GST invoice format: every field a tax invoice must have

Tax invoice or bill of supply?

A business registered under GST that charges tax issues a tax invoice. A business under the composition scheme cannot collect GST from customers, and a business that supplies only exempt goods or services has no tax to charge; both issue a bill of supply instead, which has the same details apart from the tax lines.

If you are not registered for GST at all, you can still give a simple invoice, but it must not show any GST and must not carry a GSTIN.

The fields every tax invoice needs

The GST rules list what an invoice must contain. In practice, check for all of these:

• Your business name, address and GSTIN.
• An invoice number and the date of issue.
• The customer's name and address, and their GSTIN if they are registered.
• The place of supply, with the state name and code, when the supply is between states.
• A description of each item, with its HSN code for goods or SAC code for services.
• Quantity and unit for goods, and the rate per unit.
• The taxable value of each line after any discount.
• The GST rate and the tax amount, shown as CGST and SGST, or as IGST.
• The invoice total, and whether tax is payable on reverse charge.
• Your signature or digital signature, or that of an authorised person.

How to number invoices

Invoice numbers must run in one consecutive series for each financial year, be unique within that year, and be no longer than 16 characters. Letters, numbers, hyphens and slashes are allowed, so formats like INV-001 or 26-27/045 both work. You may run separate series, for example for different branches, as long as each is consecutive.

Do not skip or reuse numbers. If you cancel an invoice, keep the number as cancelled in your records rather than giving it to a new one. Starting a new series each April, with the year in the prefix, keeps things tidy.

CGST and SGST or IGST

The split depends on where you are registered and the place of supply. If both are in the same state, the GST rate is split equally into central and state tax: an 18% rate becomes 9% CGST and 9% SGST. If they are in different states, the full rate is charged as IGST. The customer pays the same total either way, but choosing wrongly means the tax went to the wrong government, which takes paperwork to fix.

The first two digits of a GSTIN are the state code, which is a quick way to check: 27 is Maharashtra, 29 is Karnataka, 07 is Delhi. The GST invoice generator reads the code from the customer's GSTIN, picks the right split, and checks the GSTIN's last character so typing mistakes are caught before the invoice goes out.

HSN and SAC codes

Businesses with turnover up to ₹5 crore must show at least 4-digit HSN codes on invoices to registered customers; above ₹5 crore, 6 digits are required. Services use SAC codes, which usually start with 99. The rate you charge depends on the code, so look up the current rate for each item, especially after the 2025 changes that moved most goods to the 5% and 18% slabs.

If you want to check an amount before writing the invoice, the GST calculator adds or removes GST from any price.

When to issue the invoice

For goods, issue the invoice at or before the time they are removed or delivered. For services, issue it within 30 days of providing the service. Larger businesses, with annual turnover above ₹5 crore, must create e-invoices for business customers through the government's invoice registration portal, which adds an IRN and QR code. A PDF from any generator is not a substitute for that.

Mistakes that come back later

Most invoice problems show up months later, when the customer files a return or reconciles credit. Watch for these:

• Wrong customer GSTIN: the customer cannot claim credit, and you will be asked to amend the invoice.
• Wrong state: CGST and SGST charged on an inter-state sale, or the other way round.
• Rounding errors: tax worked out on the total instead of each line, so the figures do not match the return.
• Gaps or repeats in the invoice series.
• No amount in words, or a total that does not match the lines.

Get paid faster

A clear invoice also helps you get paid on time. Add your bank details or a UPI ID, and send a fixed-amount UPI QR code with the invoice so the customer cannot change the amount when they scan it.