If you want to manually calculate accrued holiday allowance, this is how you do it.
Typically the rule is to calculated based on 365 days.
Using 365 days per year as an example for a full time employee, with 28 days' entitlement, who started on 20 February 2017, you would use the following
Allowance earned per day: 28/365 = 0.0767 days
To find out the actual accrued allowance for the year you would use the following calculation:
Total 2017 Entitlement: 0.0767(Allowance earned per day) * 315(amount of days from start date to end of the year) = 24.16 days.
**please note employees will still accrue holiday if they are on Maternity leave, sickness or on holiday.**