How to Pro-Rata a new employee

[Mel17]

Hello all,
Hope someone can help me... I've recently started work again after having my little one and the job I have is in HR but also includes payroll (I have no experience in payroll!!) anyways I have a new employee to process and need some help on how to pro rata the salary for them. The employee in question will be working 16hours a week (three weekdays) and then the following week 16 hours plus the Saturday for 5 hours. Then she'll revert back to just the three days then back to 22 hours etc. would anyone know how I would calculate her annual salary??
Many thanks to anyone that can help.

I have one member staff who does similar we do average hours so for your employee 19 hours per week and pay salary on this. We calculate holiday in hours based in 19 hours per week.

When I did this kind of working pattern they based it on annual hours.

There are 52 weeks in a year, and she's alternating 16 hours and 22 hours a week. 26x16=416 26x22=572. Add the two together and that's her annual total- 988 hours. So her annual salary is whatever her hourly rate is multiplied by 988.