Complete Guide to GST Invoicing in India (2026)

The Goods and Services Tax (GST) transformed India's indirect tax system when it was introduced in July 2017. For businesses of all sizes, issuing a GST-compliant invoice is not just a legal obligation — it's the foundation of claiming Input Tax Credit (ITC) and maintaining proper books of accounts. Whether you're a freelancer, small business owner, or run a large enterprise, understanding GST invoicing is essential.

In this comprehensive guide, we'll walk you through everything you need to know about creating proper GST invoices — from mandatory fields and HSN codes to the latest e-invoicing requirements in 2026.

What Is a GST Invoice?

A GST invoice is a document issued by a registered supplier to the buyer at the time of sale. It contains details about the goods or services sold, the applicable tax rates, and the total amount payable. Unlike pre-GST invoices that had varying formats across states, the GST regime mandates a uniform invoice format across India.

Under the GST framework, a tax invoice is required for:

• Every taxable supply of goods or services
• Exports (even zero-rated supplies need an invoice)
• Interstate and intrastate transactions
• Supplies to registered and unregistered persons

Without a valid GST invoice, the recipient cannot claim Input Tax Credit (ITC) — which means they lose the ability to offset taxes paid on purchases against taxes collected on sales.

Mandatory Fields in a GST Invoice

Section 31 of the CGST Act, 2017 and Rule 46 of the CGST Rules define the mandatory contents of a tax invoice. Here's the complete list:

Understanding CGST, SGST, and IGST

One of the most confusing aspects of GST invoicing for new businesses is understanding which tax to charge. The answer depends on one simple question: Is your buyer in the same state as you?

Intrastate Supply (Same State)

When the supplier and buyer are in the same state, you charge CGST (Central GST) + SGST (State GST). Each is half of the total GST rate. For example, if the GST rate is 18%, you charge 9% CGST + 9% SGST.

Interstate Supply (Different States)

When the supplier and buyer are in different states, you charge IGST (Integrated GST) at the full rate. So for an 18% GST item, you charge 18% IGST.

Common GST Rate Slabs

• 0% — Essential items like fresh fruits, vegetables, milk, bread
• 5% — Packaged food, economy class flights, transport services
• 12% — Processed foods, business class flights, IT services
• 18% — Most goods and services (restaurants, telecom, financial services)
• 28% — Luxury items (cars, tobacco, aerated drinks)

HSN Codes: What They Are and Why They Matter

The Harmonised System of Nomenclature (HSN) is an international system of product classification. In India, GST requires businesses to use HSN codes to classify goods on invoices. The number of digits required depends on your turnover:

• Turnover up to ₹5 crore — 4-digit HSN code required
• Turnover above ₹5 crore — 6-digit HSN code required

For services, India uses SAC (Services Accounting Codes), which follow a similar structure. For example, SAC 9983 covers "Other professional, technical, and business services."

Pro tip: You can look up HSN codes on the official GST portal at services.gst.gov.in or use the search feature within most invoicing software.

E-Invoicing Requirements in 2026

India has been gradually rolling out the e-invoicing mandate. As of 2026, e-invoicing is mandatory for businesses with an annual turnover exceeding ₹5 crore. This means your invoices must be reported to the Invoice Registration Portal (IRP) and receive a unique Invoice Reference Number (IRN) and QR code.

How E-Invoicing Works

1. Generate the invoice in your billing software in the prescribed JSON format
2. Upload it to the IRP (Invoice Registration Portal) via API
3. The IRP validates the invoice, generates IRN and QR code, and digitally signs it
4. The signed invoice is returned to you and auto-populated on the GST portal

If your business turnover is below ₹5 crore, you are currently exempt from e-invoicing, but you still need to issue proper GST invoices with all mandatory fields.

Step-by-Step: How to Create a GST Invoice with ProQuote

Creating a GST-compliant invoice doesn't have to be complicated. Here's how to do it in minutes using ProQuote:

1. Open ProQuote and select "Invoice" as your document type
2. Add your business details — company name, address, and GSTIN in the "From" section
3. Add your client's details — their name, address, and GSTIN in the "To" section
4. Set the invoice number — ProQuote auto-generates sequential numbers, but you can customize the format
5. Add line items — for each product or service, enter the description, quantity, rate, and tax percentage
6. Choose your tax type — ProQuote automatically calculates CGST+SGST or IGST based on your selection
7. Add payment details — bank name, account number, IFSC code, and UPI ID
8. Export as PDF — download, print, or share via WhatsApp directly

Common GST Invoice Mistakes to Avoid

Even experienced businesses make these errors. Here are the top mistakes that can lead to ITC rejection or penalties:

• Wrong GSTIN — Always verify your client's GSTIN on the GST portal before issuing an invoice. A single digit error means ITC rejection.
• Missing HSN/SAC codes — These are mandatory and must match the goods/services supplied.
• Incorrect tax split — Charging IGST for an intrastate supply (or vice versa) is a common error.
• Non-sequential invoice numbers — Invoice numbers must be sequential within each financial year. Gaps raise red flags during audits.
• Late invoice issuance — For goods, the invoice must be issued before or at the time of delivery. For services, within 30 days of service completion.
• Missing place of supply — This field determines which state gets the tax revenue and which tax (CGST+SGST vs IGST) applies.

Types of GST Invoices

Not all GST documents are the same. Depending on the transaction type, you may need different document formats:

Tax Invoice

The standard invoice issued for every taxable supply. Required for B2B and B2C transactions where the supply value exceeds ₹200.

Bill of Supply

Issued by businesses registered under the Composition Scheme or for exempt supplies. Does not include tax details since no GST is charged.

Credit Note

Issued when you need to reduce the invoice value — for example, when providing a discount after the invoice was issued, or when goods are returned.

Debit Note

Issued when the invoice value needs to be increased — for example, when the original invoice understated the taxable amount.

Record Keeping Requirements

Under GST law, businesses must maintain invoice records for a minimum of 72 months (6 years) from the due date of filing the annual return. This applies to both issued and received invoices. Digital copies are acceptable, which is why using a tool like ProQuote that lets you export and store PDFs is so practical.

Key Takeaways

• Every taxable supply in India requires a GST-compliant invoice with all 12 mandatory fields
• Use CGST+SGST for same-state sales and IGST for interstate sales
• HSN/SAC codes are mandatory — the digit requirement depends on your turnover
• E-invoicing is required for businesses with turnover above ₹5 crore
• Keep invoice records for at least 6 years
• Use an invoicing tool like ProQuote to ensure compliance and save time