How the Türkiye kdv (vat) calculator is verified

Inputs

InputFieldType
Amountamountnumber
Directiondirectionstring
What is being suppliedcategorystring
B2B reverse charge appliesreverseChargeboolean

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)
Rateratecategory = 'reduced1' ? $const.reducedRate1 : category = 'superReduced' ? $const.superReducedRate : $const.standardRate
Effective RateeffectiveRatereverseCharge ? 0 : rate
Net AmountnetAmountdirection = 'remove' ? $round(amount / (1 + effectiveRate), 2) : $round(amount, 2)
Vat AmountvatAmount$round(netAmount * effectiveRate, 2)
Gross AmountgrossAmount$round(netAmount + vatAmount, 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
standardRate0.2
superReducedRate0.01
reducedRate10.1

Test vectors (5)

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 — S1 100.00 TRY net at the genel oran

given amount100
given directionadd
given categorystandard
given reverseChargeno
expect vatAmount20
expect grossAmount120
expect netAmount100

Case 2 — S2 120.00 TRY gross back to net at %20

given amount120
given directionremove
given categorystandard
given reverseChargeno
expect netAmount100
expect vatAmount20

Case 3 — S3 100.00 TRY net at %10

given amount100
given directionadd
given categoryreduced1
given reverseChargeno
expect vatAmount10
expect grossAmount110

Case 4 — S4 100.00 TRY of basic food at %1

given amount100
given directionadd
given categorysuperReduced
given reverseChargeno
expect vatAmount1
expect grossAmount101

Case 5 — S5 reverse charge: the supplier charges no KDV

given amount100
given directionadd
given categorystandard
given reverseChargeyes
expect vatAmount0
expect grossAmount100

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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