GST Invoice Mandatory Fields: Complete Checklist India 2026

Under the CGST Act 2017 and Invoice Rules, a GST invoice is not just a request for payment—it is a legal document used to claim Input Tax Credit (ITC). If even one mandatory field is missing or incorrect, the tax department can invalidate the invoice, causing your customer to lose their tax credit. For a small business or freelancer, this can lead to strained client relationships and audits.

Mandatory GST Invoice Fields (Complete Checklist)

According to Rule 46 of the CGST Rules, every tax invoice must contain the following information. We've simplified this for the 2026 reporting standards.

#	Mandatory Field	Description / Example	B2C Usage
1	Invoice Serial Number	Must be unique, consecutive, and max 16 chars.	Required
2	Date of Issue	The date the invoice was generated.	Required
3	Supplier GSTIN	Your 15-digit unique GST identification number.	Required
4	Supplier Name/Address	Your registered legal name and principal place of business.	Required
5	Recipient Name/Address	Name and address of the buyer.	Required
6	Recipient GSTIN	Mandatory for B2B; allows the buyer to claim ITC.	N/A
7	HSN / SAC Code	HSN for goods, SAC for services (e.g., 998313).	Required*
8	Description of Items	Clear details of goods sold or services rendered.	Required
9	Taxable Value	Amount after discounts but before GST.	Required
10	GST Rate & Amount	Explicitly mention CGST/SGST or IGST.	Required
11	Place of Supply	Name of the state where supply is made.	Required
12	Signature/Seal	Manual signature or Digital Signature (DSC).	Required

Deep Dive: HSN and SAC Code Requirements

One common area of confusion is the number of digits required in the HSN/SAC code. As of April 2026, the rules are based on your Aggregate Annual Turnover (AATO) in the previous financial year:

• AATO up to ₹5 Crore: 4-digit HSN/SAC is mandatory for B2B invoices. Optional for B2C.
• AATO above ₹5 Crore: 6-digit HSN/SAC is mandatory for all tax invoices (B2B and B2C).
• Chemicals/Specific Goods: 8-digit HSN is often required regardless of turnover.

Interstate vs Intrastate: Getting the Tax Right

If you are in Karnataka and your client is in Maharashtra, you must charge IGST (Integrated GST). If both are in Karnataka, you charge CGST + SGST.

Crucial Rule: If you charge CGST+SGST on an interstate invoice, your client cannot claim credit for it. They will likely ask you to cancel the invoice and issue a fresh one with IGST. Our GST Invoice Generator handles this automatically based on state selection.

The e-Invoicing Mandate (Over ₹5 Crore)

If your annual turnover has ever crossed ₹5 Crore since 2017, you are mandated to generate e-Invoices. This means you must upload your invoice data to the Invoice Registration Portal (IRP) and get an Invoice Reference Number (IRN) and a QR Code, which must be printed on the invoice.

Invoices issued by mandated businesses without the e-invoice QR code are considered legally invalid.

Special Cases: Exports and SEZ

When you export services (e.g., freelancing for a US client), you issue a "Tax Invoice" but with specific modifications:

• LUT (Letter of Undertaking): Most freelancers file an LUT to export without paying tax. The invoice must state: "Supply meant for export under LUT without payment of integrated tax."
• Currency: You can show values in USD, but the total GST values must also be shown in INR using the RBI reference rate of that day.
• Address: Mention the client's full international address and country.

Common Mistakes to Avoid

1. Duplicate Invoice Numbers: Using "001" every month. Invoice numbers must be unique within a single Financial Year (April to March).
2. Wrong Place of Supply: Not checking if the client has multiple offices. Always use the GSTIN address of the office you are billing.
3. Missing Bank Details: While not legally mandatory under GST Act, including your Bank Name, IFSC, and Account Number is "business-mandatory" to get paid!
4. Incorrect Rounding: Total tax amount should be rounded to the nearest rupee.

FAQ: Frequently Asked Questions