How the South Korea 자동차세 calculator is verified
Inputs
| Input | Field | Type |
|---|---|---|
| 배기량 (cc) | cc | number |
| 차령 (년) | ageYears | 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) |
|---|---|---|
| cc당 세율 (KRW) | rate | ($c := cc; $c <= 1000 ? 80 : $c <= 1600 ? 140 : 200) |
| 차령 경감률 | ageDiscount | ($a := ageYears; $d := $a < $const.discountStartYear ? 0 : ($a - $const.discountStartYear + 1) * $const.discountPerYear; $round($d < $const.maxDiscount ? $d : $const.maxDiscount, 2)) |
| Tax Before Discount | taxBeforeDiscount | $round(cc * rate * (1 + $const.surtax), 2) |
| 연간 자동차세 | tax | $round(taxBeforeDiscount * (1 - ageDiscount), 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 |
|---|---|
surtax | 0.3 |
discountPerYear | 0.05 |
discountStartYear | 3 |
maxDiscount | 0.5 |
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 999 cc
given cc | 999 |
|---|---|
given ageYears | 0 |
expect rate | 80 |
expect tax | 103896 |
Case 2 — C2 1,998 cc new
given cc | 1998 |
|---|---|
given ageYears | 0 |
expect rate | 200 |
expect tax | 519480 |
Case 3 — C3 1,998 cc, 12년 이상 — 최대 50% 경감
given cc | 1998 |
|---|---|
given ageYears | 12 |
expect ageDiscount | 0.5 |
expect tax | 259740 |
Sources
- Wetax — 자동차세 · 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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