Whilst holiday entitlement calculations aren’t as straightforward for part-time employees as they are for full-time employees, they need not be over complicated and certainly shouldn't be worried about.
A part-time employee is pro-rated to a full-time employee’s entitlement based around a working week. To calculate their holiday entitlement, apply the simplest of simple formulas: 5.6 days x number of working days in a week = holiday entitlement.
The 5.6 figure is based on a statutory entitlement of 28-days, however more days can be given. Should, for example, 33-days be provided the difference to the calculation is 6.6 days x the number of working days in a week = holiday entitlement.
Achieving the 5.6 and 6.6 figure is really easy to understand. If annual leave is 28-days, divide this by the number of working days in the week for a full-time equivalent, i.e., 5. (28/5=5.6) Apply the same calculation for 33-days: (33/5=6.6)
By law leave cannot round down leave – conversely it doesn’t have to be rounded up, but it can be if preferred. As an example, 13.2 days (for an employee who works 2-days a week and has 33-days full time equivalent leave) can be rounded up to 13.5 but it can’t be rounded down to 13.
Sometimes holiday entitlement is expressed by hours for part-time employees. A part-time worker that works 20-hours each week is entitled to the full-time employee’s equivalent of 33-days per annum including bank holidays, albeit on a pro-rata basis. The calculation here would be 20 (hours worked per week) x 6.6 = 132 hours holiday per year. Apply the same principle if annual leave is 28-days per annum, including bank holidays.