Nobody gets the salary wrong
Pro rata pay is a fraction. 22.5 hours against a 37.5 hour week is 60%, so £40,000 becomes £24,000. Use hours rather than days, because days stop working the moment somebody has a pattern of long and short ones.
The holiday is where it goes wrong. Specifically the bank holidays, and specifically in a way that lands on the same people every single year.
The Monday problem
Most bank holidays fall on a Monday. In England and Wales in 2026 it is five of the eight, plus two Fridays and a Thursday. So if the business simply closes on bank holidays and everybody "gets the bank holidays":
| One day a week, same hours | Bank holidays received |
|---|---|
| Works Mondays | 5 |
| Works Thursdays | 1 |
Identical contracts, identical hours, identical employer, and a four day gap. Neither of them has done anything and the pro rata entitlement for both is about 1.6 days. The effect is sharpest on the smallest contracts, which is to say on the people least able to absorb it.
It is not a one-off either. The bank holidays are on the same weekdays for structural reasons, so whoever works Mondays wins every year and whoever works Thursdays loses every year.
Which is a legal problem, not just an unfair one
The Part-time Workers (Prevention of Less Favourable Treatment) Regulations 2000 stop a part-time worker being treated less favourably than a comparable full-timer on the ground of being part time, unless it can be objectively justified. A rule that reads as neutral and falls unevenly is the textbook shape, and "the bank holidays happen to fall on days you do not work" is precisely that.
The fix is one line of policy
Give every part-timer a pro rata number of bank holiday HOURS, added to their entitlement, and let them take the days off whenever they fall. Somebody on 60% of full-time hours gets 60% of the bank holiday hours a full-timer receives. It no longer matters which days they work.
That is it. It is well established, it costs nothing to administer once the entitlement is held in hours, and it is rarely applied. Tick the pro rata box in the tool and watch the entitlement stop depending on the calendar.
Do not pro rata the 28 day cap
Statutory holiday is 5.6 weeks, capped at 28 days. Two things follow that are regularly got wrong:
- The cap only bites at five days a week and above. It is why a full-timer gets 28 rather than 5.6 times 5, and why somebody working six days still gets 28 rather than 33.6.
- Below five days it never applies. A three day worker is entitled to the full 16.8 days, not to a scaled-down version of 28.
Pro rating the cap instead of the weeks produces 16.8 either way at three days, and starts shorting people as soon as the pattern is unusual. It is a small error that repeats annually.
Hold the entitlement in hours
Everything above is calculated in hours and converted to days only for display, and that is not a stylistic choice. Hours are the only unit that survives a mixture of long and short days, somebody changing their hours in July, or an irregular pattern with no fixed days at all.
Days are a good way to tell somebody what they have got. They are a bad way to hold it, because every awkward case breaks them and the awkward cases are exactly the people this all falls on.
Common questions
How do I work out a pro rata salary?
Divide the part-time hours by the full-time hours and multiply the full-time salary by the result. 22.5 hours against 37.5 is 60%, so £40,000 becomes £24,000. Use hours rather than days, because days break as soon as somebody works a pattern of long and short ones. Almost nobody gets the salary wrong. What goes wrong is the holiday, and specifically the bank holidays.
Why do part-timers lose out on bank holidays?
Because most bank holidays fall on a Monday. In England and Wales in 2026 it is five of the eight, with two Fridays and a Thursday. If the business simply closes and everybody "gets the bank holidays", a Monday worker collects five paid days and a Thursday worker collects one, out of an identical entitlement. Neither has done anything. The calendar has done it, and it does the same thing every year to the same people.
How should bank holidays be handled for part-time staff?
Give every part-timer a pro rata number of bank holiday hours added to their entitlement, and let them take the days off whenever they fall. Somebody on 60% of full-time hours gets 60% of the bank holiday hours a full-timer receives, regardless of which days they work. It is well established, it is simple, and it is rarely applied. Ticking the pro rata box in the tool shows the difference it makes.
Is it discrimination to give part-timers fewer bank holidays?
It can be. The Part-time Workers (Prevention of Less Favourable Treatment) Regulations 2000 prevent a part-time worker being treated less favourably than a comparable full-timer on the ground of being part time, unless it is objectively justified. A rule that looks neutral and lands unevenly is the textbook shape of the problem, and "the bank holidays happen to fall on days you do not work" is exactly that. The hours-based approach removes the issue rather than defending it.
Do I pro rata the 28 day holiday cap?
No. It is a common and expensive error. Statutory holiday is 5.6 weeks capped at 28 days. The cap only bites at five days a week and above, which is why a full-timer gets 28 rather than 5.6 times 6, and why somebody on six days a week still gets 28. Below five days the cap never applies at all, so a three day worker is entitled to the full 16.8 days. Pro rating the cap instead of the weeks shorts part-timers by a day or two every year.
Should holiday be held in days or hours?
Hours. Days are fine for telling somebody what they have got and they are a bad unit to hold the entitlement in, because they break the moment somebody works long and short days, changes their hours mid year, or has an irregular pattern. Hours survive all three. Work in hours and convert to days for the conversation.
Does the nation change the answer?
Yes. Scotland and Northern Ireland have different bank holidays from England and Wales, both in number and in which days they land on, so both the entitlement and the Monday problem change with the nation. The tool computes the dates rather than looking them up, so any year works and the answer follows whichever nation you pick.