How to Make a GST Invoice: Format, Mandatory Fields and Common Mistakes

If you are registered under GST, every sale you make needs the right document: usually a tax invoice. Get the format right and your customers can claim input tax credit, your returns match your books, and a GST notice is much less likely. Get it wrong and you spend evenings fixing invoices with your accountant.

This guide explains what a GST invoice must contain and the mistakes we see most often in small shops. It is a practical summary, not legal advice. GST rules and rates change, so confirm anything specific to your business with your CA or on the official GST portal.

Tax invoice or bill of supply?

Start with the right document:

A composition taxpayer must also print "composition taxable person, not eligible to collect tax on supplies" on the bill of supply.

The mandatory fields on a tax invoice

Rule 46 of the CGST Rules lists what a tax invoice must show. In plain words:

About you (the supplier)

1. Your name, address and GSTIN

About the invoice 2. An invoice number: consecutive, unique for the financial year, at most 16 characters, using letters, numbers, hyphen (-) or slash (/). Separate series (for example one per counter or branch) are allowed. 3. The date of issue

About the customer 4. Name, address and GSTIN of the customer, if they are registered 5. For an unregistered customer where the invoice value is ₹50,000 or more: their name and address, the delivery address, and the state name and code

About what you sold 6. HSN code for goods or SAC for services (see below for how many digits) 7. Description of the goods or services 8. Quantity and unit (for goods) 9. Total value and taxable value after discounts

About the tax 10. Rate and amount of each tax: CGST and SGST (or UTGST), or IGST, plus cess if it applies 11. Place of supply with the state name, for inter-state sales 12. Delivery address, if different from the place of supply 13. Whether tax is payable on reverse charge

Finally 14. Your signature or digital signature, or that of an authorised person

Good billing software fills in almost all of this automatically once your business details, customer details and item master are set up correctly.

CGST + SGST, or IGST?

This is the most common source of mistakes, and it depends on the place of supply, not on where your customer's GSTIN is from by default:

• Same state (intra-state sale): charge CGST + SGST, split equally. An 18% item becomes 9% CGST + 9% SGST.
• Different state (inter-state sale): charge IGST at the full rate. The same item becomes 18% IGST.

For a walk-in customer buying across your counter, the place of supply is your shop's state, so it is CGST + SGST. For goods you deliver to another state, it is usually IGST.

Charging the wrong type is not a small slip: the tax goes to the wrong government account, and fixing it means paying the right tax and claiming a refund of the wrong one.

How many HSN digits?

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

Using a more detailed code than required is fine. Using the wrong code is not: it can mean the wrong tax rate. Rates are revised from time to time (there was a major rationalisation in September 2025), so check the current rate for each HSN code instead of relying on an old price list.

Rules for retail (B2C) sales

• Small sales: for a sale under ₹200 to an unregistered customer who does not ask for an invoice, you can skip an individual invoice and issue one consolidated tax invoice for all such sales at the end of the day. Most shops simply print a bill for every sale anyway, which is easier to track.
• ₹50,000 or more to an unregistered customer: the customer's name, address and state must be on the invoice (field 5 above).
• Timing: for goods, issue the invoice at or before the time of delivery. For services, within 30 days of providing the service.

Do you need e-invoicing?

E-invoicing means registering each B2B invoice on the government's Invoice Registration Portal (IRP), which returns an IRN (invoice reference number) and a QR code that must appear on the invoice.

It applies to businesses whose aggregate turnover crossed ₹5 crore in any financial year since 2017-18. Most small shops are below this, but if your business is growing, check every year. Starbooks and most modern billing software can produce e-invoice-ready output, but registering on the IRP is a separate step.

Seven mistakes we see in small shops

1. Gaps or repeats in invoice numbers, often from cancelled bills, two counters using the same series, or restarting numbering mid-year. Cancel inside the system rather than tearing up a bill, and give each counter its own series.
2. CGST/SGST charged on inter-state sales (or the reverse).
3. Missing HSN codes, or one generic code for everything.
4. Wrong tax rate for an item after a rate change.
5. No customer GSTIN on B2B invoices, so your customer cannot claim input tax credit and comes back asking for a corrected invoice.
6. Handwritten bills that do not match what is filed. Your GSTR-1 should be built from the same invoices your customers received.
7. Discounts shown wrongly: a discount given on the invoice reduces the taxable value; a discount promised later usually needs a credit note.

A sample layout

                    SRI MURUGAN STORES
       12 Main Road, Tiruvarur, Tamil Nadu 610001
           GSTIN: 33ABCDE1234F1Z5   Ph: 98xxxxxxxx
                       TAX INVOICE
Invoice No: TVR/26-27/01245           Date: 10-10-2026
Customer: Walk-in                     Place of supply: Tamil Nadu (33)
-------------------------------------------------------------
Item              HSN    Qty  Rate    Taxable  GST%   Amount
Toor Dal 1kg      0713   2    150.00   300.00   5%    315.00
Phone charger     8504   1    200.00   200.00   18%   236.00
-------------------------------------------------------------
Taxable value                                    500.00
CGST 2.5% on 300 = 7.50   SGST 2.5% on 300 = 7.50
CGST 9% on 200 = 18.00    SGST 9% on 200 = 18.00
Total                                            551.00
Reverse charge: No            For SRI MURUGAN STORES (Signature)

This is an illustrative example: the shop, GSTIN, items and rates are made up. Always use the current rate for each HSN code.

Let software do the remembering

The simplest way to get GST invoices right every time is to set your items, HSN codes and rates once in billing software and let it handle numbering, CGST/SGST/IGST splits and HSN summaries. Read our checklist on what to look for in billing software for a small shop, and why it matters that it keeps working when the internet drops.