How GST is calculated
To add GST: GST amount = price × rate ÷ 100, and total = price + GST.
To remove GST from a price that already includes it: price without GST = total × 100 ÷ (100 + rate), and GST = total − price without GST.
Example: a ₹10,000 item at 18% GST has ₹1,800 GST, so the total is ₹11,800. If ₹11,800 is the final price, removing 18% gives ₹10,000 plus ₹1,800 GST.
CGST, SGST and IGST
For a sale within one state, the GST is split equally into CGST (to the Centre) and SGST (to the state). For a sale between states, the full amount is charged as IGST.
Common questions
Is GST charged on the selling price or the cost? On the transaction value, which is normally the selling price you invoice.
Do I need to charge GST? Only if you are registered, or required to register, under GST. See our other tools and guides, and confirm your own case with a CA.