A GST invoice is more than a receipt. The buyer uses it to claim input tax credit, the accountant uses it to file returns, and a missing field can mean a bill is cancelled and issued again. This guide walks through the GST invoice format field by field, when IGST replaces CGST and SGST, and where software saves the checking.
Who wrote this guide
This guide is written by the EZ Solutions team, which builds BillDo, a GST billing app for shops, wholesalers and distributors. It explains the fields in plain language. It is general information, not tax advice: the CGST Rules and a chartered accountant are the reference for any specific business.
What does a GST invoice format include?
A tax invoice issued by a registered business carries the same core fields every time. The CGST Rules list them, and most bills that cause trouble later are missing one of these:
- Seller details: legal or trade name, address and GSTIN.
- Invoice number: a consecutive serial number, unique for the financial year, of up to 16 characters using letters, numbers, hyphens or slashes.
- Invoice date: the date the invoice is issued.
- Buyer details: name and address, and the buyer’s GSTIN when the buyer is registered.
- Goods or services: description, HSN or SAC code, quantity and unit.
- Values: total value, any discount, and the taxable value after discount.
- Tax: the rate and amount of CGST and SGST, or IGST, and any cess.
- Place of supply: the state where the supply is made, with its name, for inter-state sales.
- Reverse charge: whether tax is payable on reverse charge.
- Signature: the signature or digital signature of the supplier or an authorised person.
A delivery address is added when it differs from the place of supply. Everything else on the bill, such as payment terms, bank details or a UPI ID, is useful but optional.
Why each field matters
The fields are not paperwork for its own sake. Each one answers a question someone will ask later:
| Field | Who relies on it |
|---|---|
| Seller and buyer GSTIN | The buyer, to claim input tax credit against the right seller |
| Serial number | The accountant and the tax department, to see that no bill is missing or repeated |
| HSN or SAC code | The seller's returns, where sales are summarised by code |
| Place of supply | Everyone: it decides whether the tax is CGST and SGST or IGST |
| Taxable value and tax amount | The buyer and the seller, so the tax on both sides matches |
CGST and SGST or IGST: how the place of supply decides
The place of supply is the field that changes the tax lines. When the seller’s state and the place of supply are the same, the sale is intra-state: the tax is split equally into CGST and SGST. When they differ, the sale is inter-state and the whole tax is IGST.
Most shops sell within their own state, so CGST and SGST is the usual pattern. Wholesalers and distributors who ship to other states see both. The buyer’s GSTIN helps here, since its first two digits are the state code.
Tax invoice or bill of supply?
Not every bill is a tax invoice. A business under the composition scheme, or one that is not registered, cannot charge GST and issues a bill of supply with no tax lines. So does a registered seller of only exempt goods. The guide to bills of supply and tax invoices covers the difference.
Common mistakes on a GST bill
Most invoice problems come from a short list of slips:
- Broken numbering. Two bills with the same number, or numbers restarted in the middle of a year.
- Wrong state. A buyer from another state billed with CGST and SGST.
- Missing buyer GSTIN. The buyer cannot claim credit without it.
- HSN codes left out. Returns become harder to prepare, since sales are reported by code.
- Tax worked out on the wrong value. Discounts applied after tax instead of before it.
Each of these is easy to make on a handwritten bill book and hard to make when the software fills the fields from stored records.
How BillDo fills the GST invoice format on every bill
BillDo keeps the seller’s GSTIN, address, state and signature in the business settings, the buyer’s GSTIN and state on the party record, and the HSN code and GST rate on each item. When a bill is made, those fields fill in on their own:
- The invoice number comes from a numbering series, assigned at save and never reused; a cancelled bill keeps its number and shows as cancelled.
- The place of supply defaults from the buyer’s state, and BillDo splits the tax into CGST and SGST or IGST from it.
- A GSTIN entered for a party sets the party’s state automatically from the first two digits.
- A business without a GSTIN, or on the composition scheme, gets a bill of supply with no tax lines.
- The A4 template prints every field listed above; A5 and thermal templates are there for counter sales.
The shopkeeper picks the party and items; BillDo works out the taxable value, the tax and the round-off. Bills can be printed, saved as PDF or shared on WhatsApp, and the month’s vouchers go to the accountant’s Tally without re-typing.
A quick check before a bill goes out
Even with software, a few seconds of checking catches the rare slip. Before sending a GST invoice, look at four things: the buyer’s GSTIN, the place of supply, the HSN code on any new item, and the total against what the customer expects. That is usually enough to keep every bill correct the first time.
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