GST invoice format: what a tax invoice must include

If you are registered under GST, every taxable sale needs a proper tax invoice. The details it must contain are set out in the GST rules, and a missing GSTIN, a wrong place of supply or a broken number sequence can cost your customer their input tax credit or cause trouble in an audit. This guide walks through every field and the rules around numbering, tax split and copies.

Fields a GST tax invoice must show

1. Supplier details: your name, address and GSTIN.
2. Invoice number: a consecutive serial number, unique for the financial year, up to 16 characters (letters, numbers, hyphen and slash are allowed).
3. Invoice date.
4. Recipient details: name, address and GSTIN if the customer is registered. For an unregistered customer, include name and address (with the state) when the taxable value is ₹50,000 or more.
5. Place of supply with the state name and code, for inter-state supplies.
6. Delivery address, if different from the place of supply.
7. HSN code for goods or SAC for services.
8. Description, quantity and unit of the goods or services.
9. Total value, any discount, and the taxable value.
10. Tax rate and amount: CGST and SGST (or UTGST), or IGST, and cess if any.
11. Whether tax is payable on reverse charge.
12. Signature or digital signature of the supplier or an authorised person.

CGST + SGST or IGST?

Compare your state (the first two digits of your GSTIN) with the place of supply:

• Same state: charge CGST and SGST, each at half the rate. For 18% GST that is 9% + 9%.
• Different states: charge IGST at the full rate.

For goods, the place of supply is usually where the goods are delivered. For most services to a registered business, it is the customer’s location. The GST Invoice Generator picks the split from the two states and lets you override it.

How many HSN digits?

Businesses with an aggregate turnover of up to ₹5 crore in the previous year must show 4-digit HSN codes on B2B invoices; above ₹5 crore, 6 digits. Service codes (SAC) start with 99.

GST rates

Since 22 September 2025 (“GST 2.0”), most goods and services fall in the 5% and 18% slabs, with a 40% rate for luxury and sin goods. Special rates such as 0.25% and 3% remain for a few items, and many essentials are exempt. The GST Calculator works out tax for any rate.

Numbering your invoices

Use one continuous series per financial year (April to March), for example INV/26-27/001, INV/26-27/002. Never reuse or skip numbers without a record. You may run separate series for different branches or types of supply, as long as each is consecutive and unique.

Other documents you may need

• Bill of supply: issued instead of a tax invoice by composition dealers, or for exempt supplies; it shows no tax.
• Credit and debit notes: to correct an invoice after it is issued (returns, price changes), referring to the original invoice.
• E-invoice (IRN): businesses above the notified turnover limit (₹5 crore at the time of writing) must report B2B invoices on the Invoice Registration Portal and print the IRN and QR code on them.
• E-way bill: generally required when goods worth more than ₹50,000 are moved.

Common mistakes

• Typing the customer’s GSTIN wrong: the generator checks the format and check digit.
• Charging CGST + SGST on an inter-state sale (or IGST on an intra-state one).
• Missing HSN/SAC codes or the reverse charge statement.
• Rounding tax per line inconsistently: keep CGST and SGST equal and round the total to the nearest rupee if you round at all.