10 Things Your GST Invoice Must Have as per CGST Rules
GST invoices must follow Rule 46 of the CGST Rules, 2017, which specifies 16 mandatory fields. Missing or incorrect details can invalidate the invoice, block the buyer’s ITC claim, and lead to penalties. Here’s a practical guide to every required field and common errors.
A GST invoice is a legal document. It is not just a payment request. Rule 46 of the CGST Rules, 2017 prescribes 16 mandatory fields every tax invoice must contain. Miss even one and the invoice can be treated as invalid. Your buyer cannot claim input tax credit on it. You may face a penalty of up to INR 25,000 per incorrect invoice under Section 122 of the CGST Act.
The ten points below cover every field that matters in practice, with the errors that most commonly occur against each one.
What Must a GST Invoice Contain Under Rule 46?
A valid GST tax invoice must have 16 mandatory fields under Rule 46 of the CGST Rules: the heading "Tax Invoice," supplier name, GSTIN, and address, a unique sequential invoice number up to 16 characters, date, buyer details and GSTIN, place of supply, HSN or SAC code, description, quantity, taxable value, GST rate, tax breakup by CGST and SGST or IGST, and a signature. Missing any one can make the invoice invalid for ITC.
1. The Words "Tax Invoice" at the Top
The document must say "Tax Invoice" on it. Not "Invoice." Not "Bill." Not "Receipt." Not "Tax Bill."
This is required explicitly under Rule 46(a). An invoice without the correct heading can be refused for ITC by the buyer's accounts team. Proforma invoices, receipts, and quotations look similar but are different documents. The heading is what separates a legally valid GST invoice from a commercial document.
Muskaan Kapoor
2. Your Name, Address, and GSTIN
Your name on the invoice must match the legal name on your GST registration exactly, not a trade name or abbreviation. If your company is registered as "Sharma Enterprises Private Limited," writing "Sharma Enterprises" or "Sharma Pvt Ltd" is not sufficient.
Your GSTIN is a 15-character alphanumeric code. Without it, the invoice is not a valid GST document. Your buyer cannot claim ITC on an invoice without the supplier's GSTIN.
Your registered address must also appear. This does not have to be the address where the goods were dispatched from, but it must be your GST registration address.
3. A Unique, Sequential Invoice Number
The invoice number must be unique within the financial year, sequential with no gaps, a maximum of 16 characters, and contain only letters (A-Z), numbers (0-9), hyphens (-), or slashes (/).
You cannot reuse an invoice number. You cannot skip numbers. You cannot have two invoices with the same number in the same financial year.
Acceptable formats: INV/2026-27/001, RS-2627-0001, 2026-001.
Businesses with multiple branches can maintain separate number series per branch, for example KAR-001 for Karnataka and MUM-001 for Mumbai, as long as each series is sequential within itself.
Invoice numbers reset at the start of each financial year (April 1). Using last year's numbering sequence into the new year is a mistake that causes GSTR-1 filing errors.
4. Date of Issue
The invoice date must appear on every invoice. This determines the tax period in which the supply is reported and the deadline for the buyer to claim ITC.
For goods: The invoice must be issued at or before the time of removal or delivery of goods.
For services: The invoice must be issued within 30 days of the date of supply. For banking, insurance, and financial services, the window is 45 days.
Backdating invoices or issuing invoices significantly after the service is delivered is a compliance error. It mismatches the reporting period in GSTR-1 with the actual supply period.
5. Buyer's Name, Address, and GSTIN
For B2B transactions, the buyer's full legal name, registered address, and GSTIN must appear on the invoice. The buyer uses this to claim ITC in their GSTR-3B. A wrong GSTIN means the invoice will not appear in the buyer's GSTR-2B. They cannot claim ITC. They will ask you to issue a corrected invoice.
For B2C transactions to unregistered buyers, you do not need the GSTIN. But if the invoice value exceeds INR 50,000, you must still capture the buyer's name, address, and state.
Before entering any buyer's GSTIN on an invoice, verify it on the GST portal at gst.gov.in. A GSTIN that looks valid may have been suspended or cancelled. Invoicing to a cancelled GSTIN creates reconciliation problems later.
Muskaan Kapoor
6. Place of Supply
The place of supply determines whether you charge CGST and SGST or IGST.
Same state as your registration: CGST (9%) plus SGST (9%). Different state from your registration: IGST (18%).
For goods, the place of supply is generally where the goods are delivered. For most B2B services, it is the registered address of the recipient.
Getting the place of supply wrong is one of the most common causes of ITC rejection. A buyer in Delhi cannot claim ITC on CGST and SGST charged by a supplier in Mumbai. The wrong tax type on the invoice makes the ITC ineligible entirely.
The state name and code must appear on the invoice. The first two digits of a GSTIN are the state code. If the buyer's state code differs from yours, charge IGST.
7. HSN Code (for Goods) or SAC Code (for Services)
HSN codes classify goods. SAC codes classify services. Both are mandatory on GST invoices. The number of digits required depends on your annual turnover:
Using the wrong number of digits does not make the invoice invalid on its face, but it causes errors in the HSN summary (Table 12 of GSTR-1). Table 12 is mandatory above INR 1.5 crore in annual turnover. Portal validation errors in Table 12 can block GSTR-1 submission.
Wrong HSN codes also suggest that the incorrect tax rate may have been applied, which opens up the invoice to reassessment during audits.
8. Description of Goods or Services
The invoice must describe what was supplied. The description does not need to be elaborate but must be clear enough to identify the goods or services. "Professional services" is not sufficient. "Social media marketing services for the period June 2026" is.
Vague descriptions are an audit risk. They suggest the supply type is unclear, which makes it harder to verify the correct GST rate was applied.
9. Taxable Value and GST Breakup
The invoice must show:
- The value of goods or services before GST (taxable value)
- The GST rate applied
- The GST amount split by type: CGST and SGST separately for intra-state, IGST for inter-state
You cannot show a single lump sum. The tax breakup must be explicit. For example:
Taxable value: INR 1,00,000 CGST at 9%: INR 9,000 SGST at 9%: INR 9,000 Total: INR 1,18,000
If there are multiple items at different tax rates, each rate and its corresponding tax amount must be shown separately. The buyer's accounts team will reject any invoice where they cannot verify the tax calculation.
10. Signature or Digital Signature
Rule 46 requires the invoice to be signed or digitally signed by the supplier or an authorised representative. For invoices generated digitally and shared as PDFs, a digital signature or a stamp and signature of the authorised person is required.
One important exception: if you generate an e-invoice and obtain an IRN from the Invoice Registration Portal, the IRN and QR code on the invoice satisfy the authentication requirement. A separate signature is not required on e-invoices that carry a valid IRN.
For businesses above INR 5 crore annual turnover where e-invoicing is mandatory, every B2B invoice must carry the IRN and a digitally signed QR code from the IRP. An invoice without the IRN is treated as legally invalid under Rule 48(4) of the CGST Rules.
Additional Field for B2C Invoices Above INR 50,000
For invoices to unregistered buyers where the invoice value exceeds INR 50,000, you must also capture the buyer's name, address, and the state of delivery. This is required under Rule 46(b) and is specifically to capture inter-state B2C supplies correctly in GSTR-1.
What Happens When a Mandatory Field Is Missing
The consequences depend on which field is missing and whether the buyer catches it before or after claiming ITC.
If the buyer claims ITC on an invalid invoice and the error is found during audit, the ITC is reversed and interest at 18% per year applies from the date it was claimed. The buyer then comes back to the supplier to issue a corrected invoice.
If the missing field is the supplier's GSTIN, the invoice is not a valid GST document at all. No ITC claim is possible, and the supply may be treated as unregistered for that period.
A penalty of up to INR 25,000 per incorrect invoice applies under Section 122 for non-compliant invoice issuance.
How BillForge Handles This
Every invoice created in GST invoicing software that validates against Rule 46 is checked before it can be saved. The GSTIN field verifies against the GST portal. The invoice number follows a sequential, non-repeating series automatically. The place of supply is determined from the buyer's GSTIN state code. HSN and SAC codes are validated against the GST rate schedule. If a mandatory field is missing or incorrect, the invoice does not save until it is fixed. For businesses that have also crossed the e-invoice limit, see the full guide on GST e-invoice requirements.
Muskaan Kapoor
FAQs
What are the mandatory fields on a GST invoice as per Rule 46?
Rule 46 of the CGST Rules requires 16 mandatory fields: the heading "Tax Invoice," supplier name, GSTIN, and address, a unique sequential invoice number (max 16 characters), date of issue, buyer name, address, and GSTIN, place of supply, HSN or SAC code, description of goods or services, quantity, taxable value, GST rate, tax amount split by type (CGST/SGST or IGST), and a signature or digital signature.
What is the penalty for a wrong or incomplete GST invoice?
A penalty of up to INR 25,000 per incorrect invoice under Section 122 of the CGST Act. The buyer also loses their ITC claim on the invoice if mandatory fields are missing or incorrect.
How many digits of HSN code are required on a GST invoice?
It depends on your annual turnover. 2 digits for INR 1.5 crore to INR 5 crore. 4 digits for INR 5 crore to INR 10 crore. 6 digits for above INR 10 crore. Businesses under INR 1.5 crore are not required to include HSN codes but it is recommended.
Is a digital signature required on every GST invoice?
A signature is required under Rule 46. However, for e-invoices where an IRN has been obtained from the Invoice Registration Portal, the IRN and QR code satisfy the authentication requirement. A separate signature is not needed on IRN-validated invoices.
Can I send a GST invoice by email or WhatsApp?
Yes. A soft-copy PDF shared by email or WhatsApp is acceptable as long as all mandatory fields are present. For businesses above INR 5 crore turnover where e-invoicing is mandatory, the invoice must carry the IRN and QR code from the IRP before being shared.
