If you meet the criteria and are required to be registered for GST and you don’t register, the ATO can impose penalties including:

• backdating the registration to the date you should have registered – this could mean having to pay GST on all sales back to this date (even if you didn’t specifically add GST to those sales amounts);
• failure to lodge penalties for the late lodgement of activities statements;
• interest charges on payments that are late as a result of the late registration.