What a GST Invoice Must Contain: A Plain-English Checklist

A GST invoice is more than a bill. For a registered business it is the document the buyer relies on to claim input tax credit, and the document you rely on if the tax department ever asks how you computed your output tax. A missing or wrong detail can cause trouble for both sides. This checklist covers the fields that matter, shows how the tax amounts are worked out, and is clear about what a quick generated invoice leaves out.

This article is general information, not tax or legal advice. The invoice rules are set out in Rule 46 of the CGST Rules, 2017, and they are amended from time to time, so confirm the current text and any notifications with the GST portal, CBIC or a qualified professional before you rely on it.

Who must issue a tax invoice

A registered person supplying taxable goods or services generally issues a tax invoice. Businesses under the composition scheme and those making exempt supplies do not issue a tax invoice in the ordinary sense; they issue a bill of supply instead, and a composition dealer cannot collect GST from the customer. If you are unsure which category you fall in, settle that first, because the rest of this checklist applies to tax invoices.

The checklist

These are the particulars a tax invoice is expected to carry. Treat the list as a working checklist and compare it against Rule 46 for your own case.

1. Supplier details: your name, address and GSTIN.
2. Invoice number: a consecutive serial number, no longer than 16 characters, using letters, numerals, a hyphen or a slash. It must be unique within the financial year. Something like INV-2026/001 works; a number reused across customers does not.
3. Date of issue.
4. Recipient details: for a registered buyer, name, address and GSTIN. For an unregistered buyer, the rule is tied to the invoice value: at Rs. 50,000 or more, name, address and the delivery address with state name and code are needed. Below that, these are recorded only if the buyer asks.
5. Description of goods or services and the HSN code (goods) or SAC code (services). How many digits you must show depends on your turnover and has been changed by notification, so look up the current requirement instead of copying an old one.
6. Quantity and unit for goods, and the total value.
7. Taxable value, after any discount shown on the invoice.
8. Rate of tax and the tax amount, split into CGST and SGST (or UTGST) for a supply within the state, or shown as IGST for a supply between states.
9. Place of supply and other declarations the rules require, such as whether tax is payable on reverse charge.
10. Signature or digital signature of the supplier or an authorised person.
11. E-invoice details where they apply: businesses above the notified turnover threshold must report invoices to the e-invoice system, and the invoice then carries the Invoice Reference Number and a QR code. The threshold has changed over the years, so check the current figure.

When to issue it

For goods, the invoice is issued at or before the time of removal or delivery. For services, it is generally issued within 30 days of the supply. Issuing late can bring penalties and delays the buyer's credit, so make invoicing part of delivery, not a month-end chore.

Worked example: same bill, two kinds of supply

A designer in Pune bills Rs. 25,000 for a service taxed at 18%. The tax amount is Rs. 25,000 × 18 / 100 = Rs. 4,500, so the invoice total is Rs. 29,500.

Line	Client in Maharashtra (same state)	Client in Karnataka (other state)
Taxable value	Rs. 25,000	Rs. 25,000
CGST 9%	Rs. 2,250	–
SGST 9%	Rs. 2,250	–
IGST 18%	–	Rs. 4,500
Invoice total	Rs. 29,500	Rs. 29,500

The total is identical. What changes is how the tax is labelled, and that matters because the buyer claims credit under the head shown on your invoice. A second check at a lower rate: Rs. 40,000 at 5% gives tax of Rs. 2,000 and a total of Rs. 42,000, which splits into Rs. 1,000 CGST and Rs. 1,000 SGST within a state. Always take the rate for your product or service from the current official rate schedule; the rates above are only for illustration.

If the price you quote already includes GST, work backwards: base = total × 100 / (100 + rate). For Rs. 29,500 at 18% the base is Rs. 25,000. The GST calculator adds tax to a base amount and displays an equal CGST and SGST split, so enter the base, not the inclusive price.

What the invoice generator produces

The invoice generator takes an invoice number, seller and buyer names, both GSTINs, one description, a subtotal, a GST rate and a due date. It prints a plain-text "TAX INVOICE" with today's date unless you set one, the tax amount (subtotal × rate) and the total, followed by an authorised-signatory line. For the example above, a subtotal of 25000 and a rate of 18 gives GST of 4500.00 and a total of 29500.00.

That makes it handy for a quick draft, a quotation-style bill or a freelancer who invoices one service at a time. Before sending any invoice, compare the output with the checklist, because some items are not generated.

Limits: what the tool does not cover

• One line item only. There are no quantities, unit prices or per-item rates, so a mixed bill needs a spreadsheet or accounting software.
• No tax split. GST appears as a single figure. It does not show CGST and SGST for an in-state sale or IGST for an inter-state one, so you must add that yourself.
• No HSN/SAC code, place of supply or reverse-charge declaration. Add these by hand where they are required.
• No e-invoice reporting. It does not generate an IRN or QR code or talk to the government portal. Businesses above the e-invoicing threshold need approved software.
• No numbering control. It does not track a series, so keeping numbers consecutive and unique is your job.
• Text output. You copy it into your own document. Nothing is stored or sent anywhere.

A practical routine for small sellers

1. Decide your invoice series for the year (a prefix plus a running number) and never reuse a number.
2. Record the buyer's GSTIN before the first sale, and check the state code, since it decides CGST/SGST versus IGST.
3. Apply discounts before computing tax, and show them on the invoice.
4. Check the margin you actually keep after tax and costs with the profit margin calculator, because GST collected is not your income.
5. Keep a copy of every invoice you issue, and reconcile your sales register with what you report in your returns.

If you are close to an e-invoicing or registration threshold, or you deal in several tax rates, talk to an accountant before choosing your invoicing setup. Errors found later are more expensive than the advice.