Add 10% GST to a price, or pull the GST back out of a total. Updates as you type.
Australian GST is 10%. Results appear as you type.
To find the GST inside a price, you divide by 11 — you do not take 10% off.
GST is 10% of the pre-GST price, so a GST-inclusive total is 11⁄10 of that price. The GST portion is therefore exactly one eleventh of the total. Take 10% off $110 and you get $99, which is wrong by a dollar; divide $110 by 11 and you get the real $10 of GST, leaving $100.
The error is small on one invoice and compounds badly across a BAS quarter, which is why it is worth doing the division rather than the subtraction.
Most basic food is GST-free, as are many health, medical and education supplies. Some things are input-taxed instead, which is different again. If you are unsure whether a particular supply carries GST, check the ATO rather than assuming — this tool does the arithmetic, not the classification.