Intra-state supply splits GST equally into CGST and SGST. Inter-state supply is charged as a single IGST. Margin uses the base (ex-GST) amount, since GST is collected on behalf of the government.
How GST splits into CGST, SGST and IGST
India's GST is a single tax collected in one of two ways depending on where the buyer is:
- Intra-state (buyer in your state) → the rate is split equally into CGST (central) and SGST (state). An 18% rate becomes 9% + 9%.
- Inter-state (buyer in another state) → the full rate is charged as one IGST. 18% stays 18% IGST.
The total tax is identical either way — only the split changes. For your margin, what matters is the base (ex-GST) amount: GST is money you collect for the government, not revenue you keep.