Is HSN code mandatory on a GST invoice?

Yes for most businesses. Businesses with aggregate turnover up to ₹5 crore must show a 4-digit HSN on invoices to registered buyers, and those above ₹5 crore must show a 6-digit HSN on all invoices.

What is the time limit for issuing a GST invoice for services?

Within 30 days of supplying the service. Banks, insurance companies and NBFCs get 45 days.

Can I issue a handwritten GST invoice?

Yes, if it carries all the mandatory details and you are not required to use e-invoicing. Businesses covered by e-invoicing must generate B2B invoices through the Invoice Registration Portal.

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

A tax invoice shows GST and lets a registered buyer claim credit. A bill of supply shows no GST and is used for exempt supplies and by composition taxpayers.

GST invoice: format, mandatory fields and rules

Updated 11 October 2026

A GST tax invoice is the document a registered business issues when it sells taxable goods or services. Rule 46 of the CGST Rules lists the details it must contain, including both parties' GSTINs, a unique serial number, the HSN or SAC code, the taxable value, the rate and amount of each tax, and the place of supply. A buyer's input tax credit depends on a correct invoice.

Types of GST documents

Document	When it is used
Tax invoice	Sale of taxable goods or services by a regular taxpayer
Bill of supply	Exempt supplies, or any supply by a composition taxpayer (no GST shown)
Receipt voucher	Advance received for services
Refund voucher	Advance returned when no supply is made
Self-invoice and payment voucher	Purchases from unregistered suppliers under reverse charge
Credit note and debit note	Reducing or increasing the value or tax after an invoice, for example on returns or price changes
Delivery challan	Moving goods without a sale, such as job work or sending goods on approval

Mandatory fields on a tax invoice

Name, address and GSTIN of the supplier
A consecutive serial number of up to 16 characters (letters, numbers, hyphen or slash), unique for the financial year
Date of issue
Name, address and GSTIN of the buyer, if registered
For an unregistered buyer, when the taxable value is ₹50,000 or more: the buyer's name and address, and the delivery address with the state name and code
HSN code for goods or SAC for services
Description of the goods or services
Quantity and unit (for goods)
Total value
Taxable value, after any discount or abatement
Rate of tax: CGST, SGST or UTGST, IGST and cess, where applicable
Amount of each tax
Place of supply, with the state name, for inter-state supplies
Delivery address, if different from the place of supply
Whether tax is payable on reverse charge
Signature or digital signature of the supplier or an authorised person

Businesses covered by e-invoicing must also register each B2B invoice on the Invoice Registration Portal and print the QR code it returns.

A sample calculation

Worked example. A Jaipur supplier sells 10 office chairs at ₹1,200 each to a registered buyer in Jodhpur, with a ₹1,000 discount shown on the invoice. GST is 18%.

Value: 10 × ₹1,200 = ₹12,000
Less discount: ₹1,000. Taxable value = ₹11,000
CGST at 9%: ₹990. SGST at 9%: ₹990
Invoice total: ₹11,000 + ₹990 + ₹990 = ₹12,980

Both cities are in Rajasthan, so the invoice shows CGST and SGST. If the buyer were in Ahmedabad, it would show IGST at 18%, ₹1,980, and the place of supply as "Gujarat (24)". The total stays ₹12,980.

When the invoice must be issued

Goods: at or before the time the goods are removed for delivery, or made available to the buyer.
Services: within 30 days of supplying the service. Banks, insurers and NBFCs get 45 days.
Continuous supplies (such as monthly maintenance contracts): on or before the due date of payment, or when payment is received, as per the contract.

How many copies

For goods, the invoice is made in triplicate: the original for the buyer, the duplicate for the transporter and the triplicate for the supplier. For services, two copies are enough. Businesses on e-invoicing do not need a separate transporter copy, since the IRN covers it.

Small retail sales

For a sale below ₹200 to an unregistered buyer who does not ask for an invoice, the shop may skip an individual invoice and issue one consolidated invoice for all such sales at the end of the day.

Credit notes and debit notes

Once an invoice is issued, you do not edit it. Instead:

a credit note reduces the value or tax, for example when goods are returned, a discount is given after the sale, or the invoice overcharged;
a debit note increases the value or tax, for example when the invoice undercharged.

Each note must refer to the original invoice and carry the same kind of details. A credit note for a sale in one financial year must generally be declared by 30 November of the next year, or the date of filing the annual return if earlier, to reduce your tax. The buyer must then reduce its input tax credit by the same amount.

Advances and receipt vouchers

If a customer pays an advance for services before the invoice is raised, you issue a receipt voucher and pay GST on the advance. When the invoice is issued later, the tax already paid is adjusted. For advances received for goods, GST is generally not payable at the time of the advance; it becomes due when the invoice is issued.

Common invoice mistakes

Charging CGST and SGST on an inter-state sale (or IGST on an intra-state one). See CGST, SGST and IGST.
Typing the buyer's GSTIN wrongly, which sends the credit to someone else.
Missing or wrong HSN codes, or reusing a serial number.
Not mentioning reverse charge when it applies.
A composition dealer showing GST on a bill of supply.

Check your tax amounts with the GST calculator. The invoice rules are in chapter VI of the CGST Rules on cbic-gst.gov.in.