Q.The same dealer, Patel Traders of Ahmedabad, sells goods worth ₹80,000 (before tax) to a buyer in Maharashtra. GST is chargeable at 18%. Compute the tax and the total invoice value.

India's GST is a dual tax — both the Union and the States tax the same supply, because the Constitution gives both levels of government the power to tax goods and services, and neither level was willing (or constitutionally required) to give up that power when GST replaced the older separate taxes.

The structure that results depends on whether a supply is intra-state or inter-state:

• Intra-state supply (buyer and seller in the same state): two taxes are charged together on the same value — CGST, going to the Central Government, and SGST, going to the State Government of that state. They are ordinarily charged at equal rates, so an 18% GST rate typically means 9% CGST + 9% SGST on the invoice.
• Inter-state supply (buyer and seller in different states, or an import into India): a single tax, IGST, is charged instead, collected by the Centre at a rate equal to what CGST + SGST would together have been, and subsequently apportioned between the Centre and the destination state.
• Intra-UT supply (within a Union Territory without its own legislature): UTGST takes the place of SGST, charged alongside CGST, working exactly like the CGST + SGST pair does within a state.

This structure is coordinated across the whole country by the GST Council — chaired by the Union Finance Minister, with every state's Finance Minister as a member — which recommends the rate slabs, exemptions, thresholds and rules that all states and the Centre then apply uniformly. Without a body like the GST Council deciding these matters jointly, a dual GST run by 28+ states and the Centre independently could easily have drifted back into the same fragmented, state-by-state variation that GST was designed to remove.