CGST/SGST vs IGST: GST Invoicing Without the Headache
The whole of India's dual-GST split comes down to one question: is the supply inside the state or across a state line? Get that right and the rest follows.
India runs a dual GST. The same tax rate applies to a sale, but how it's split depends on geography. Get the split wrong on an invoice and your customer can't claim the right input credit, and your filings won't reconcile. The good news: the rule that drives everything is a single comparison.
Place of supply is the whole game
Compare the supplier's state to the place of supply (broadly, where the customer receives the goods or service):
- Same state (intra-state): the tax splits in half into
CGST(central) andSGST(state). An 18% rate becomes 9% CGST + 9% SGST. - Different states (inter-state): the whole tax is a single
IGST(integrated). An 18% rate is simply 18% IGST, no split.
That's it. The customer pays the same total either way; the invoice just has to label the components correctly so credits flow to the right place.
The details that trip people up
- Rounding. Compute tax per line, then decide where you round. Rounding each component independently can make CGST + SGST drift a paisa away from half the total. DocForge computes consistently and applies a single rounding adjustment so the components always sum to the tax shown.
- Discounts. A discount has to come off the taxable value before tax is computed, not after. Tax on a pre-discount amount over-charges the customer.
- Mixed rates. Different line items can carry different GST rates. Tax is a per-line calculation that you sum — never a single rate applied to the invoice total.
- The required fields. A compliant tax invoice needs your GSTIN, the customer's GSTIN where applicable, HSN/SAC codes, place of supply, and a gap-free invoice number. Missing fields are the most common reason an invoice gets rejected for input credit.
How DocForge handles it
You set the supplier state and enter the place of supply; DocForge picks CGST/SGST or IGST automatically and computes each line's tax, applies discounts to the taxable value first, and reconciles rounding so the totals are internally consistent. The invoice template already carries the required fields, and numbering is gap-free by construction. You fill in line items and a customer; the compliant tax math is done for you.
GST invoicing feels fiddly because the edge cases are where the penalties live. Encode the place-of-supply rule once and the fiddliness disappears into the engine.