GST Invoice Format: Mandatory Fields, Numbering and Time Limits

A GST invoice (called a “tax invoice”) must include every particular listed in Rule 46 of the CGST Rules: your GSTIN, a unique serial number, the date, the buyer’s details, HSN or SAC code, taxable value, tax rate and tax amount. For goods, issue it before or at the time of dispatch; for services, within 30 days of supplying the service. If your turnover is up to ₹5 crore, show a 4-digit HSN code on B2B invoices. Above ₹5 crore, show 6 digits on every invoice.

Getting the format right matters for two reasons. A registered buyer can claim input tax credit (ITC) (the GST paid on purchases that they can set off against their own tax) only with a valid invoice. And your invoices feed straight into your GSTR-1, so errors show up as mismatches later.

What are the mandatory fields in a GST invoice?

Rule 46 lists these particulars. Your billing software should print all of them:

#	Field	Notes
1	Supplier’s name, address and GSTIN	Your registered details
2	Invoice number	Max 16 characters, unique for the financial year
3	Invoice date
4	Recipient’s name, address and GSTIN/UIN	If the buyer is registered
5	Recipient’s name, delivery address, state name and state code	If the buyer is unregistered and the taxable value is ₹50,000 or more (or if a smaller buyer asks for it)
6	HSN code (goods) or SAC (services)	Digits depend on turnover (see below)
7	Description of goods or services
8	Quantity and unit (UQC)	For goods
9	Total value and taxable value	Taxable value after discount or abatement
10	Tax rate and tax amount	Shown separately for CGST, SGST/UTGST, IGST and cess
11	Place of supply with state name	For inter-state supplies
12	Delivery address	If different from place of supply
13	Whether tax is payable on reverse charge	“Yes/No” is enough
14	Signature or digital signature	Not needed on an electronic invoice issued under the IT Act, 2000
15	QR code with IRN	Only if you are covered by e-invoicing

Tip: Intra-state sales show CGST + SGST (half each). Inter-state sales show IGST. Example: an intra-state sale of ₹10,000 at 18% shows CGST ₹900 + SGST ₹900. The same sale to another state shows IGST ₹1,800. A GST calculator can do the split for you.

How should GST invoice numbers be formatted?

The serial number rules are simple but strict:

• Up to 16 characters in total.
• Allowed characters: letters, numbers, hyphen (-) and slash (/), in any combination.
• Consecutive within a series and unique for the financial year.
• You may run one or multiple series, for example JP/25-26/001 for one branch and DL/25-26/001 for another.

Most businesses start a new series on 1 April each year. Credit notes and debit notes should have their own series too.

Watch out: Don’t reuse a number after cancelling an invoice, and don’t skip numbers without a record. Gaps and duplicates are a common question in scrutiny.

What is the time limit for issuing a GST invoice?

Type of supply	When to issue the invoice
Goods (normal sale)	Before or at the time of removal of goods (or delivery, where no movement is involved) – Section 31(1)
Services (general)	Within 30 days of supplying the service – Rule 47
Services by banks, insurers, financial institutions, NBFCs	Within 45 days of supply
Purchases from unregistered suppliers under reverse charge (self-invoice)	Within 30 days of receiving the goods or services – Rule 47A, from 1 November 2024

For reverse charge rules in detail, see our reverse charge guide.

How many HSN digits must I show on an invoice?

This depends on your aggregate turnover in the previous financial year (Notification 78/2020-Central Tax, in force since 1 April 2021):

Previous-year aggregate turnover	B2B invoices	B2C invoices
Up to ₹5 crore	4-digit HSN/SAC (mandatory)	Optional
More than ₹5 crore	6-digit HSN/SAC	6-digit HSN/SAC

The same HSN codes flow into Table 12 of your GSTR-1. From the April 2025 return period, Table 12 is split into separate B2B and B2C tabs, and you must pick HSN codes from a drop-down instead of typing them in. Invoices with wrong or missing HSN codes cause trouble at return time.

Tip: After the GST rate rationalisation that took effect on 22 September 2025, check that each item’s HSN code and rate in your billing software are current. Our guide to the 2025 GST rate changes explains what to update.

What are the rules for B2C invoices?

When you sell to consumers or other unregistered buyers:

• Taxable value of ₹50,000 or more: the buyer’s name, address, delivery address, and state name and code are mandatory.
• Below ₹50,000: these details are needed only if the buyer asks. But for services sold to unregistered buyers through an e-commerce operator, or by suppliers of online information and database services, the buyer’s state name must be on the invoice, whatever the value.
• Very small sales (below ₹200): if the buyer is unregistered and doesn’t want an invoice, you can issue one consolidated invoice at the end of each day. (This option is not available for multiplex cinema tickets.)

Special cases you should know

Exports and SEZ supplies

Export invoices must carry the endorsement “SUPPLY MEANT FOR EXPORT/SUPPLY TO SEZ UNIT OR SEZ DEVELOPER FOR AUTHORISED OPERATIONS UNDER BOND OR LETTER OF UNDERTAKING WITHOUT PAYMENT OF INTEGRATED TAX” (or “ON PAYMENT OF INTEGRATED TAX”, as the case may be). They must also show the recipient’s name and address, the delivery address and the country of destination. Freelancers billing foreign clients should read our guide to GST on export of services.

E-invoicing businesses

If e-invoicing applies to you, your B2B invoice is valid only once it has an Invoice Reference Number (IRN) and QR code. If your turnover has crossed the e-invoice threshold but you are exempt (for example, you are a bank or a GTA), your invoices must carry the declaration in Rule 46(s). See our e-invoicing guide.

Composition dealers and exempt supplies

Composition taxpayers and sellers of only exempt goods or services issue a bill of supply, not a tax invoice, and cannot charge GST on it.

Common mistakes on GST invoices

1. Charging IGST on an intra-state sale (or CGST+SGST on an inter-state sale). Tax paid under the wrong head is not simply adjusted; it needs a refund-and-repay process.
2. Missing the buyer’s GSTIN, or using a wrong one. The buyer’s ITC won’t appear in their GSTR-2B. Check it with our GSTIN validator.
3. Wrong place of supply. This decides whether IGST or CGST+SGST applies.
4. Invoice numbers longer than 16 characters or repeated across branches.
5. Old tax rates after a rate change. Update your item master the day a change takes effect.
6. Issuing service invoices late. Billing more than 30 days after the service was supplied breaks Rule 47 and can shift the time of supply.

What to do next

• Compare your current invoice template against the table above and fix any missing field.
• Check that your HSN digits match your turnover slab and that your rates reflect the September 2025 changes.
• Set up separate series for invoices, credit notes and debit notes from the next 1 April.

If you’d like us to check your invoices and file your returns, our GST return filing service covers both.