The agent will deduct withholding tax from your wages which is normally 20%. The tax will be returned to IRD within their PAYE return. You also can find the figure from you IRD account once your agent file the return. By the end of 31 Mar 2012, you are required to file IR3 return and declare the expenses you need to claim. IRD will work out what you should pay/refund for your tax from there.