How to Create a GST-Compliant Invoice: The Complete Guide for Indian Businesses

Every mandatory field, every common mistake, and how to get it right the first time

Suresh runs a small manufacturing unit in Rajkot. He’s been filing GST since 2017. Last year, his buyer’s accounts team rejected three of his invoices — not because the goods were wrong, but because his invoices were missing the buyer’s GSTIN and didn’t show IGST and CGST/SGST separately.

The rejection cost him 45-day payment delays on ₹8 lakh worth of invoices. The fix? A GST invoice format that gets it right every time.

What Makes an Invoice ‘GST-Compliant’?

Under the CGST Act, a tax invoice is a legal document. If it doesn’t meet the mandatory requirements, it is not a valid tax invoice — the buyer cannot claim Input Tax Credit (ITC), and the seller may face scrutiny during GST audits.

This matters on both sides of the transaction: incorrect invoices cost buyers their ITC and cost sellers their business relationships.

The 16 Mandatory Fields in a GST Invoice

The CGST Rules specify exactly what must appear on every tax invoice:

1. Supplier name, address, and GSTIN: Your legal name as registered under GST, your registered business address, and your 15-digit GSTIN.
2. Invoice number: A consecutive serial number within the financial year. Cannot be repeated. Should follow a consistent naming pattern (e.g. INV/2026/001).
3. Invoice date: The date the invoice is issued. For services, this must typically be within 30 days of supply.
4. Recipient name, address, and GSTIN (if registered): For B2B supplies, the buyer’s GSTIN is mandatory for ITC claims.
5. Place of supply: The state where the supply takes place. Determines whether IGST (inter-state) or CGST+SGST (intra-state) applies.
6. Whether supply is intra-state or inter-state: Must be explicitly stated.
7. HSN code or SAC code: HSN (Harmonized System of Nomenclature) for goods. SAC (Services Accounting Code) for services. Mandatory for turnovers above ₹5 crore; optional below.
8. Description of goods/services: Clear, specific description. ‘Miscellaneous services’ or ‘goods as discussed’ are not acceptable.
9. Quantity and unit: For goods — number of units, weight, volume as applicable.
10. Taxable value: The price before GST is added.
11. Applicable GST rate: The GST rate (0%, 5%, 12%, 18%, 28%) applicable to each line item.
12. Amount of GST: CGST + SGST (intra-state) or IGST (inter-state). Must be shown separately.
13. Total invoice value: Taxable value + GST. In words and figures.
14. Signature or digital signature: Authorised signatory’s signature. Digital signature accepted for e-invoices.
15. Whether the tax is payable on reverse charge: State Yes/No. Relevant for RCM transactions.
16. Consecutive serial number: Each invoice must have a unique, sequential number within the financial year.

Common mistake: Many small businesses forget to show CGST and SGST as two separate line items for intra-state supplies. Even though they add up to the same total, the split is mandatory for the buyer’s ITC claim.

IGST vs CGST/SGST: When to Use Which

This is the single most common GST billing confusion:

• Intra-state supply (supplier and buyer in same state): Use CGST + SGST. Each is half the total GST rate. For 18% GST: 9% CGST + 9% SGST.
• Inter-state supply (supplier and buyer in different states): Use IGST. The full GST rate as a single line item. For 18% GST: 18% IGST.

The ‘Place of Supply’ field determines which applies. It defaults to the buyer’s state for most B2B goods transactions.

Common GST Invoice Mistakes That Trigger ITC Rejection

• Missing buyer GSTIN on B2B invoices
• Wrong HSN/SAC code — buyer can’t claim ITC with mismatched codes
• CGST and SGST not shown as separate amounts
• Invoice date more than 30 days after the service was rendered
• Incorrect place of supply (IGST vs CGST/SGST error)
• No consecutive numbering — gaps in invoice sequence raise audit flags
• Taxable value and total value not clearly distinguished

B2C Invoice vs B2B Invoice: What’s Different

For supplies to unregistered buyers (B2C), the requirements are slightly relaxed:

• Buyer’s GSTIN not required (they’re not registered)
• Recipient address is optional for invoices below ₹50,000
• A simplified invoice is allowed for supplies below ₹200

However, the seller must still maintain all records and the invoice must include all other mandatory fields.

The Easiest Way to Get It Right Every Time

The fastest solution is to use a GST bill generator that has all 16 mandatory fields pre-built, calculates IGST vs CGST/SGST automatically based on supply type, and validates your inputs before generating the PDF.

You enter the data — business name, client details, line items, GST rate. The generator handles the format, calculations, and compliance requirements.

🔗 Free GST Bill Generator — mybooksai.app — Create a GST-compliant bill free — all 16 mandatory fields included

E-Invoicing: Who Must Comply?

If your aggregate annual turnover exceeds ₹5 crore, e-invoicing is mandatory. This means your invoices must be generated through the GST portal’s Invoice Registration Portal (IRP), which assigns each invoice an IRN (Invoice Reference Number) and a QR code.

Below ₹5 crore, e-invoicing is optional. Standard printed or PDF invoices with all mandatory fields remain fully compliant.

Record-Keeping Requirements

• Keep all tax invoices for a minimum of 6 years from the date of filing the annual return
• Digital copies (PDF) are legally equivalent to physical copies
• Invoice numbers must be sequential — no retroactive generation or backdating
• Amended invoices must reference the original invoice number

Practical Takeaway

GST invoicing compliance is not optional — but it doesn’t have to be complicated. The key is to use a format that has the right fields, calculates the right taxes, and produces a document that stands up to scrutiny from both your buyer’s accounts team and the GST department.

Get your GST bill generator set up once, use it consistently, and invoicing becomes a 2-minute task for every transaction.

🔗 Free GST Bill Generator — mybooksai.app — Free GST Bill Generator — create and download compliant invoices instantly

About MyBooksAI

MyBooksAI is a free AI-powered cloud accounting platform built for Indian SMEs and emerging market businesses. It includes free tools for GST billing, UPI QR generation, purchase orders, quotations, and proforma invoices — no signup required for the tools. For full accounting automation, visit mybooksai.app.