What makes an invoice a “GST invoice”?
A regular invoice becomes a GST tax invoice when a GST-registered business issues it for a taxable supply and includes the fields required under India’s CGST Rules. Get these fields right and your client can claim input tax credit; get them wrong and the invoice may be rejected.
Only GST-registered businesses (with a GSTIN) issue tax invoices. If you’re not registered, you issue a plain invoice or a bill of supply with no GST charged.
Mandatory fields on a GST invoice
Supplier details + GSTIN
Your legal business name, address, and 15-digit GSTIN.
Recipient details + GSTIN
The buyer's name, address, and GSTIN (for B2B). For B2C above ₹50,000, the address and state are required.
Invoice number + date
A unique, consecutive serial number (max 16 characters) and the date of issue.
HSN / SAC + description
HSN code for goods or SAC code for services, with a description, quantity, and unit.
Taxable value + rate
Value after discounts, the GST rate applied, and the tax amount.
CGST/SGST or IGST split
The correct tax heads based on place of supply, plus the total payable.
CGST + SGST vs IGST: getting the split right
The single most common GST invoice mistake is charging the wrong tax heads. The rule is simple — it depends on place of supply:
Same state → CGST + SGST
If supplier and buyer are in the same state, split the GST equally: half to CGST (central), half to SGST (state). 18% becomes 9% + 9%.
Different states → IGST
If the buyer is in another state, charge the full rate as a single IGST. 18% stays 18% IGST.
Same total either way
The buyer pays the same total. Only the distribution between central and state changes.
Not sure of the split on a given amount? The GST Calculator shows the exact CGST, SGST, and IGST breakdown instantly. The Invoice Generator applies it automatically once you pick “same state” or “other state”.
Example: an 18% GST invoice
| Field | Intra-state | Inter-state |
|---|---|---|
| Taxable value | ₹10,000 | ₹10,000 |
| CGST (9%) | ₹900 | — |
| SGST (9%) | ₹900 | — |
| IGST (18%) | — | ₹1,800 |
| Total | ₹11,800 | ₹11,800 |
Compliance tips
Keep numbers consecutive. GST requires invoice numbers in an unbroken series for each financial year. Gaps invite questions during audits.
Match the GSTIN to the state. The first two digits of a GSTIN are the state code — they should match the place-of-supply logic you used for the CGST/SGST/IGST split.
Round consistently. Tax amounts are usually rounded to two decimals (paise). A good tool handles the rounding so your CGST and SGST always sum exactly to the total GST.
This guide explains the standard format for everyday invoicing. For your specific filing obligations — thresholds, e-invoicing, and reverse charge — confirm with a qualified chartered accountant.
Related tools
- Invoice Generator — generate a GST-ready PDF invoice with the correct tax split
- GST Calculator — verify CGST/SGST/IGST on any amount
- How to create a professional invoice — the full step-by-step guide