When a supply happens within a single state (an intra-state supply), GST is split into two equal components: CGST (Central GST), which goes to the central government, and SGST (State GST), which goes to the state government. For example, an 18% intra-state supply is billed as 9% CGST plus 9% SGST.
The split is automatic in correct billing software and is driven by the place-of-supply rules — not merely by where the seller is registered.
Both halves are computed on the same taxable value at the same moment, not one on top of the other. On a ₹40,000 intra-state supply taxed at 18%, the invoice shows ₹3,600 of CGST and ₹3,600 of SGST, taking the total to ₹47,200. In union territories without their own legislature, UTGST stands in for SGST and behaves identically. The two components are levied under separate enactments, which is why they appear as distinct lines rather than one merged tax.
The split matters most on the credit side. CGST credit can be used only against CGST liability and SGST credit only against SGST — cross-utilisation between the two is barred, and the return system will not permit it. IGST credit, by contrast, can be applied to either. A business can therefore hold surplus credit in one component while owing cash in the other, which is a timing cost rather than an error, but one worth planning around.
Practitioner errors cluster in predictable places: picking the tax head from the customer's billing address rather than the place of supply, rounding each component separately so the two halves drift apart by a paisa, and posting both components to one ledger account so returns cannot be traced back to the books. Clean practice keeps four accounts — output and input, for CGST and for SGST — so every figure in a return has a matching trail in the ledger.