GST Invoice Format: Mandatory Fields Under Rule 46

Short answer: A Goods and Services Tax (GST) invoice is a legal document that must contain specific information as prescribed under Rule 46 of the CGST Rules, 2017. Key mandatory fields include the supplier's and recipient's name, address, and GSTIN, a consecutive serial number, date of issue, HSN codes for goods/services, taxable value, tax rate, and amount. A compliant invoice is essential for the recipient to claim Input Tax Credit (ITC).

What are the mandatory fields for a GST tax invoice?

A proper tax invoice is the foundation of the GST system, as it provides evidence of a transaction and is a crucial document for claiming ITC. Rule 46 of the Central Goods and Services Tax (CGST) Rules, 2017, specifies all the details that a tax invoice must contain. Failing to include any of these can lead to penalties and disputes with the tax authorities, and may cause your customers to lose their ITC.

Here is a checklist of the mandatory fields for a tax invoice:

Field Name	Description	Importance
Supplier Details	Name, address, and GST Identification Number (GSTIN) of the supplier.	Identifies the seller for tax purposes.
Invoice Number	A consecutive serial number, unique for the financial year. It can contain alphabets, numerals, and special characters like a hyphen or slash.	Ensures proper tracking and audit trail.
Date of Issue	The date on which the invoice is created.	Determines the tax period for reporting in GSTR-1.
Recipient Details	Name, address, and GSTIN of the recipient (if registered).	Crucial for the buyer to claim Input Tax Credit.
Shipping & Billing Address	If the delivery address is different from the billing address, both must be mentioned.	Determines the Place of Supply.
HSN/SAC Code	Harmonized System of Nomenclature (for goods) or Service Accounting Code (for services).	Classifies goods and services for tax rate determination.
Description of Goods/Services	A clear description of the items being sold, including quantity and unit (e.g., kgs, pcs, ltrs).	Details the nature of the transaction.
Taxable Value	The value of goods or services after deducting any discounts but before adding GST.	The base amount on which tax is calculated.
Tax Rate & Amount	The applicable rates and amounts of CGST, SGST, UTGST, IGST, and Cess, shown separately.	Ensures correct tax calculation and payment.
Total Value	The total amount payable, including the taxable value and all taxes.	The final amount the customer must pay.
Place of Supply	The state where the goods or services are considered to be supplied.	Determines whether CGST+SGST/UTGST or IGST is applicable.
Signature	Signature or Digital Signature of the supplier or their authorized representative.	Authenticates the document.
QR Code	For B2C invoices issued by taxpayers with an aggregate turnover exceeding a prescribed limit, a dynamic QR code is required.	Facilitates digital payments.

Is HSN/SAC code mandatory on every invoice?

Yes, mentioning the HSN (Harmonized System of Nomenclature) for goods or SAC (Service Accounting Code) for services is mandatory for all GST-registered taxpayers. The number of digits required depends on your aggregate annual turnover in the preceding financial year.

• Turnover up to ₹5 crores: B2B invoices must have a minimum of 4-digit HSN codes. It is optional for B2C invoices.
• Turnover above ₹5 crores: A 6-digit HSN code is mandatory for all invoices, both B2B and B2C.

Using the correct HSN code is critical, as it determines the applicable GST rate. You can find the right codes on the GST portal or consult a tax professional. For more information, refer to our HSN code search guide.

What is the difference between a tax invoice and a bill of supply?

A tax invoice and a bill of supply are both commercial instruments, but they serve different purposes under GST.

• Tax Invoice: Issued by a regular registered taxpayer for taxable supplies. It contains a detailed tax breakdown (CGST, SGST, IGST) and is the primary document for the recipient to claim ITC.

• Bill of Supply: Issued in two specific cases:

  1. By a registered person supplying exempted goods or services.
  2. By a registered person enrolled under the composition scheme.

A bill of supply does not show any tax amount because the supplier cannot charge tax from the customer. Consequently, the buyer cannot claim any ITC on the basis of a bill of supply.

Do I need a unique invoice number for every bill?

Yes, the invoice numbering system must be strictly followed as per Rule 46. Every tax invoice must have a consecutive serial number that is unique for each financial year. This series must not be broken or reset during the financial year. You can, however, maintain multiple invoice series for different branches or types of supplies, as long as each series is unique and consecutive.

For example, a valid series could be SPSC/2026-27/001, SPSC/2026-27/002, and so on. A new series must start from 1st April of the next financial year.

What are the requirements for e-invoicing?

E-invoicing is a system where B2B invoices are electronically authenticated by the GST Network (GSTN) for further use on the common GST portal. It is mandatory for registered persons whose aggregate turnover in any preceding financial year from 2017-18 onwards exceeds a certain threshold (currently ₹5 crores).

Under this system, the seller first prepares a standard invoice using their accounting software. This invoice data (in JSON format) is then uploaded to the Invoice Registration Portal (IRP). The IRP validates the data, generates a unique Invoice Reference Number (IRN) and a digitally signed QR code, and sends it back to the seller. The invoice with the embedded IRN and QR code is the valid e-invoice. Explore more at our guide on e-invoicing under GST.

When must a tax invoice be issued?

The timing for issuing a GST invoice is defined by the time of supply rules under the CGST Act.

• For Supply of Goods: The invoice must be issued on or before the date of removal or delivery of the goods.
• For Supply of Services: The invoice must be issued within 30 days from the date of supply of the service (45 days in case of banks and financial institutions).

Timely issuance is crucial as it determines the month in which the tax liability needs to be reported and paid.

Worked example

Let's consider a transaction in Bengaluru, Karnataka.

• Supplier: 'Bengaluru Tech Solutions Pvt. Ltd.', located in Bengaluru, Karnataka (GSTIN: 29ABCDE1234F1Z5).
• Recipient: 'Chennai Client Corp.', located in Chennai, Tamil Nadu (GSTIN: 33FGHIJ5678K2Z9).
• Transaction: Sale of 5 units of 'High-Performance Servers'.

Invoice Calculation:

1. Product: High-Performance Server
2. HSN Code (8 digits): 8471 50 00
3. Quantity: 5 units
4. Price per unit: ₹1,50,000
5. Total Basic Value: 5 x ₹1,50,000 = ₹7,50,000
6. Discount @ 2%: ₹15,000
7. Taxable Value: ₹7,50,000 - ₹15,000 = ₹7,35,000
8. Place of Supply: Tamil Nadu (since goods are delivered to Chennai)
9. Applicable Tax: This is an inter-state supply, so IGST applies.
10. GST Rate (assumed): 18% IGST
11. IGST Amount: 18% of ₹7,35,000 = ₹1,32,300
12. Total Invoice Value: ₹7,35,000 (Taxable Value) + ₹1,32,300 (IGST) = ₹8,67,300

The final invoice issued by Bengaluru Tech Solutions would clearly show all these details, including both parties' GSTINs, the HSN code, taxable value, IGST rate and amount, and the total value. The invoice serial number would be unique, for example, BTS/2627/INV-045.

Common mistakes

1. Missing or Incorrect Buyer's GSTIN: This is a major error that will directly lead to the denial of ITC for your customer.
2. Incorrect Place of Supply: Applying CGST+SGST on an inter-state supply or IGST on an intra-state supply is a common but serious compliance error.
3. Not Following Serial Number Rules: Using duplicate invoice numbers or breaking the consecutive sequence can attract scrutiny from tax officials.
4. Omitting HSN/SAC Codes: Failing to mention the HSN/SAC code or using an incorrect number of digits as per turnover can lead to penalties.
5. Mathematical Errors: Simple errors in calculating taxable value or tax amounts can lead to incorrect GST payments and require issuing debit or credit notes.
6. Issuing Invoices Late: Not adhering to the time of supply rules for issuing invoices can result in interest and penalties.

How SP & SC helps

Ensuring every invoice is 100% compliant can be a daunting task for a growing business. At SP & SC, we help you streamline this process. Our team of Chartered Accountants and tax experts will review your current invoicing practices, help configure your accounting software for accurate invoice generation, and ensure that all data flows correctly into your monthly and quarterly GST returns. We manage the entire lifecycle from invoice validation to GST return filing, helping you avoid costly mistakes and remain fully compliant. We also assist in responding to any departmental queries related to invoicing discrepancies.

Frequently asked questions

Q1. Can I issue a handwritten GST invoice?

Yes, a handwritten invoice is legally valid provided it contains all the mandatory fields prescribed under Rule 46. However, it must be legible and preferably prepared in triplicate (for goods) or duplicate (for services). For businesses subject to e-invoicing, a handwritten invoice is not a substitute for generating an IRN.

Q2. What happens if I make a mistake on a GST invoice?

You cannot simply edit or cancel an already issued GST invoice. If you have charged a lower value or tax, you must issue a Debit Note. If you have overcharged, you must issue a Credit Note. These documents must also be serially numbered and reported in your GSTR-1.

Q3. How long should I keep records of my GST invoices?

As per Section 36 of the CGST Act, you must retain all books of accounts, including sales and purchase invoices, for a period of 72 months (6 years) from the due date of filing the annual return for the relevant year.

Q4. Is an invoice with a QR code mandatory?

A dynamic QR code is mandatory on B2C (Business to Consumer) invoices for registered persons whose aggregate turnover exceeds ₹500 crores (this threshold is subject to change). The QR code contains payment details and allows for easy payment via UPI, helping to digitize payment collections.

Get a fixed-fee quote

Stop worrying about GST compliance. Share your documents with us for a thorough review and receive a written fixed-fee quote for our end-to-end compliance services. Contact SP & SC via our website, or WhatsApp us at +91 90356 74566. We handle all GST, income tax, and corporate law matters, allowing you to focus on your business.