GST invoice rules: mandatory fields under Rule 46 (with example)

A GST invoice does two jobs at once. It is your bill to the customer, and it is the document your registered customer needs to claim input tax credit. If a required detail is missing, your buyer may lose that credit and come back to you to fix it.

The good news: the government does not force one fixed layout. The CBIC’s own guidance says plainly that “there is no format prescribed for an invoice”. What the law does fix is the list of details, called particulars, in Rule 46 of the CGST Rules, 2017. This guide walks through that list, the numbering rules, HSN digits, timing, and a worked example.

Who must issue a tax invoice

Every GST-registered business that makes a taxable sale issues a tax invoice (Section 31 of the CGST Act). There are two common exceptions:

• If you are under the composition scheme, or you sell only exempt goods or services, you issue a bill of supply instead, because you cannot charge GST. See our composition scheme guide.
• If you sell both taxable and exempt items to an unregistered customer, you may issue a single invoice-cum-bill of supply.

The mandatory fields under Rule 46

Here is the list, in plain words. Only the fields that apply to a sale are needed. For example, a shop selling inside its own state never fills “place of supply for inter-state sales”.

#	Field	What it means in practice
1	Your name, address and GSTIN	Exactly as on your registration certificate.
2	Invoice number	Consecutive, unique for the financial year, up to 16 characters. One or more series allowed.
3	Date of issue	The date you issue the invoice.
4	Customer’s name, address and GSTIN	GSTIN (or UIN) if the customer is registered.
5	Unregistered customer’s details	Name, address, delivery address and state name with code, when the taxable value is ₹50,000 or more.
6	HSN code (goods) or SAC (services)	Number of digits depends on your turnover (see below).
7	Description	What you sold.
8	Quantity and unit	For goods, e.g. 2 NOS, 5 KGS.
9	Total value	Value of the supply.
10	Taxable value	After discount or abatement, if any.
11	Rate of tax	CGST, SGST/UTGST, IGST and cess, as applicable.
12	Amount of tax	Shown separately for each tax.
13	Place of supply	With the state name, for inter-state sales.
14	Delivery address	When it differs from the place of supply.
15	Reverse charge	Whether tax is payable on reverse charge.
16	Signature	Signature or digital signature of you or your authorised person.

Two more items apply only to bigger businesses: the IRN and QR code for e-invoices (turnover above ₹5 crore), and a QR code on B2C invoices for very large businesses. We cover e-invoicing in its own guide: E-invoicing in GST.

The 16-character invoice number rule

Your invoice number can use letters, numbers, the hyphen “-” and the slash “/”. It must be:

• consecutive within each series,
• unique for the financial year (April to March), and
• no longer than 16 characters in total.

INV/2026-27/0042 is exactly 16 characters, so it is fine. INVOICE/KOL/2026-27/00042 is too long. You can run separate series, for example one per branch or one for credit notes, as long as each one follows the same rules. Skipping or reusing numbers is a common reason for questions from the department, so let your billing software assign them rather than typing them by hand.

How many HSN digits you need

Notification 78/2020–Central Tax set the minimum digits from 1 April 2021, based on your aggregate turnover in the previous financial year:

Turnover in the previous year	Minimum HSN/SAC digits
Up to ₹5 crore	4 digits (may be left out on invoices to unregistered customers)
More than ₹5 crore	6 digits on every invoice

These are minimums. You may always show a longer, valid code. A separate rule, Notification 90/2020–Central Tax, requires the full 8-digit code for a list of specified chemicals regardless of turnover. If you are not sure which code fits, start with our HSN code finder and read HSN and SAC codes: how to find the right code.

CGST + SGST or IGST?

The tax lines depend on where the sale happens:

• Same state as you (intra-state): show CGST and SGST (or UTGST), each at half the rate. An 18% item becomes 9% CGST + 9% SGST.
• Another state (inter-state): show IGST at the full rate, and write the place of supply with the state name.

Getting this wrong means paying the right tax again and claiming a refund of the wrong one, so it is worth understanding properly: see CGST, SGST and IGST explained.

When to issue the invoice

• Goods: before or at the time the goods are removed for delivery, or made available to the buyer when there is no movement.
• Services: before or after providing the service, but within 30 days of the supply (Rule 47). Banks, insurers and some financial institutions get 45 days.
• Continuous supplies (for example, monthly maintenance) follow the due date of payment or the billing milestone in the contract.

Small sales below ₹200

You need not issue a separate invoice for a sale below ₹200 to an unregistered customer who does not ask for one. You must still issue a consolidated invoice for all such sales at the end of each day.

How many copies

For goods, the rules ask for three copies: Original for Recipient, Duplicate for Transporter and Triplicate for Supplier. For services, two copies: Original for Recipient and Duplicate for Supplier. Most billing software prints the copy label for you.

Worked example: an electronics shop in Kolkata

Rupa Electronics in Kolkata (West Bengal, state code 19) sells to Das Traders, a registered business in Howrah, also in West Bengal. Rupa’s turnover last year was ₹1.2 crore, so 4-digit HSN codes are enough. Since buyer and seller are in the same state, the invoice shows CGST + SGST.

Item	HSN	Qty	Rate (₹)	Taxable value (₹)	GST rate
LED TV 43”	8528	2 NOS	28,500.00	57,000.00	18%
HDMI cable 2 m	8544	5 NOS	450.00	2,250.00	18%
Total taxable value				59,250.00
CGST @ 9%				5,332.50
SGST @ 9%				5,332.50
Invoice total				69,915.00

Around this table, the invoice also shows Rupa’s name, address and GSTIN, the number INV/2026-27/0042, the date, Das Traders’ name, address and GSTIN, “Tax payable on reverse charge: No”, and a signature (not needed if the invoice is issued electronically).

If Das Traders were in Patna instead, the same invoice would show IGST @ 18% = ₹10,665.00 and “Place of supply: Bihar (10)”. Want to try your own numbers? Use the GST calculator or the free GST invoice generator, and check a customer’s number with the GSTIN validator.

Common mistakes to avoid

1. Typing the customer’s GSTIN by hand. One wrong character and their credit will not show up. Validate it before you bill.
2. Wrong tax type. Charging IGST on a local sale, or CGST + SGST on an inter-state one.
3. Gaps or repeats in numbering, especially when two people bill from two computers.
4. Missing HSN codes on B2B invoices, or too few digits once turnover crosses ₹5 crore.
5. Changing an invoice after it is issued. Corrections should go through a credit note or debit note that refers to the original invoice.
6. Forgetting e-invoicing when your turnover crosses ₹5 crore.

How software helps

A ready-made layout saves time: our GST invoice format template shows every field in place. If you bill every day, GST billing software does the checking for you. In Invoiqo, for example, each product carries its HSN code and GST rate, the tax type is picked from the customer’s state, and invoice numbers run in a locked sequence for each financial year, so two people billing at once never clash.

In short

Your invoice can look however you like, but it must carry the Rule 46 details, a clean 16-character number series, enough HSN digits and the right tax type. Get those right and your customers can claim their credit without a phone call to you. When you are ready to stop checking each bill by hand, you can compare Invoiqo’s plans, including a free plan.