GST Invoice Format: Mandatory Fields Checklist

A correct GST invoice format is the foundation of every other GST compliance task. Your invoice is the document your customer relies on to claim input tax credit, the record that feeds your GSTR-1 and e-invoice data, and the first thing an officer examines in an audit. Rule 46 of the CGST Rules lists the fields a tax invoice must contain. Missing even one, such as place of supply or the reverse charge declaration, can lead to disputes over credit. This checklist explains each mandatory field, the variations for B2C, exports and composition dealers, and the timing and numbering rules that billing teams often miss.

Tax invoice versus other GST documents

GST recognises several documents, and using the wrong one is a common error.

Document	When it is used
Tax invoice	Taxable supplies by a registered person
Bill of supply	Exempt supplies, and all supplies by composition taxpayers
Revised invoice	Supplies made between the effective date of registration and the date the registration certificate was issued
Credit note / debit note	Reduction or increase in value or tax after an invoice was issued
Receipt voucher	Advance received for a supply
Refund voucher	Advance refunded when no supply is made
Payment voucher and self-invoice	Purchases under reverse charge, especially from unregistered suppliers
Delivery challan	Movement of goods without a sale, such as job work or supply on approval

Mandatory fields on a GST tax invoice

Under rule 46, a tax invoice must contain the following particulars:

1. Name, address and GSTIN of the supplier.
2. Invoice number: a consecutive serial number of up to 16 characters, in one or more series, unique for the financial year. It may contain letters, numbers, hyphen and slash.
3. Date of issue.
4. Name, address and GSTIN or UIN of the recipient, if registered.
5. For unregistered recipients where the taxable value is ₹50,000 or more: name and address of the recipient, address of delivery, and the name and code of the state.
6. HSN code for goods or SAC code for services, at the number of digits prescribed for your turnover.
7. Description of goods or services.
8. Quantity and unit (for goods).
9. Total value of the supply.
10. Taxable value after discounts and abatements.
11. Rate of tax: CGST, SGST or UTGST, IGST and cess where applicable.
12. Amount of tax under each head.
13. Place of supply with the name of the state, for inter-state supplies.
14. Address of delivery where it differs from the place of supply.
15. Whether tax is payable on reverse charge.
16. Signature or digital signature of the supplier or authorised representative (not required for electronically issued e-invoices authenticated through the IRP process).
17. QR code with IRN, for taxpayers covered by e-invoicing.

HSN digits by turnover

Aggregate turnover in previous year	HSN/SAC digits required
Up to ₹5 crore	4 digits on B2B invoices (optional on B2C)
Above ₹5 crore	6 digits on all invoices

Not sure about your codes? Our guide on how to find HSN and SAC codes walks through the official search tools.

A worked example of the tax block

A Bengaluru furniture maker sells 10 office chairs at ₹6,000 each to a registered company in Bengaluru and allows a trade discount of 5% on the invoice. Assume the chairs attract 18% GST (verify the current rate for your HSN).

Line	Amount
Gross value (10 x ₹6,000)	₹60,000
Less trade discount at 5%	₹3,000
Taxable value	₹57,000
CGST at 9%	₹5,130
SGST at 9%	₹5,130
Invoice total	₹67,260

Because the discount is shown on the invoice itself, it is excluded from the taxable value. Had the same company been in Chennai, the place of supply would be Tamil Nadu and the tax would be IGST of 18%, that is ₹10,260, with the same invoice total of ₹67,260.

Special cases

B2C invoices and small-value sales

For supplies to unregistered persons, a tax invoice is still required, but where the value is below ₹200 and the buyer does not ask for an invoice, a consolidated daily invoice may be issued for such sales. Very large businesses notified for dynamic QR codes on B2C invoices must print a QR code that allows digital payment.

Exports

Export invoices carry the endorsement "supply meant for export on payment of IGST" or "supply meant for export under bond or letter of undertaking without payment of IGST", along with the name and address of the recipient, address of delivery and name of the destination country.

Composition taxpayers

A composition dealer issues a bill of supply, cannot charge tax on it, and must mention "composition taxable person, not eligible to collect tax on supplies".

Reverse charge

When the supply attracts reverse charge, the supplier's invoice must clearly state that tax is payable by the recipient. If you buy from an unregistered supplier under reverse charge, you issue the self-invoice yourself.

Time limit for issuing invoices

• Goods: on or before removal of goods for supply, or delivery where no movement is involved. For continuous supplies, on or before the date of the account statement or payment.
• Services: within 30 days of the date of supply (45 days for banks, insurers and NBFCs).
• E-invoices: taxpayers with aggregate turnover of ₹10 crore and above must report invoices to the IRP within 30 days of the invoice date, otherwise the IRP rejects them.

Invoice copies

For goods, prepare the invoice in triplicate: original for the recipient, duplicate for the transporter and triplicate for the supplier. For services, prepare it in duplicate. Where an e-invoice is generated and the e-way bill is linked, the transporter can rely on the IRN instead of a physical duplicate.

Common invoicing mistakes

• Restarting or duplicating invoice numbers mid-year, or reusing a cancelled number.
• Charging CGST and SGST on inter-state supplies because the billing address was used instead of the delivery state for goods.
• Missing place of supply, which prevents buyers from validating their credit.
• Outdated tax rates after the September 2025 GST rate rationalisation, which moved most goods to 5% or 18% slabs.
• Not showing discounts on the invoice, so the discount cannot reduce taxable value.
• Using a tax invoice for exempt goods instead of a bill of supply.

Printable checklist for your billing team

1. Supplier GSTIN, name and address printed correctly.
2. Invoice number continuous, unique for the year, 16 characters or fewer.
3. Buyer GSTIN validated; state code matches.
4. Place of supply decided by the rules, not by habit.
5. HSN or SAC at the required digits.
6. Current rate applied; CGST/SGST or IGST chosen correctly.
7. Discount shown on the face of the invoice if it should reduce taxable value.
8. Reverse charge field filled (Yes or No).
9. IRN and QR code present if e-invoicing applies.
10. Signature or digital signature applied.

Cancelling and correcting invoices the right way

Invoices are not edited after issue. When something is wrong, GST provides specific routes, and choosing the right one keeps your GSTR-1 and your customer's GSTR-2B consistent.

Cancellation

If a supply did not happen at all, for example an order was cancelled before dispatch, the invoice can be cancelled. Keep the cancelled document on record with its number, so the series stays continuous, and report the cancelled count in Table 13 of GSTR-1. For e-invoices, the IRN can be cancelled on the IRP only within 24 hours of generation; after that, a credit note is needed.

Credit note

If the taxable value or tax charged was higher than it should have been, or goods were returned, issue a credit note linked to the original invoice. The time limit is 30 November following the end of the financial year or the date of filing the annual return, whichever is earlier.

Debit note

If the value or tax was understated, issue a debit note for the difference. The buyer can claim credit on it in the period it appears in GSTR-2B.

Amendment in GSTR-1

Errors in details that do not change the value, such as a wrong GSTIN or place of supply, are corrected by amending the invoice in a later GSTR-1 or in GSTR-1A, not by issuing a credit note.

The worked example in this guide also shows why discounts deserve care. If the 5% discount had been given later through a credit note instead of on the invoice, GST could be reduced only if the discount was agreed before the supply and linked to specific invoices, and the buyer reversed the matching credit.

How Fininvo helps

Fininvo ERP produces GST tax invoices with CGST, SGST and IGST calculated from the supply type, HSN and SAC codes mapped on each item, and place of supply and reverse charge handled on the document. Customisable templates cover tax invoices, proforma invoices, export invoices and delivery challans. See GST invoicing, tax compliance and pricing.

General information, not tax advice. Confirm rates and rules with the latest CBIC notifications and your CA.

Frequently Asked Questions

Is a signature mandatory on a GST invoice?

Rule 46 requires a signature or digital signature. For e-invoices authenticated through the IRP, the IRP's digital signature and the QR code serve as authentication, so a manual signature is not needed.

Can invoice numbers have letters?

Yes. Invoice numbers can contain letters, numbers, hyphens and slashes, up to 16 characters, and must be unique for the financial year. Many businesses use a branch prefix plus the year, such as BLR/26-27/0001.

Do I need the buyer's address on a B2C invoice?

For unregistered buyers, the name, address, delivery address and state are mandatory where the taxable value is ₹50,000 or more. Below that, they are not mandatory, though capturing the state helps you determine the place of supply.

What happens if I issue an invoice without HSN?

The invoice is not fully compliant, and your HSN summary in GSTR-1 will be incomplete. Officers can question it, and a penalty for incorrect documents may apply. Update the item master and issue invoices with the required digits.

Is a proforma invoice a GST document?

No. A proforma invoice is a quotation-like document and has no legal status under GST. Tax is charged only on the tax invoice issued at the time of supply.