What is a GST Invoice? Format, Mandatory Fields & Rules (2026 Guide)
Everything a registered business must include on a tax invoice under the CGST Rules, with a downloadable-ready checklist.
Why the GST invoice matters
A GST tax invoice is the legal document that lets your buyer claim Input Tax Credit (ITC) and lets you report outward supplies in GSTR-1. A missing field can lead to ITC denial for your customer and penalties for you under Section 122 of the CGST Act.
Mandatory fields under Rule 46
Supplier name, address and GSTIN; a consecutive serial number (max 16 characters); date of issue; recipient name, address and GSTIN (if registered); HSN or SAC code; description, quantity and unit; taxable value with discount; GST rate and amount split into CGST/SGST or IGST; place of supply with state code; whether tax is payable on reverse charge; and signature or digital signature of the supplier.
Invoice numbering rules
Numbers must be unique for a financial year and can contain letters, numerals, hyphens and slashes. Most businesses use a prefix like INV/2026-27/0001. Never reuse or skip numbers; gaps invite scrutiny during audit.
Time limit to issue
For goods, issue the invoice on or before removal or delivery. For services, within 30 days of supply (45 days for banks and NBFCs). Continuous supplies follow the payment due date.
How SmartGST helps
SmartGST Invoices auto-fills every mandatory field, generates sequential numbers, computes CGST/SGST vs IGST from the place of supply and lets you print or share a compliant PDF in one click.
Try it on your next invoice
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Create a free accountKeywords: gst invoice format · tax invoice mandatory fields · rule 46 cgst. This article is general information, not professional tax advice.
