A GST invoice is only valid if it contains all mandatory fields prescribed by CGST Rule 46. Missing even one field — say, the place of supply or GSTIN — makes it non-compliant. Your buyer cannot claim Input Tax Credit (ITC) on a non-compliant invoice. Here is a definitive checklist of every required field.
By Arjun Sharma· GST & Tax Compliance Specialist···Reviewed for GST accuracy
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Quick Answer
Under CGST Rule 46, every GST tax invoice must include 16 mandatory fields: supplier name, address and GSTIN; invoice serial number and date; recipient details and GSTIN (for B2B); place of supply; HSN/SAC code; item description and quantity; taxable value; GST rate; CGST/SGST or IGST amount; and the total amount payable. Missing even one of these fields makes the invoice non-compliant and your buyer cannot claim ITC.
Why Mandatory Fields Matter
Under the GST framework, the buyer's ITC claim is linked to the seller's invoice data uploaded to GSTN via GSTR-1. Rule 46 of the CGST Rules, 2017 prescribes every mandatory field. If the invoice is missing any of these fields, the tax authority can reject the ITC claim during audit. Both parties face loss: the buyer loses the tax credit, and the seller faces compliance risk.
The 16 Mandatory Fields (CGST Rule 46)
These fields must appear on every tax invoice issued by a GST-registered supplier:
#
Field Name
Notes
1
Supplier name
Legal name as registered with GSTN
2
Supplier address
Principal place of business
3
Supplier GSTIN
15-digit PAN-based number
4
Invoice serial number
Consecutive, unique within financial year
5
Date of invoice
Date of issue, not delivery date
6
Recipient name
For B2B; optional for B2C under ₹2.5 lakh
7
Recipient address
For B2B invoices
8
Recipient GSTIN/UIN
Mandatory for B2B; blank for B2C
9
Place of supply
State name + 2-digit state code
10
HSN/SAC code
HSN for goods, SAC for services
11
Description of goods/services
Must clearly identify what is being supplied
12
Quantity and unit
For goods only; not required for services
13
Taxable value
Value before tax (after discount)
14
GST rate
CGST, SGST, IGST rates shown separately
15
GST amount
CGST, SGST, IGST amounts shown separately
16
Supplier signature
Physical or digital, or authorised rep signature
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For B2C (Business to Consumer) invoices, several buyer-side fields are optional or simplified:
Field
B2B Invoice
B2C Invoice (<₹2.5L)
B2C Invoice (>₹2.5L)
Buyer GSTIN
Mandatory
Not required
Not required
Buyer name
Mandatory
Optional
Mandatory
Buyer address
Mandatory
Optional
Mandatory
Place of supply
Mandatory
Mandatory
Mandatory
IGST breakup
Mandatory if interstate
Mandatory if interstate
Mandatory if interstate
HSN Code Requirements by Turnover
HSN codes became mandatory for all GST taxpayers from April 2021. The number of digits required depends on your annual turnover:
Annual Turnover
HSN Digits Required
Up to ₹5 crore
4 digits
Above ₹5 crore
6 digits
Export invoices (any turnover)
8 digits
Important
For services, use SAC (Service Accounting Code) instead of HSN. All SAC codes are 6 digits. SAC codes start with "99".
Place of Supply — The Most Misunderstood Field
Place of supply determines whether CGST+SGST or IGST is applied. It is NOT the same as delivery address. For most services, place of supply is the recipient's state. For goods, it is where goods are delivered.
Example
A Delhi-based consultant provides legal services to a Mumbai company. Delivery address: Mumbai. Place of supply: Maharashtra (recipient's state). Tax: IGST (interstate), not CGST+SGST. If the same consultant works for a Delhi client: Place of supply = Delhi (intrastate), Tax: CGST + SGST.
Invoice Serial Number Rules
The invoice number must be unique within a financial year (April to March) and follow a consecutive series. You can use a combination of alphanumeric characters, "/" and "-" only.
Restart the series at the beginning of each financial year
You can maintain multiple series (e.g., separate series for B2B and B2C)
Cancelled invoices cannot be reused — skip the number
Maximum 16 characters allowed
Common Non-Compliance Mistakes
These are the most frequent fields suppliers get wrong or omit:
Missing place of supply — leading to wrong tax type (CGST/SGST vs IGST)
Wrong HSN code or using 4-digit HSN when 6-digit is required
No signature or stamp on physical invoices
Buyer GSTIN absent on B2B invoices
Tax amounts not shown separately (e.g., writing "18% GST: ₹5,400" instead of CGST and SGST separately)
Duplicate invoice numbers across financial years
FAQs
Is GSTIN of the buyer mandatory on all invoices?
No. Buyer GSTIN is mandatory only for B2B invoices. For B2C invoices (supply to end consumers), it is not required. However, for B2C invoices above ₹2.5 lakh for interstate supply, buyer name and address are required.
What is UIN on a GST invoice?
UIN (Unique Identification Number) is issued to certain specified entities like foreign embassies, UN bodies, and government entities that are not registered under GST but are entitled to a refund of GST paid. Such buyers provide their UIN instead of GSTIN.
Is a digital signature valid on a GST invoice?
Yes. CGST Rule 46 allows an authorised digital signature as an alternative to a physical signature. Many GST billing software tools support this.
Can I issue a GST invoice in a language other than English?
Yes. A GST invoice can be issued in any scheduled Indian language, but a translation in English or Hindi must be available on request.
What if I discover a mistake after issuing an invoice?
Issue a credit note (for downward revision) or debit note (for upward revision). Under GST, you cannot simply cancel and re-issue — the credit/debit note is the proper mechanism.
Why Businesses Stop Using Excel for GST Invoices
Manual GST calculation mistakes
One wrong CGST/SGST split or a misapplied rate triggers notices and ITC denial for your buyer.
Slow invoice creation
Copying last month's Excel file, updating dates, recalculating — 20 minutes for what should take 30 seconds.
Formatting breaks on every device
Excel invoices look different on every printer and PDF converter. Clients complain about unreadable layouts.
No easy sharing or payment link
Sending PDFs over WhatsApp with no way for clients to pay directly slows down collections.
Incorrect tax type (IGST vs CGST+SGST)
Excel can't auto-detect intra vs inter-state supply. Wrong tax type = ITC rejected for your buyer.
Disclaimer: The information in this article is for general informational purposes only and does not constitute professional tax, legal, or financial advice. GST rules and rates are subject to change. Consult a qualified CA or tax professional before making compliance decisions.
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