There should be some websites in here to help you:
http://www.google.com/search?q=payroll+tax+formulas+WI&rls=com.microsoft:en-us:IE-SearchBox&ie=UTF-8&oe=UTF-8&sourceid=ie7&rlz=1I7SUNA
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project is to calculate payroll. I have the gross earnings, what percentages are used to calculate FICA, Fed and WI state taxes per pay-week?