What are the mandatory fields on a GST invoice?

A GST invoice must show the supplier's name, address and GSTIN, a unique invoice number and date, the buyer's details, the HSN/SAC code, description, quantity, taxable value, GST rate and amount (CGST/SGST or IGST), place of supply, and the supplier's signature.

What is the time limit to issue a tax invoice?

For goods, issue the tax invoice on or before delivery or removal of the goods. For services, issue it within 30 days of providing the service.

What is the difference between a tax invoice and a bill of supply?

A tax invoice is issued when GST is charged. A bill of supply is issued when no GST is charged — for example by composition-scheme dealers or when selling GST-exempt goods.

How long can a GST invoice number be?

An invoice number can be up to 16 characters. It must be unique and consecutive for each financial year, and can use letters, numbers, dashes and slashes.

What Is a Tax Invoice? GST Invoice Format & Mandatory Fields

Q: What is a tax invoice?

A tax invoice is the legal bill a GST-registered business issues on a sale of goods or services. It records the sale, creates GST liability, and lets the buyer claim input tax credit.

A tax invoice is the most important document in GST billing — it’s the legal bill you issue on every sale. Get its format right and your invoices stay compliant, your customers can claim input tax credit, and your GST returns match up. This guide explains what a tax invoice is, the mandatory fields it must contain, and what a correct GST invoice format looks like.

What is a tax invoice?

A tax invoice is the official bill a GST-registered business issues when it supplies goods or services. Unlike a proforma invoice (which is just an estimate), a tax invoice is a legal document that:

Records the sale in your books and GST returns.
Creates your GST liability — the tax you owe the government.
Lets the buyer claim input tax credit (ITC).

In short, it’s the document that actually counts for tax.

Mandatory fields on a GST invoice

Under GST rules, a tax invoice must contain the following details. Missing fields can make the invoice invalid and block your buyer’s ITC — so this checklist matters:

#	Mandatory field	What it means
1	Supplier details	Your business name, address and GSTIN
2	Invoice number	A unique, consecutive number (up to 16 characters) for the financial year
3	Invoice date	The date the invoice is issued
4	Buyer details	Customer name, address, and GSTIN (if registered)
5	Place of supply	The state where the goods/services are supplied (key for CGST/SGST vs IGST)
6	HSN / SAC code	The classification code for each item
7	Description	What is being sold (goods or services)
8	Quantity & unit	For goods — quantity and unit of measure
9	Taxable value	Value after any discount, before tax
10	GST rate & amount	CGST + SGST (same state) or IGST (other state), and cess if any
11	Total amount	The final amount payable
12	Signature	Signature or digital signature of the supplier

Tip: whether you show CGST + SGST or IGST depends on the place of supply — see CGST, SGST & IGST explained.

What a GST tax invoice looks like

Here’s a simplified sample so you can see how the fields come together.

Header

Field	Example
Supplier	Sharma Traders · GSTIN 27ABCDE1234F1Z5
Invoice No / Date	INV-2026-001 · 06 Jul 2026
Buyer	Verma Stores · GSTIN 27PQRSX6789K1Z2
Place of supply	Maharashtra (27)

Line items

Item	HSN	Qty	Rate	Taxable	GST	Amount
Cotton T-shirt	6109	10	₹300	₹3,000	5%	₹3,150
Ball pen (box)	9608	5	₹200	₹1,000	18%	₹1,180

Totals

	Amount
Taxable value	₹4,000
CGST	₹115
SGST	₹115
Invoice total	₹4,330

(Since buyer and seller are in the same state, GST is split into CGST + SGST. For a different state, it would show a single IGST line instead.)

When must you issue a tax invoice?

Supply type	Issue the invoice…
Goods	On or before delivery / removal of the goods
Services	Within 30 days of providing the service

Issuing on time keeps your GST returns clean and your customer’s ITC intact.

Tax invoice vs bill of supply

Not every sale uses a tax invoice:

Tax invoice — issued when you charge GST.
Bill of supply — issued when you don’t charge GST, e.g. by composition-scheme dealers or when selling GST-exempt goods. It looks similar but shows no tax.

If you’re registered under the regular scheme and selling taxable goods, you issue a tax invoice.

A few good-to-know rules

Invoice numbering: must be unique and consecutive for each financial year (no repeats, no gaps in the series).
Copies for goods: original for the buyer, a copy for the transporter, and one for your records.
Rounding: round the final tax amount to the nearest rupee.

Create compliant invoices in seconds

You don’t need to remember every field. In KhataBuddy, you add the customer and items — and the software fills in the correct HSN code, GST rate, and CGST/SGST or IGST split automatically, generates the invoice number, and lets you share the bill on WhatsApp as a PDF. Every invoice comes out GST-compliant by default. Try KhataBuddy free.