The system handles both of these simply and efficiently, calculating both automatically, where appropriate.
Basically, if you enter a GST number in the GST field in the crew/cast Masterfile, the system will automatically calculate the correct GST on their fees etc in “Pay Wages”.
For withholding tax, you just need to enter the required % (usually 20%) in the Flat Rate field in the Taxation tab and “WT” as the tax code when setting up and crew/cast (NB no withholding tax for cast or crew engaged through loan-outs – so tax code = “C” for Company)
Under “All employees”, there is an “IR348 Export” function which allows you to export all the gross fees paid and withholding tax deducted for every cast/crew member (i.e. who has tax code “WT”) for a particular month. You can then upload this file into the IRD’s website for the required monthly employer reporting. Payments to loan-outs are not required to be reported to the IRD.