What a valid GST tax invoice must show: Rule 46 fields, the 16-character serial number and HSN digits

Last updated 22 Oct 2026 · India

Short answer. Under Rule 46 of the CGST Rules a tax invoice must show the supplier's name, address and GSTIN, a consecutive serial number of up to 16 characters (letters, numbers, '-' and '/') that is unique for the financial year, the date, the recipient's name, address and GSTIN (if registered), HSN/SAC, description, quantity, taxable value, rate and amount of tax, place of supply for inter-state supplies, whether tax is payable on reverse charge, and a signature or digital signature. For services, issue it within 30 days of supply (Rule 47).

Field checklist

Field	Note
Supplier name, address, GSTIN	As on the registration certificate
Invoice number	Max 16 characters; one or more series; unique per FY
Recipient details	GSTIN if registered; for unregistered recipients with value ₹50,000 or more, name, address and state
HSN / SAC	4 digits up to ₹5 crore turnover, 6 digits above (Notification 78/2020-CT)
Values and tax	Taxable value after discount, rate and amount of CGST/SGST/IGST
Place of supply	With state name, for inter-state supplies
Reverse charge	State whether tax is payable on reverse charge
Signature	Signature or digital signature of the supplier or authorised person

Copies (Rule 48)

Goods: original for recipient, duplicate for transporter, triplicate for supplier. Services: original and duplicate. Businesses covered by e-invoicing must also report to the IRP.

Common mistakes

Restarting numbering mid-year or reusing a number across branches on one GSTIN.
Long invoice numbers over 16 characters (e.g. full dates plus branch codes).
No place of supply on inter-state invoices, leading to wrong IGST/CGST split.
Missing reverse-charge flag.

Frequently asked questions

How long can a GST invoice number be?

Up to 16 characters, using letters, numbers, hyphen or slash, unique for the financial year (Rule 46(b)).

Is HSN code mandatory on a GST invoice?

Yes: 4 digits for turnover up to ₹5 crore and 6 digits above, as notified in Notification 78/2020-Central Tax.

What is the time limit to issue an invoice for services?

Within 30 days of the date of supply of service (Rule 47).

How many copies of a GST invoice are needed for goods?

Three: original for the recipient, duplicate for the transporter and triplicate for the supplier (Rule 48).

Official sources

Not tax or legal advice. This is a free explainer of public rules; deadlines and rules can change by notification, so confirm on the official portal or with your CA before you file. Last checked 22 Oct 2026.

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