Open sandbox

How the United Kingdom holiday entitlement calculator is verified

Inputs

InputFieldType
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 you work per weekdaysPerWeeknumber
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)
Weeks EntitlementweeksEntitlement$const.statutoryWeeks
Full Year DaysfullYearDays($raw := weeksEntitlement * daysPerWeek; $raw > $const.daysCap ? $const.daysCap : $raw)
Year Length DaysyearLengthDays$proRataDays(leaveYearStart, leaveYearEnd)
Present DayspresentDays$proRataDays(workStart, workEnd)
Accrual FractionaccrualFraction($f := presentDays / yearLengthDays; $f > 1 ? 1 : $f)
Days EntitleddaysEntitled$round(fullYearDays * accrualFraction, 1)
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
statutoryWeeks5.6
daysCap28

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 — A1 three days a week is 16.8 days (GOV.UK’s own worked example)

given leaveYearStart2026-01-01
given leaveYearEnd2026-12-31
given workStart2026-01-01
given workEnd2026-12-31
given daysPerWeek3
given daysTaken0
expect daysEntitled16.8

Case 2 — A2 a five-day week is the familiar 28 days

given leaveYearStart2026-01-01
given leaveYearEnd2026-12-31
given workStart2026-01-01
given workEnd2026-12-31
given daysPerWeek5
given daysTaken0
expect weeksEntitlement5.6
expect daysEntitled28

Case 3 — A3 the cap bites on a six-day week: 33.6 would be wrong

given leaveYearStart2026-01-01
given leaveYearEnd2026-12-31
given workStart2026-01-01
given workEnd2026-12-31
given daysPerWeek6
given daysTaken0
expect fullYearDays28
expect daysEntitled28

Case 4 — A4 half a leave year on a five-day week

given leaveYearStart2026-01-01
given leaveYearEnd2026-12-31
given workStart2026-01-01
given workEnd2026-06-30
given daysPerWeek5
given daysTaken0
expect presentDays181
expect yearLengthDays365
expect daysEntitled13.9

Case 5 — A5 days already taken come off the remainder

given leaveYearStart2026-01-01
given leaveYearEnd2026-12-31
given workStart2026-01-01
given workEnd2026-12-31
given daysPerWeek5
given daysTaken8
expect daysEntitled28
expect daysRemaining20

Case 6 — A6 taking more than the entitlement never goes negative

given leaveYearStart2026-01-01
given leaveYearEnd2026-12-31
given workStart2026-01-01
given workEnd2026-12-31
given daysPerWeek5
given daysTaken40
expect daysRemaining0

Case 7 — A7 joining partway through the leave year

given leaveYearStart2026-01-01
given leaveYearEnd2026-12-31
given workStart2026-07-01
given workEnd2026-12-31
given daysPerWeek5
given daysTaken0
expect presentDays184
expect daysEntitled14.1

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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