How the Georgia import excise calculator is verified

Inputs

InputFieldType
Engine size (cm³)ccnumber
Car age (years)ageYearsnumber
Fuel factor (1 petrol, 0.5 hybrid, 0 EV)fuelFactornumber

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 valueFieldFormula (JSONata)
Age factor (U-shaped)ageFactor($a := ageYears; $a < 2 ? 1.4 : $a <= 5 ? 1.0 : $a <= 10 ? 1.5 : 2.0)
Import exciseexcise$round(cc * $const.baseRate * ageFactor * fuelFactor, 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.

ConstantValue
baseRate1.5

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 2.0 L petrol, 7 years old

given cc2000
given ageYears7
given fuelFactor1
expect ageFactor1.5
expect excise4500

Case 2 — C3 EV — exempt

given cc0
given ageYears1
given fuelFactor0
expect excise0

Sources

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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