GST Invoice Format in India: The 16 Mandatory Fields (2026)

If you're registered under GST, the invoice you hand a client isn't just a bill — it's the document your buyer uses to claim input tax credit. Get a field wrong and the credit can be denied, which turns a paperwork slip into a real cost for someone you'd like to keep as a customer.

The good news is that the requirements are finite and boring. Rule 46 of the CGST Rules, 2017 lists what a tax invoice must contain, and once you've set it up correctly, it stays correct.

What a GST tax invoice must contain

Rule 46 prescribes 16 particulars. In practice they group into five blocks:

1. Who you are

• Your name, address and GSTIN
• The document must be titled "Tax Invoice" — not "Bill", not "Receipt"

2. The invoice's identity

• A unique serial number, maximum 16 characters, using only letters, numbers, / and -
• The number must run in an unbroken sequence within a financial year
• The date of issue

That sequence requirement catches people out. You cannot skip numbers, and you cannot restart the series mid-year on a whim. If you maintain separate series for different branches or document types, each series must itself be continuous.

3. Who the buyer is

• Name and address of the recipient
• Their GSTIN, if they're registered
• The place of supply (with state name and code) — this is what decides whether you charge CGST + SGST or IGST
• For an unregistered buyer where the invoice value is ₹50,000 or more: name, address, and the state of the recipient are mandatory
• The delivery address, when it differs from the place of supply (bill-to / ship-to cases)

4. What you sold

• Description of the goods or services
• HSN code (goods) or SAC code (services)
• Quantity and unit for goods
• Total value, and the taxable value after any discount

5. The tax

• The GST rate applied
• The tax amount, split into CGST and SGST/UTGST, or IGST, as applicable
• Whether tax is payable on reverse charge
• Signature or digital signature of the supplier or an authorised signatory

Businesses covered by e-invoicing must also carry the IRN and QR code under Rule 48(4).

CGST + SGST, or IGST?

This is the single most common source of wrong invoices, and it comes down to one comparison:

Your state vs. place of supply	What you charge	Example (18% on ₹10,000)
Same state (intra-state)	CGST + SGST, split equally	₹900 CGST + ₹900 SGST
Different states (inter-state)	IGST, the full rate	₹1,800 IGST

The total tax is identical either way — what changes is which government gets it. Charging IGST on a local sale (or the reverse) means an amended invoice and an awkward conversation.

A reliable shortcut: the first two digits of a GSTIN are the state code. If your GSTIN starts with 27 (Maharashtra) and your buyer's starts with 29 (Karnataka), it's inter-state, so IGST. CredHill reads both GSTINs and picks the right one for you, which removes the judgement call entirely.

When must the invoice be issued?

Not whenever you get around to it. Section 31 sets deadlines:

Supply type	Deadline
Goods (involving movement)	Before or at the time of removal of the goods
Goods (no movement)	Before or at delivery / when made available to the buyer
Services	Within 30 days of supplying the service
Services — banks, NBFCs, insurers	Within 45 days

Miss the window and the time of supply is deemed to be the date of the supply itself, not your invoice date — so the GST becomes payable from the earlier date regardless of when you billed.

Tax invoice, or bill of supply?

A tax invoice is for taxable supplies. You issue a bill of supply instead when:

• you're registered under the composition scheme, or
• you're supplying exempt goods or services

A bill of supply carries no tax amount, and it must say so. Composition dealers must also state that they cannot collect tax on supplies.

Five mistakes worth avoiding

1. A broken invoice number series. Gaps invite questions during scrutiny. Let software assign the next number rather than typing it.
2. A missing or wrong HSN/SAC code. These also feed your GSTR-1 HSN summary, so an error here resurfaces at filing time. Storing the code once against each product in an item master is the fix.
3. Wrong place of supply. Especially for services delivered remotely — the rules for the place of supply of services are their own topic, and worth checking rather than assuming.
4. Stale GST rates. The slabs changed substantially in September 2025; see what GST 2.0 actually changed if you haven't revisited your rate list since.
5. Calling a proforma an invoice. A proforma isn't a tax invoice and creates no tax liability — here's the difference between a quotation, a proforma and a tax invoice.

A worked example

A Maharashtra consultancy (GSTIN starting 27) bills a Maharashtra client ₹50,000 for services at 18%:

Field	Value
Taxable value	₹50,000
CGST @ 9%	₹4,500
SGST @ 9%	₹4,500
Invoice total	₹59,000

Same invoice to a Karnataka client (29):

Field	Value
Taxable value	₹50,000
IGST @ 18%	₹9,000
Invoice total	₹59,000

Same total, different split, and only one of them is correct for a given buyer.

The short version

Get these right and you're compliant: the words "Tax Invoice", a sequential number, both GSTINs, the place of supply, HSN/SAC codes, taxable value, the correct CGST+SGST or IGST split, and a signature. Issue it inside the deadline for your supply type.

Doing this by hand in a spreadsheet works until it doesn't — usually at the point where the number series breaks or someone charges IGST on a local sale.

Not tax advice. This is a practical summary of the rules as they stand. For anything unusual — exports, reverse charge, bill-to/ship-to chains, e-invoicing thresholds — check with a chartered accountant.