IGST (Integrated GST)
The single GST charged when goods move from one state to another, levied at the full rate instead of a CGST and SGST split.
IGST applies when the supplier and the place of supply are in different states or Union Territories. Instead of two half-rate lines, the invoice carries one line at the full rate.
Why one line, not two
Inter-state supply needs the tax to travel with the goods so the consuming state gets its share. IGST is collected by the Centre and apportioned. For you as the seller it simply means one tax line and one rate.
The test is the place of supply
Not where the buyer's office is, and not where the payment came from. For goods it is generally where the movement of the goods ends. A Mumbai buyer asking for delivery to their Pune godown is an intra-state supply for a Maharashtra seller, even though the buyer has offices elsewhere.
Imports and exports
Imports attract IGST. Exports are treated as zero-rated, which is a separate mechanism with its own paperwork — take advice before setting up the invoice format for export sales.
How KillStock handles it
The place of supply on the sale decides whether the document prints IGST or the CGST and SGST pair, and the GST reports keep the components separate. Where a consignment needs an e-way bill, the details for it are prepared from the same sale.
A common mistake
Splitting an inter-state sale into CGST and SGST because the total is the same. It is not the same for your buyer's credit, and it will not reconcile on the portal.