GST Invoice Generator Guide: Create Compliant Tax Invoices in India

A GST invoice (formally called a tax invoice under GST law) is a document issued by a registered supplier to a recipient when supplying taxable goods or services. It is governed by Section 31 of the CGST Act, 2017 and the GST Invoice Rules (Rules 46–55 of the CGST Rules, 2017).

Who Must Issue a GST Invoice?

• Every GST-registered supplier of taxable goods or services must issue a tax invoice.
• Suppliers under the Composition Scheme cannot issue a tax invoice — they must issue a Bill of Supply instead.
• Suppliers of exempt goods or services must issue a Bill of Supply (not a tax invoice).
• Exporters must issue a tax invoice even though GST rate is zero (exports are zero-rated).

When Must an Invoice Be Issued?

For goods: before or at the time of delivery. For services: within 30 days of the date of supply (45 days for banking and insurance companies). If a supplier fails to issue an invoice within this timeline, it is treated as a violation and may attract penalty.

Threshold for Invoicing

Even if you are not registered for GST (because your turnover is below the threshold — Rs 40 lakh for goods, Rs 20 lakh for services in most states), you may still issue a simple invoice. However, you cannot charge GST or issue a "tax invoice" — only registered persons can do so.

Under Rule 46 of the CGST Rules, a GST tax invoice must contain the following fields. Missing even one mandatory field can invalidate the invoice for ITC purposes.

HSN (Harmonised System of Nomenclature) codes are internationally standardised 8-digit codes used to classify goods. SAC (Services Accounting Code) codes are 6-digit codes used to classify services under GST. Both are mandatory on GST invoices, and the number of digits required depends on your annual turnover.

HSN Code Requirements (Goods)

As of 1st April 2021, the CBIC mandated specific digit requirements more strictly. Always refer to the latest CBIC notification for the current threshold.

How to Find the Right HSN Code

The GST portal (gst.gov.in) has an HSN search tool. You can also refer to the official HSN/SAC rate schedule. Common examples:

• 0901 — Coffee (HSN)
• 6101 — Men's overcoats and jackets (HSN)
• 998311 — Management consulting services (SAC)
• 997211 — Rental of residential property (SAC)

Consequences of Wrong HSN/SAC Codes

Using an incorrect HSN/SAC code can result in: mismatch between your GSTR-1 and the buyer's GSTR-2B, ITC denial to the buyer, and scrutiny notices from GST authorities. In serious cases, it may be treated as tax evasion if a lower-taxed HSN is used for a higher-taxed product.

One of the most important decisions in GST invoicing is determining which tax component to charge — CGST + SGST, or IGST. This depends entirely on whether the supply is intra-state or inter-state.

CGST (Central GST) + SGST (State GST)

Applied on intra-state supplies — where the supplier and the place of supply are in the same state. The total GST rate is split equally between the Centre and the State. For example, on an 18% GST item: CGST = 9% + SGST = 9%.

IGST (Integrated GST)

Applied on inter-state supplies — where the supplier is in one state and the place of supply is in another state. IGST is the full combined rate (not split). For an 18% item in inter-state supply: IGST = 18% (collected entirely by the Centre, which then distributes the state portion to the destination state).

UTGST (Union Territory GST)

Applied instead of SGST for supplies within Union Territories without a legislature (Chandigarh, Dadra & Nagar Haveli, Daman & Diu, Lakshadweep, Andaman & Nicobar Islands). UTs with their own legislature (Delhi, Puducherry, Jammu & Kashmir) use SGST.

Quick Reference Table

GST law prescribes different documents for different supply situations. Using the wrong document type is a compliance error.

Tax Invoice

The standard document for all taxable supplies by a registered supplier. Required for B2B transactions (where the buyer wants to claim ITC) and for B2C transactions above Rs 2.5 lakh in inter-state supplies. Contains all mandatory GST fields including tax breakdown.

Bill of Supply

Used in two situations: (1) Suppliers under the Composition Scheme cannot charge GST, so they issue a Bill of Supply instead of a tax invoice. (2) Suppliers of exempt supplies (goods/services on which GST is nil or exempt) must issue a Bill of Supply. A Bill of Supply explicitly states "This is not a Tax Invoice."

Receipt Voucher

Issued when a supplier receives an advance payment before the actual supply. Must be issued at the time of advance receipt and contain details of the advance amount and applicable tax (if determinable).

Refund Voucher

Issued when an advance is received but the supply is subsequently not made — the supplier refunds the advance and issues a Refund Voucher reversing the Receipt Voucher.

Debit Note

Issued by the supplier when the taxable value or tax charged in the original invoice is less than what should have been charged — e.g., the price was revised upward, or an additional tax amount is due. References the original invoice number.

Credit Note

Issued by the supplier when the taxable value or tax charged in the original invoice is more than what should have been charged — e.g., goods were returned, the price was revised downward, or a deficiency was found. Must be issued within the deadline (before 30th November of the following financial year, or before the date of filing of the annual return, whichever is earlier).

E-invoicing (electronic invoicing) under GST is not about generating an invoice using software — it is a specific process where invoices are authenticated by the Invoice Registration Portal (IRP) operated by GSTN, and a unique Invoice Reference Number (IRN) is assigned to each invoice.

E-Invoicing Threshold (as of FY 2026)

E-invoicing is mandatory for businesses whose aggregate turnover exceeds Rs 5 crore in any financial year from 2017-18 onwards. The threshold has been progressively reduced since e-invoicing was introduced in 2020 (it started at Rs 500 crore).

How E-Invoicing Works

1. The supplier generates the invoice in their accounting software in a standard JSON format prescribed by GSTN.
2. The JSON is uploaded to the IRP (any of the authorised portals — GSTN, NIC, or private IRPs).
3. The IRP validates the data, generates an IRN (a 64-character hash), and adds a digitally signed QR code to the invoice.
4. The supplier then prints or shares the e-invoice (which now contains the QR code and IRN) with the buyer.
5. The IRP simultaneously pushes the invoice data to GSTR-1 and the e-way bill portal — eliminating duplicate data entry.

Exemptions from E-Invoicing

Certain categories are exempt even above the threshold: banking and insurance companies, passenger transportation services, multiplexes (for cinema tickets), and SEZ units (as suppliers, not buyers). These exemptions may be updated — always verify with the latest CBIC notification.

The GST law prescribes specific penalties for invoicing violations. Understanding these helps you appreciate the importance of getting every invoice right.

Key Penalty Provisions

Best Practices to Stay Compliant

• Use invoice generation software or online tools that enforce mandatory fields and auto-calculate GST.
• Keep invoice serial numbers consecutive and never reuse a number within a financial year.
• Maintain all issued invoices for at least 6 years (the limitation period for GST audit).
• Reconcile your GSTR-1 (outward supplies) data with your invoices monthly to catch errors early.
• If you make an error on an issued invoice, issue a Credit Note or Debit Note — never modify or delete the original invoice.