Open sandbox

How the Netherlands vakantie-uren calculator is verified

Inputs

InputFieldType
Agreed hours per weekhoursPerWeeknumber
Days you spread them overdaysPerWeeknumber
Leave year starts (YYYY-MM-DD)leaveYearStartstring
Leave year ends (YYYY-MM-DD)leaveYearEndstring
First day worked in it (YYYY-MM-DD)workStartstring
Last day worked in it (YYYY-MM-DD)workEndstring
Days already takendaysTakennumber

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)
Hours Per DayhoursPerDay($d := $n(daysPerWeek); $d > 0 ? $n(hoursPerWeek) / $d : 0)
Hours Entitled FullhoursEntitledFull$const.statutoryWeeks * $n(hoursPerWeek)
Year Length DaysyearLengthDays$proRataDays(leaveYearStart, leaveYearEnd)
Present DayspresentDays$proRataDays(workStart, workEnd)
Accrual FractionaccrualFraction($f := presentDays / yearLengthDays; $f > 1 ? 1 : $f)
Hours EntitledhoursEntitled$round(hoursEntitledFull * accrualFraction, 2)
Days EntitleddaysEntitled(hoursPerDay > 0 ? $round(hoursEntitled / hoursPerDay, 1) : 0)
Days RemainingdaysRemaining($r := daysEntitled - $n(daysTaken); $r < 0 ? 0 : $round($r, 1))

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
statutoryWeeks4

Test vectors (7)

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 — H1 40 hours over five days: 160 hours, which is the familiar 20 days

given hoursPerWeek40
given daysPerWeek5
given leaveYearStart2026-01-01
given leaveYearEnd2026-12-31
given workStart2026-01-01
given workEnd2026-12-31
given daysTaken0
expect hoursEntitledFull160
expect hoursEntitled160
expect daysEntitled20

Case 2 — H2 36 hours over four days: 144 hours and 16 days — still four weeks, not 20 days

given hoursPerWeek36
given daysPerWeek4
given leaveYearStart2026-01-01
given leaveYearEnd2026-12-31
given workStart2026-01-01
given workEnd2026-12-31
given daysTaken0
expect hoursEntitledFull144
expect hoursPerDay9
expect daysEntitled16

Case 3 — H3 24 hours over three days: 96 hours and 12 days

given hoursPerWeek24
given daysPerWeek3
given leaveYearStart2026-01-01
given leaveYearEnd2026-12-31
given workStart2026-01-01
given workEnd2026-12-31
given daysTaken0
expect hoursEntitled96
expect daysEntitled12

Case 4 — H4 half a leave year, pro-rated by lid 2

given hoursPerWeek40
given daysPerWeek5
given leaveYearStart2026-01-01
given leaveYearEnd2026-12-31
given workStart2026-01-01
given workEnd2026-06-30
given daysTaken0
expect presentDays181
expect hoursEntitled79.34
expect daysEntitled9.9

Case 5 — H5 a period wider than the leave year manufactures nothing

given hoursPerWeek40
given daysPerWeek5
given leaveYearStart2026-01-01
given leaveYearEnd2026-12-31
given workStart2020-01-01
given workEnd2030-12-31
given daysTaken0
expect accrualFraction1
expect daysEntitled20

Case 6 — H6 days already taken come off the remainder

given hoursPerWeek40
given daysPerWeek5
given leaveYearStart2026-01-01
given leaveYearEnd2026-12-31
given workStart2026-01-01
given workEnd2026-12-31
given daysTaken8
expect daysRemaining12

Case 7 — H7 taking more than the entitlement never goes negative

given hoursPerWeek40
given daysPerWeek5
given leaveYearStart2026-01-01
given leaveYearEnd2026-12-31
given workStart2026-01-01
given workEnd2026-12-31
given daysTaken50
expect daysRemaining0

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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