What Do I Charge GST On?
You are liable to charge GST if you are registered, or required to be registered, and you make a taxable supply.
You make a taxable supply when:
you are registered or required to be registered;
you make a supply for consideration;
the supply is connected with Australia;
the supply is not GST-free or input-taxed
The definition of supply catches just about everything, so unless you’re making a GST-free supply or an input-taxed supply, and you are registered, then you most likely have to charge GST.
To work out the amount of GST you would charge, you add 10% of the sale price.