How the United States registration calculator is verified

Inputs

Input	Field	Type
Vehicle value (USD)	`value`	number
State	`state`	string
Rate if "Other" (fraction, e.g. 0.028)	`customRate`	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)
Rate	`rate`	`($s := state; $s = 'CA' ? $const.rateCA : $s = 'VA' ? $const.rateVA : customRate)`
Annual fee/tax	`tax`	`$round(value * rate, 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
`rateCA`	0.0065
`rateVA`	0.04

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 CA 30,000 USD at 0.65% VLF

given `value`	30000
given `state`	CA
expect `tax`	195

Case 2 — C2 VA 25,000 USD at 2.8% property tax

given `value`	25000
given `state`	other
given `customRate`	0.028
expect `tax`	700

Sources

CA DMV VLF · checked 2026-08-02
Virginia Tax — PPTRA · 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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