The deadline IS 31 October unless you are lodging through a tax agent, who has an extended lodgement program, however it is unlikely you will cop a penalty.

The ATO has said that if you lodge voluntarily and are not payable, they will not issue a penalty.

Generally the only people who get a penalty are serial offenders or have not complied with a request to lodge.

But if you are worried you can always either ring the ATO and ask for an extension or get a tax agent to put you on their list.