Context
GST does not use one universal document — which one a supplier issues depends on their registration status and the nature of the supply. The decision tree above resolves the choice between a tax invoice, a bill of supply, and the informal kaccha bill, starting from a single question: is the supplier GST-registered?
The first branch is registered + regular scheme + taxable supply. Here Section 31 of the CGST Act[1] requires a tax invoice carrying the full Rule 46 particulars — the supplier charges GST, shows the CGST/SGST or IGST split, and the buyer can claim input tax credit. This is the document most B2B transactions run on. The second branch covers a registered supplier who is either under the composition scheme or supplying exempt or nil-rated goods. Such a supplier cannot collect GST, so Section 31(3)(c) and Rule 49[1][2] direct them to issue a bill of supply instead — same commercial detail, but no tax line and no ITC for the buyer.
The third branch is the unregistered supplier below the registration threshold. Without a GSTIN there is no GST to charge, so the supplier issues a plain invoice or bill of supply with no tax component. This is legitimate — being below the threshold is not the same as being non-compliant. The kaccha bill sits outside all three branches: it is an informal slip with no GSTIN, no tax split, and no return trail, and the GST law does not recognise it as any kind of statutory document. Issuing a kaccha bill where a tax invoice is required is a breach; relying on one as a buyer forfeits ITC.
The trap most businesses fall into is treating "bill of supply" and "kaccha bill" as the same thing because neither shows GST. They are not. A bill of supply is a proper GST document issued by a registered composition or exempt-goods supplier, with its own format under Rule 49; a kaccha bill is the absence of any GST document. The registration status of the supplier — not the look of the paper — is what decides which branch you are on.