GST Invoice Format in India — Complete Guide 2026
GST invoices are the backbone of India's tax compliance system. Whether you're a freelancer, small business owner, or just starting out, understanding the correct GST invoice format is non-negotiable. Get it wrong, and you risk penalties. Get it right, and you've got proof of your transactions for tax authorities.
This guide walks you through every mandatory field, optional details, and common mistakes — so you can create compliant invoices from day one.
What is a GST Invoice?
A GST invoice is a legal document issued by a registered GST supplier to a buyer. It records the transaction details, tax breakdowns, and payment terms. Unlike traditional invoices, GST invoices are mandatory under the Goods and Services Tax system and must follow a strict format defined by the GST Council.
If you're GST-registered, you must issue a GST invoice for every supply (goods or services). If you're not registered but have a registered buyer, you still need to issue one. The format applies whether you're selling physical products, offering services, or both.
Mandatory Fields in a GST Invoice
The GST Council mandates 16 specific fields that must appear on every GST invoice. Missing even one can make your invoice non-compliant.
1. Invoice Number Every invoice must have a unique sequential number. Example: INV-2026-001, or simply 001 if you're tracking separately by month/year. The number must be consecutive — you can't skip numbers or reuse them.
2. Invoice Date The date the invoice is issued. Format: DD/MM/YYYY. This matters because GST is filed monthly, and the invoice date determines which tax period it belongs to.
3. Supplier Details The person/business issuing the invoice must provide:
Name (legal name or trade name)
GST Registration Number (15 digits)
Address (full address of the principal place of business)
State code (2-digit code, e.g., 27 for Maharashtra)
Contact details (optional but recommended: phone, email)
Example: "ABC Digital Services Pvt Ltd, GST Reg: 27AABCT1234A1Z0, Plot No. 42, Sector 5, Panvel, Maharashtra 410206"
4. Buyer/Customer Details Must include:
Name of the recipient
GST Registration Number (if they're GST-registered)
Address (full address)
State code
If the buyer is not GST-registered (consumer), you can skip the GST number but must mention they're unregistered.
5. Ship-To Address (if different) If goods are shipped to a different location than the billing address, provide the complete shipping address with state code.
6. Billing Period If it's a periodic invoice (monthly retainer, subscription), mention the period covered. Example: "For the month of February 2026" or "15 Jan - 15 Feb 2026".
7. Item Description Clearly describe what's being sold:
For goods: product name, variant, model number
For services: service name, duration, scope
HSN Code (if applicable — see article #4 in this series)
Example: "Web Development Service - Homepage Design & Development (5 pages)" or "Laptop Computer - Dell XPS 13, Silver, 512GB SSD"
8. Quantity & Unit
Quantity: How many units (pieces, hours, kg, etc.)
Unit: The measurement (nos./pcs for items, hours for services, kg for goods)
Example: "5 nos." or "40 hours" or "10 kg"
9. Rate/Price (Pre-Tax) The price per unit before GST. This is the base amount.
Example: ₹2,000 per unit or ₹500 per hour
10. Line Item Total (Pre-Tax) Quantity × Rate. This is the subtotal for that line before tax.
Example: 5 nos. × ₹2,000 = ₹10,000
11. Discount (if any) If you're giving a discount, mention it separately. It can be:
Percentage: 10% discount
Fixed amount: ₹1,000 discount
This reduces the taxable value
Example: If line total is ₹10,000 and discount is 10%, taxable amount becomes ₹9,000
12. Taxable Value The amount after discount, on which GST is calculated. This is critical — GST is calculated on this amount, not the original price.
13. CGST, SGST, IGST Rates & Amounts This is where the three GST components appear:
CGST (Central GST): Goes to the Central government
SGST (State GST): Goes to the State government
IGST (Integrated GST): Used for inter-state supplies
Rates depend on the product/service. Common rates are 5%, 12%, 18%, 28%. Some items are 0% (exempt).
Example (for intra-state supply at 18% rate):
Taxable Value: ₹9,000
CGST (9%): ₹810
SGST (9%): ₹810
Total Tax: ₹1,620
Example (for inter-state supply at 18% rate):
Taxable Value: ₹9,000
IGST (18%): ₹1,620
Total Tax: ₹1,620
14. Total Amount (inc. Tax) Taxable Value + Total Tax
Example: ₹9,000 + ₹1,620 = ₹10,620
15. Payment Terms & Due Date When should the buyer pay? Options:
Due on receipt
Net 15 days
Net 30 days
Custom terms
Example: "Payment due within 7 days of invoice date"
16. Terms & Conditions / Notes Any additional information: cancellation policy, payment instructions, bank details, warranty terms, etc.
Optional but recommended: Include your bank account details and UPI ID for easy payment.
Complete Invoice Example
Here's a real-world example to tie it all together:
Common Mistakes to Avoid
Mismatched State Codes — If supplier and buyer are in different states, use IGST (18%), not CGST + SGST. Double-check the state codes.
Missing GST Number — If the buyer is GST-registered, their GST number is mandatory. Missing it can invalidate the invoice.
Wrong Tax Rate — Always verify the correct GST slab for your product/service. A 5% item charged at 18% is a red flag for tax authorities.
Rounding Errors — Calculate taxes correctly to the last paise. Rounding inconsistencies across invoices attract scrutiny.
Duplicate Invoice Numbers — Each invoice number must be unique and sequential. Never reuse numbers, even if you've cancelled an invoice.
Missing Recipient Details — Buyer name and full address are non-negotiable. Vague addresses like "Mr. Sharma, Delhi" won't cut it.
Post-Dated Invoices — Never issue an invoice with a future date. It should match the actual date of supply.
Digital vs. Physical Invoices
GST law recognizes both digital (PDF, email) and physical (printed) invoices as long as they contain all 16 mandatory fields. Digital invoices must be in a standard format (PDF, JSON, or E-Way Bill format).
If you're sending digital invoices, use a tool that generates compliant formats. You can create a free GST invoice at freeinvoicebill.com — no login required. It generates invoices in the correct format, calculates tax automatically, and handles state codes so you don't have to worry about mistakes.
Invoice Storage & Retention
Keep all invoices — issued and received — for at least 6 years. GST authorities can ask for them during audits. Store them digitally in a secure location with timestamps. Physical invoices should be filed chronologically for easy retrieval.
Final Checklist
Before you send an invoice, verify:
Invoice number is unique and sequential
Invoice date is today's date (not future-dated)
Your GST number and registered address are correct
Buyer's GST number is correct (if they're registered)
Item description is clear and specific
Quantity and rate are accurate
Discount is applied correctly (if any)
Tax rate matches the product/service GST slab
CGST + SGST = IGST (for correct calculation)
Total amount is correctly calculated
Payment terms are mentioned
All mandatory 16 fields are present
Getting the GST invoice format right from the start saves you headaches during tax season. It's the difference between smooth filing and scrambling to explain discrepancies to tax authorities.