How the Netherlands zzp calculator is verified

Inputs

Input	Field	Type
Annual profit after expenses (EUR)	`annualProfit`	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)
After Self Employed Deduction	`afterSelfEmployedDeduction`	`$round($max([0, annualProfit - $const.selfEmployedDeduction]), 2)`
Taxable profit	`taxableProfit`	`$round(afterSelfEmployedDeduction * (1 - $const.mkbExemption), 2)`
Box 1 income tax	`incomeTax`	`$round($const.band1Rate * $min([taxableProfit, $const.band1Limit]) + $const.band2Rate * $max([0, $min([taxableProfit, $const.band2Limit]) - $const.band1Limit]) + $const.band3Rate * $max([0, taxableProfit - $const.band2Limit]), 2)`
Zvw healthcare contribution	`healthcareContribution`	`$round($min([taxableProfit, $const.zvwCeiling]) * $const.zvwRate, 2)`
Net income / year (before credits)	`netIncome`	`$round($max([0, annualProfit - incomeTax - healthcareContribution]), 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
`selfEmployedDeduction`	1200
`mkbExemption`	0.127
`band1Limit`	38883
`band2Limit`	78426
`band1Rate`	0.3575
`band2Rate`	0.3756
`band3Rate`	0.495
`zvwRate`	0.0485
`zvwCeiling`	79409

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 — 60,000 EUR profit — a typical full-time zzp-er, into the second box 1 band

given `annualProfit`	60000
expect `afterSelfEmployedDeduction`	58800
expect `taxableProfit`	51332.4
expect `incomeTax`	18576.67
expect `healthcareContribution`	2489.62
expect `netIncome`	38933.71

Case 2 — 25,000 EUR profit — part-time, first band only

given `annualProfit`	25000
expect `afterSelfEmployedDeduction`	23800
expect `taxableProfit`	20777.4
expect `incomeTax`	7427.92
expect `healthcareContribution`	1007.7
expect `netIncome`	16564.38

Case 3 — 120,000 EUR profit — top band, and Zvw stops at the ceiling

given `annualProfit`	120000
expect `taxableProfit`	103712.4
expect `healthcareContribution`	3851.34

Sources

KVK — Belastingtarieven 2026: box 1 schijven, zelfstandigenaftrek 1.200 EUR, mkb-winstvrijstelling 12,7%, Zvw 4,85% tot 79.409 EUR · checked 2026-08-22
Belastingdienst — Inkomensafhankelijke bijdrage Zvw (grondslag = belastbare winst) · checked 2026-08-22

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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