If you run a business in India or work in accounts, the term "GST invoice" comes up every single day. But what exactly makes a document a legally valid GST invoice? What fields are mandatory, when must one be issued, and how is it different from a simple bill or a bill of supply? This complete guide covers everything you need to know about GST invoices in India for 2025 — whether you are a first-time freelancer or an experienced accountant refreshing your knowledge.
A GST invoice (formally called a Tax Invoice under the CGST Act, 2017) is a document issued by a GST-registered supplier to a buyer when a taxable supply of goods or services is made. It serves three key purposes: it is a request for payment, a record of the transaction, and most importantly, the document that entitles the buyer to claim Input Tax Credit (ITC). Without a valid GST invoice from the supplier, the buyer cannot legally claim ITC, making invoice accuracy critical in any B2B transaction.
A registered supplier must issue a tax invoice in the following situations:
For B2C small transactions (services to unregistered buyers below ₹2 lakh), a simplified tax invoice or receipt voucher is acceptable. For intra-state transactions, the invoice must show CGST and SGST separately. For inter-state transactions, IGST is shown instead.
Rule 46 of the CGST Rules, 2017 specifies the fields that every tax invoice must contain. Missing even one mandatory field can make the invoice invalid for ITC purposes.
| Field | Description | Mandatory? |
|---|---|---|
| Supplier's Name & Address | Legal name and registered address of the seller | Yes |
| Supplier's GSTIN | 15-digit GST Identification Number of the seller | Yes |
| Invoice Number | Unique sequential number within a financial year | Yes |
| Invoice Date | Date of issue | Yes |
| Buyer's Name & Address | Name and address of the recipient | Yes (B2B) |
| Buyer's GSTIN | GSTIN of the registered recipient (for B2B) | Yes (B2B) |
| HSN / SAC Code | 8-digit code for goods (HSN) or 6-digit for services (SAC) | Yes |
| Description of Goods/Services | Clear description of what is being supplied | Yes |
| Quantity & Unit | Number of items and the unit of measurement (kg, pcs, hrs) | Yes (goods) |
| Taxable Value | Value before applying GST | Yes |
| Tax Rate | Rate of GST applicable (5%, 12%, 18%, 28%) | Yes |
| CGST Amount | Central GST charged (for intra-state) | Yes (intra) |
| SGST Amount | State GST charged (for intra-state) | Yes (intra) |
| IGST Amount | Integrated GST charged (for inter-state) | Yes (inter) |
| Total Invoice Value | Taxable value + total GST | Yes |
| Place of Supply | State where supply is deemed to occur | Yes |
| Signature | Digital or physical signature of authorised person | Yes |
The HSN (Harmonised System of Nomenclature) code is an internationally recognised 8-digit code used to classify physical goods. For example, HSN 0901 covers coffee, while HSN 8471 covers computers. The SAC (Services Accounting Code) is a 6-digit code used to classify services under GST. For example, SAC 9983 covers IT and telecommunications services. Businesses with annual turnover above ₹5 crore must show a 6-digit HSN; smaller businesses can use 4-digit codes.
These two documents are often confused but serve very different purposes under GST law.
| Feature | Tax Invoice | Bill of Supply |
|---|---|---|
| Issued By | Regular GST-registered supplier | Composition taxpayers & exempt supply dealers |
| GST Charged? | Yes — CGST/SGST or IGST shown | No — GST not charged to buyer |
| ITC Available? | Yes, to the buyer | No |
| When Used | Taxable goods and services | Exempt supplies, composition scheme |
| Example | Software company billing a client | A small trader under composition scheme |
The GST invoice requirements differ between business-to-business (B2B) and business-to-consumer (B2C) transactions:
Invoice numbers must follow a consistent serial format within each financial year (April to March). You can use alphanumeric codes (e.g., INV/2025-26/001, GST/101) but the sequence must be unique and must not be repeated or skipped arbitrarily. You can maintain separate series for different categories (e.g., services vs. goods, or different branches) but each series must be internally sequential.
GST law specifies deadlines for issuing invoices. For goods: the invoice must be issued at the time of removal or delivery — generally before or at the point of supply. For services: the invoice must be issued within 30 days of the service being performed (or 45 days for banks and NBFCs). Late invoicing can lead to interest liability on delayed tax payment.
Yes. The GST Act does not mandate a digital or printed invoice. A handwritten invoice with all the mandatory fields is legally valid. However, for ITC purposes, digital invoices are far easier to reconcile and file.
For businesses with annual turnover above ₹5 crore, e-invoicing is mandatory. The invoice is uploaded to the GST portal (IRP — Invoice Registration Portal), which generates a unique IRN (Invoice Reference Number) and a QR code. The printed invoice must carry both. This replaces manual data entry in GSTR-1 as the IRP pushes data directly to GST filings.
Yes. Receipts from GST-registered platforms like Zomato, Uber, and Swiggy are valid tax invoices if they contain all mandatory fields including the GSTIN, HSN/SAC code, CGST/SGST breakup, and invoice number. You can download these from the respective apps for expense claims or ITC purposes.
A Debit Note is issued by the supplier when the invoice value needs to be increased (e.g., additional goods were supplied or a price correction is needed). A Credit Note is issued when the invoice value needs to be reduced (e.g., goods were returned or a discount was agreed after invoicing). Both must reference the original invoice number.
Generate a sample GST invoice for practice — complete with CGST, SGST, HSN codes, and all mandatory fields.
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