GST Invoice Format — Mandatory Fields & Rules 2026

Updated: 3 June 2026 | CGST Rules, 2017 | E-invoicing threshold ₹5Cr

A GST tax invoice must contain: supplier's GSTIN, legal name, address, invoice number and date, buyer's name and GSTIN (B2B), HSN/SAC code, item description, quantity, taxable value, applicable GST rate, CGST/SGST/IGST amount separately, and place of supply. Serial number must be unique within a financial year.

₹5 Cr

E-invoicing threshold (mandatory)
E-invoicing is mandatory for taxpayers with annual aggregate turnover above ₹5 crore. Auto-generates IRN (Invoice Reference Number) on the IRP portal. QR code mandatory on every e-invoice.

16 Mandatory Fields on a GST Invoice

#	Field	Details
1	Name, address & GSTIN of supplier	Supplier's registered details as per GST portal
2	Consecutive serial number	Unique within financial year — letters, numbers, special chars allowed
3	Date of issue	Date of invoice issuance
4	Name, address & GSTIN of recipient	For B2B — mandatory; for B2C — GSTIN optional
5	Place of supply	State/UT code where supply takes place (determines CGST+SGST or IGST)
6	HSN / SAC code	4-digit (₹1.5–5Cr turnover) or 6-digit (₹5Cr+); SAC for services
7	Description of goods/services	Clear description of what is being supplied
8	Quantity and unit	For goods — quantity and unit of measurement (pcs, kg, mtrs, etc.)
9	Total value of supply	Gross value before discount
10	Taxable value	Value after discount — GST is calculated on this
11	Rate and amount of tax	CGST / SGST / IGST / UTGST — shown separately
12	Total tax charged	Sum of all tax components
13	Amount of reverse charge	If applicable — for RCM (Reverse Charge Mechanism) supplies
14	Signature or digital signature	Of authorized signatory or their representative
15	Name of state and code	Both supplier and recipient state name and code
16	Address of delivery	If different from the billing address of recipient

B2B vs B2C Invoice — Key Differences

B2B Invoice (Registered Buyer)

Buyer's GSTIN is mandatory
Full tax invoice required in all cases
Reported in GSTR-1 B2B table
Buyer can claim Input Tax Credit (ITC)
No threshold for reporting

B2C Invoice (Unregistered Buyer)

Recipient GSTIN not required
B2C Large: interstate + value > ₹2.5L — must be reported in GSTR-1
B2C Small: consolidated summary in GSTR-1
No ITC available to buyer
QR code on invoice if B2C e-invoice applicable

E-Invoicing — How It Works

Who must use it: Taxpayers with annual aggregate turnover above ₹5 crore (all sectors except specified exemptions).

Process: Generate invoice in your billing software → Upload to Invoice Registration Portal (IRP: einvoice1.gst.gov.in) → IRP validates and returns IRN + QR code → Auto-populates GSTR-1 and e-way bill data.

IRN: 64-character unique hash. Must be printed/displayed on every e-invoice.

QR Code: Mandatory on e-invoices. Contains key invoice details for verification.

Debit Note vs Credit Note Under GST

Type	When Issued	Effect	Reference Required
Debit Note	Increase in taxable value (under-billed)	Increases supplier's tax liability	Original invoice number and date
Credit Note	Decrease in value (over-billed / goods returned)	Reduces supplier's tax liability	Original invoice number and date

Both debit and credit notes must reference the original invoice number and date. Credit notes must be issued by 30 September of the following financial year, or before the annual return filing date — whichever is earlier.

Frequently Asked Questions

Can I use any format for a GST invoice?

There is no prescribed format, but all 16+ mandatory fields must be present. You can use Excel, Tally, accounting software, or GST billing apps — as long as all required fields are included. The format is flexible but the content requirements are strict under the CGST Rules.

Is e-invoicing mandatory for all businesses?

E-invoicing is mandatory for businesses with aggregate annual turnover above ₹5 crore. Businesses below ₹5 crore can voluntarily use e-invoicing. Check cbic.gov.in for the latest threshold notifications, as the government has progressively reduced the threshold over the years.

What is an IRN in GST e-invoicing?

IRN (Invoice Reference Number) is a unique 64-character alphanumeric hash generated by the Invoice Registration Portal (IRP) for each e-invoice. It is generated using the GSTIN of supplier, document type, financial year, and invoice number. The IRN must be printed or displayed on the physical invoice along with a QR code.

How many copies of a GST invoice are required?

For goods: 3 copies — original for buyer, duplicate for transporter, and triplicate for supplier. For services: 2 copies — original for recipient and duplicate for supplier. Under e-invoicing, the IRP-generated document serves as the reference but physical copies may still be needed for transport.

What is the time limit to issue a GST invoice?

For goods: at or before the time of delivery or removal of goods. For services: within 30 days of the date of supply (45 days for banking companies and NBFCs). For continuous supply services (telecom, utilities): invoice must be issued at each due date or statement date as per the contract.

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