How the Estonia car tax calculator is verified

Inputs

Input	Field	Type
CO₂ emissions (g/km, WLTP)	`co2`	number
Gross mass (kg)	`mass`	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)
CO₂ over 117 g/km	`co2Over`	`($x := co2 - $const.co2Free; $round($x > 0 ? $x : 0, 2))`
Mass Over	`massOver`	`($x := mass - $const.massFree; $round($x > 0 ? $x : 0, 2))`
Annual CO₂ component	`annualCo2`	`$round($const.annualCo2Rate * co2Over, 2)`
Annual weight component	`annualWeight`	`$round($const.annualMassRate * massOver, 2)`
Annual tax	`annualTax`	`$round($const.annualBase + annualCo2 + annualWeight, 2)`
Reg Co2	`regCo2`	`$round($const.regCo2Rate * co2Over, 2)`
Registration (one-time)	`registrationTax`	`$round($const.regBase + regCo2, 2)`
First-year total	`firstYearTotal`	`$round(annualTax + registrationTax, 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
`co2Free`	117
`massFree`	2000
`annualBase`	50
`annualCo2Rate`	3
`annualMassRate`	0.2
`regBase`	300
`regCo2Rate`	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 — 150 g/km, 1800 kg

given `co2`	150
given `mass`	1800
expect `co2Over`	33
expect `annualTax`	149
expect `registrationTax`	465
expect `firstYearTotal`	614

Case 2 — 95 g/km (below CO2 threshold), 2500 kg heavy

given `co2`	95
given `mass`	2500
expect `co2Over`	0
expect `annualWeight`	100
expect `annualTax`	150
expect `registrationTax`	300
expect `firstYearTotal`	450

Sources

EMTA — vehicle tax calculator · 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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