GST Invoice Format: Mandatory Fields Under Rule 46

What is a GST invoice?

A GST tax invoice is the document a registered business issues when it sells goods or services and charges GST. It does two jobs at once: it tells the buyer what they owe, and it is the document the buyer uses to claim input tax credit on the GST they paid.

That second job is why the format matters. An invoice with a missing GSTIN, a wrong place of supply or a broken number sequence can cost your buyer their credit — and the call that follows comes to you.

The particulars are laid down in Rule 46 of the CGST Rules. You can make an invoice that meets them with the free GST invoice generator, without signing up.

Mandatory fields of a tax invoice (Rule 46)

#	Field	Notes
1	Supplier’s name, address and GSTIN	Your own details, exactly as registered
2	Invoice number	Consecutive, unique in the financial year, up to 16 characters
3	Date of issue
4	Recipient’s name, address and GSTIN	When the buyer is registered (B2B)
5	Unregistered recipient’s details	Name, address, delivery address, state name and code — mandatory when the taxable value is ₹50,000 or more
6	HSN code (goods) or SAC (services)	Digits depend on your turnover, see below
7	Description of goods or services
8	Quantity and unit	For goods
9	Total value of supply
10	Taxable value	After discounts
11	Rate of tax	CGST + SGST/UTGST, or IGST, and cess if any
12	Amount of tax	Shown for each tax separately
13	Place of supply	With state name, for inter-state supplies
14	Delivery address	Where it differs from the place of supply
15	Reverse charge	Whether tax is payable on reverse charge
16	Signature	Or digital signature; not needed on an electronic invoice issued under the IT Act

Two fields deserve a second look.

Place of supply decides the tax. If the place of supply is in your own state, you charge CGST and SGST. If it is in another state, you charge IGST. Charging CGST + SGST on what was really an inter-state sale means the tax went to the wrong government, and fixing it means paying the right tax and claiming a refund of the wrong one.

Taxable value is after discount. If the discount is shown on the invoice, tax is calculated on the reduced value. Calculating tax on the pre-discount amount overcharges the buyer and overstates your output tax.

Invoice numbering rules

Rule 46 is specific about invoice numbers:

• At most 16 characters.
• Only letters, digits, hyphen (-) and slash (/). No spaces, no other symbols.
• Consecutive, with no gaps you cannot explain.
• Unique within the financial year. Most businesses restart the series on 1 April and put the year in the prefix — INV/26-27/0001.
• One or more series are allowed, so separate series per branch or per counter are fine.

A gap in the sequence is not illegal by itself, but you should be able to account for it — a cancelled invoice should stay on record as cancelled rather than disappear.

HSN and SAC code digits

How many digits of HSN you must show depends on your aggregate annual turnover in the previous financial year:

Turnover	B2B invoices	B2C invoices
Up to ₹5 crore	At least 4 digits	Optional
Above ₹5 crore	6 digits	6 digits

Services use SAC codes under the same rule. GSTR-1 now reports HSN summaries separately for B2B and B2C supplies, so using a consistent code on every invoice saves rework at filing time.

How many copies?

• Goods — triplicate. Original for the recipient, duplicate for the transporter, triplicate for the supplier.
• Services — duplicate. Original for the recipient, duplicate for the supplier.

Mark each copy accordingly (“Original for Recipient”, and so on). An e-invoice is generated once on the portal and does not need separate printed copies for this purpose.

When to issue the invoice

Supply	Deadline
Goods that move	Before or at the time of removal for delivery
Goods that do not move	Before or at the time of delivery
Services	Within 30 days of the supply
Services by banks, insurers and NBFCs	Within 45 days

For goods, the practical rule is that the invoice leaves with the truck. If the goods are moving without a sale — for job work or on approval — use a delivery challan instead.

Tax invoice, bill of supply and other documents

Document	When it is used
Tax invoice	Taxable sale by a regular registered business
Bill of supply	Composition dealers, and exempt goods or services — no GST is charged
Receipt voucher	Advance received before the supply (Rule 50)
Debit / credit note	Increasing or reducing the value of an invoice already issued
Delivery challan	Goods moving without a sale (Rule 55)
Proforma invoice	Not a GST document — an offer or a request for advance

A proforma invoice looks like an invoice but is not one. Your buyer cannot claim credit on it, and it does not create a GST liability for you.

Where e-invoicing fits

If your aggregate turnover crossed ₹5 crore in any financial year since 2017-18, your B2B invoices must be reported to the Invoice Registration Portal (IRP) as e-invoices. The IRP returns an IRN and a signed QR code that go on the invoice. Businesses with turnover of ₹10 crore or more must report each e-invoice within 30 days of its date; the portal refuses later reporting.

E-invoicing does not change the fields above. It changes how the invoice is validated.

Mistakes that cost your buyer their input tax credit

• Wrong or missing buyer GSTIN. The invoice will not appear in the buyer’s GSTR-2B, so they cannot claim the credit.
• CGST + SGST on an inter-state sale, or IGST on an intra-state sale.
• A number that breaks the rules — too long, with spaces, or repeated from an earlier invoice in the same year.
• Tax on the pre-discount value.
• The invoice reported in GSTR-1 for the wrong month, so it shows up late for the buyer.

How VyapRise handles GST invoices

VyapRise numbers invoices automatically in a locked, consecutive series, picks CGST + SGST or IGST from the place of supply, and calculates tax on the taxable value after discount. Invoices flow into the GSTR-1, GSTR-3B and HSN summary reports without being typed in again; those reports are on the Pro plan, as PDF, CSV or Excel, with a check of GSTR-1 against the portal’s rules before you or your CA file it. VyapRise does not generate e-invoices (IRN). See pricing for what each plan includes.

To make a single invoice now, use the free GST invoice generator or create a GST bill online. For everyday billing with stock and GST reports in one place, see what the GST billing software includes, what the Free plan covers, and the questions to ask before choosing one.