This depends on various factors. The easiest way to find out is to contact your tax agent directly and they will be able to provide you with the due date directly from the Australian Taxation Office.
There are various due dates, but if you lodge a tax return through a registered tax agent, you have an extension until the 15th of May. If you are not going to lodge through a registered tax agent, then your tax return will be due on the 31st of October.