How do I work out holiday entitlement for part-time and irregular-hours staff?

The answer Just Ask, HR gives

Detailed Dan — Structured and thorough — every step in order.

Three worker types, three calculations — all flowing from one rule: everyone gets 5.6 weeks' paid holiday a year (capped at 28 days), where a "week" means their working week.

1. Full-timers (5 days/week): 5.6 × 5 = 28 days. Bank holidays can be counted within it (check what your contract promises).

2. Regular part-timers: same formula, their week. Your 3-day bookkeeper: 5.6 × 3 = 16.8 days. Don't round down — 16.8 means 16.8 (round up to 17 if you want cleaner admin; never down). Bank holiday fairness tip: pro-rate the bank-holiday allowance rather than letting entitlement hinge on whether their working days happen to fall on Mondays.

3. Irregular-hours and part-year workers (your weekend casuals): for leave years starting on or after 1 April 2024, the law restored the 12.07% accrual method — they accrue holiday at 12.07% of hours actually worked in each pay period. Work 40 hours in a month → accrue 4.83 hours of holiday. (Why 12.07%? 5.6 weeks ÷ 46.4 working weeks.) You may also lawfully pay rolled-up holiday pay for these workers: a 12.07% uplift itemised separately on each payslip — the cleanest option for genuinely casual staff, but it must be visible on the payslip, not buried in the rate.

Holiday pay rate traps: regular overtime, commission and shift premiums must be included in holiday pay for at least the 4 weeks of "Euro-leave" — and for irregular-hours workers, use the 52-week average of paid weeks. Basic-pay-only holiday pay for staff with regular overtime is the classic quiet liability.

Put each person's calculation in writing once — the arguments usually dissolve when people see their own maths.