorStandard : $r = 'emilia' ? $const.factorEmiliaRomagna : $r = 'toscana' ? $const.factorToscana : $r = 'abruzzo' ? $const.factorAbruzzoCampania : $r = 'bolzano' ? $const.factorBolzano : customFactor)`
Bollo	`bollo`	`($k := kw; $b := $k <= $const.kwThreshold ? $k * $const.rateLow : $const.kwThreshold * $const.rateLow + ($k - $const.kwThreshold) * $const.rateHigh; $round($b * regionFactor, 2))`
Superbollo (oltre 185 kW)	`superbollo`	`$round(kw > $const.superThreshold ? (kw - $const.superThreshold) * $const.superRate : 0, 2)`
Bollo annuo	`total`	`$round(bollo + superbollo, 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
`rateLow`	2.58
`rateHigh`	3.87
`kwThreshold`	100
`superThreshold`	185
`superRate`	20
`factorStandard`	1
`factorEmiliaRomagna`	1.1
`factorToscana`	1.05
`factorAbruzzoCampania`	1.21
`factorBolzano`	0.76

Test vectors (3)

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 88 kW petrol

given `kw`	88
given `regione`	standard
expect `bollo`	227.04
expect `superbollo`	0
expect `total`	227.04

Case 2 — C3 200 kW — bollo plus superbollo

given `kw`	200
given `regione`	standard
expect `bollo`	645
expect `superbollo`	300
expect `total`	945

Case 3 — C2 88 kW immatricolata in Emilia-Romagna — +10% dal 2026

given `kw`	88
given `regione`	emilia
expect `regionFactor`	1.1
expect `bollo`	249.74
expect `total`	249.74

Sources

Calcolo bollo — ACI · 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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