Do I need to register for GST?

Working out your GST turnover

You are not registered for GST, you must check each month to see whether you have reached the GST turnover threshold. If you reach the threshold, you must register for GST within 21 days.

You reach the GST turnover threshold if either:

• your turnover for the current month and the previous 11 months is $75,000 or more - current GST turnover, or
• your turnover for the current month and the next 11 months is likely to be $75,000 or more - projected GST turnover.

However, if your current GST turnover reaches or exceeds the GST turnover threshold, but we are satisfied that your projected turnover will be below the threshold, you do not have to register for GST.

https://www.ato.gov.au/Business/GST/Registering-for-GST/

GST turnover excludes sales not connected with Australia