Contract invoicing and commission calculations are done from the Timesheet form on a timesheet-by-timesheet basis.
The commission calculations are performed for a Timesheet the same way you do for a permanent placement on the Vacancies form.
When Timesheet commissions are calculated for the first time (by pressing the Calculate Commissions button or using the Timesheets Tool) the Consultants list from the related vacancy is copied to the timesheet. For this reason you should enter contract consultants and their Bills percentage on the Vacancies form since it saves having to manually reenter the information every time a new timesheet is created.
By way of example, a timesheet for 50 hours work is billed out at a contractor rate of $40 per hour and a client rate of $50 per hour. Two consultants are involved: Joe (whose contract commission rate is 25%) Bills 75% of the vacancy and Mary (whose contract commission rate is 40%) bills the remaining 25%:
Total Billings $500 (50 hours multiplied by $10 ($50 minus $40))
Joe's Billings $375 (75% of $500 total billings)
Joe's Commission $93.75 (25% of his $375 billings)
Mary's Billings $125 (25% of $500 total billings)
Mary's Commission $50 (40% of her $125 billings)