HELP please with Variable Holiday Pay

Has anyone please a piece of kit/spreadsheet that can help with HP for variable paid employees. I totally understand the legislation. Im just having difficult operating it in a professional way. Its OK for one employee but variable is just that - missing weeks/months are not the same for everyone and it's a rolling programme. Someone was telling me about "days" worked. I actually cant get my head round 52 weeks when an employee has the hours calculated as a monthly total and not split into weeks.