Pro rata holiday is the entitlement scaled to the part of it a person is actually owed: a part-timer's share of a full-timer's year, or a starter's share of the leave year that is left. Both are the same operation and both are where a small employer's spreadsheet most often goes wrong, because the temptation is to scale a remembered number rather than the pattern. This page shows how to calculate pro rata holiday the way the free annual leave calculator on this site does it, with the two cases kept apart: pro rata for hours, and pro rata for time.
Pro rata for part-timers: scale the weeks, not the days
A part-timer gets the same 5.6 weeks as everyone else; what changes is how many days are in their week. Three days a week times 5.6 is 16.8 days, and that is the whole calculation. Do not take a full-timer's 28 days and multiply by three fifths, because as soon as the contract gives more than the minimum, or bank holidays are counted inside, the shortcut and the real figure diverge. The pro rata leave calculator on this site takes days a week as the input for exactly this reason.
The pro rata leave calculator for starters and leavers: scale by the year left
Someone joining with nine months of the leave year to run gets nine twelfths of the full-year figure: 16.8 days on a three-day week becomes 12.6. Counting in days rather than months is more precise and the difference matters for a leaver, whose untaken balance is paid in the final pay. The annual leave calculator pro rata option on this site asks for the months employed and returns the pro rata figure next to the full-year one so both are visible.
Rounding: up, never down, and only at the end
Pro rata figures come out fractional, and the rule is to round in the worker's favour and only once, at the end of the calculation. 12.6 days is 12.6 days; a half day is a sensible unit to book in and the policy template on this site states the unit. Rounding 16.8 to 16 before scaling, then 12 after, hands a part-timer a day less than they are owed and is the kind of thing that surfaces in a grievance rather than a spreadsheet.
Bank holidays on a pro rata basis
If the policy counts bank holidays inside the 5.6 weeks, a part-timer's share of them is already in the 16.8 days and nothing more is owed. If the policy gives bank holidays on top, a part-timer who never works Mondays would get fewer than a colleague who does, so the fair approach is to give a pro rata share of the bank holidays as days to book. The separate page on whether 28 days includes bank holidays sets out both shapes.
Questions people ask about pro rata holiday calculator UK
How to calculate pro rata holiday for a part-time employee?
Multiply their days a week by the weeks of leave, with 5.6 weeks as the statutory floor. Two days a week gives 11.2 days. Use hours a week times 5.6 where their days vary.
How do I calculate pro rata holiday for a new starter?
Work out the full-year figure from their pattern, then scale it by the part of the leave year left from their start date. Nine months of twelve on 16.8 days is 12.6 days.
Should pro rata holiday be rounded?
Round in the worker's favour and only at the end. Keep fractions of a day in the record; a half day is a practical booking unit and the policy can say so.
Do part-timers get pro rata bank holidays?
If bank holidays are counted inside the statutory 5.6 weeks, their share is already in the entitlement. If they are given on top, a pro rata share avoids the Monday problem where one part-timer benefits and another does not.