What a GST invoice must contain
The mandatory fields on a GST tax invoice — GSTIN, serial number, HSN code, taxable value, tax rate and place of supply — and why each one matters at return time.
A GST tax invoice must carry a fixed set of particulars: your name, address and GSTIN, a unique consecutive serial number, the date, the buyer's details, the HSN code, the description, quantity and unit, the taxable value, the tax rate and amount split into CGST and SGST or IGST, the place of supply, and a signature. Miss one and your buyer's input tax credit — and your own return — can be held up.
Last reviewed: August 2026. Rules and thresholds change; confirm the current position with your CA or on the GST portal before you redesign your bill.
What are the mandatory fields on a GST invoice?
The particulars are set out in the invoice rules under GST. Here is the working checklist for a normal tax invoice on goods.
| Field | What goes in it | Why it matters |
|---|---|---|
| Supplier name, address, GSTIN | Your registered legal name and the address on your registration | This is what the buyer matches against the portal |
| Invoice number | A consecutive serial number, unique for the financial year, up to 16 characters, using only letters, numbers, hyphen and slash | Duplicate or broken series is the most common return mismatch |
| Date of issue | The date the invoice is raised | Decides the return period and the credit window |
| Buyer name, address, GSTIN or UIN | Required in full when the buyer is registered | Wrong GSTIN means the credit lands in someone else's ledger — or nobody's |
| Unregistered buyer above the notified value | Name, address, delivery address, state and state code | Applies to higher-value counter sales |
| HSN code | The HSN code for each line, to the number of digits your turnover requires | Drives rate, reporting and the HSN summary in your return |
| Description | Plain description of the goods or services | Should match what you actually shipped |
| Quantity and unit | Quantity with the unit quantity code — PCS, KGS, BOX and so on | A wrong unit quietly corrupts value and stock |
| Total value | Value of the supply before tax adjustments | The headline figure |
| Taxable value | Value after discount, before tax | This is the number tax is charged on |
| Rate of tax | Rate for each of CGST, SGST or UTGST, IGST, and cess where it applies | Line-level, not one rate for the whole bill |
| Amount of tax | Rupee amount for each tax head | Must recompute exactly from taxable value and rate |
| Place of supply with state name | Needed for an inter-state supply | Decides whether you charge IGST or CGST and SGST |
| Delivery address | Where it differs from the place of supply | The bill-to / ship-to case |
| Reverse charge | Whether tax is payable on reverse charge | A yes changes who pays |
| Signature | Signature or digital signature of the supplier or an authorised person | Not needed on an e-invoice carrying a valid digital signature |
If you are covered by e-invoicing, two more things must appear on the printed bill: the Invoice Reference Number (IRN) returned by the portal, and the signed QR code.
How many copies of the invoice do I need?
For goods, three: the original marked Original for Recipient, the duplicate marked Duplicate for Transporter, and the triplicate marked Triplicate for Supplier. For services, two are enough — original for the recipient and duplicate for the supplier. Digital copies count, as long as the trail is intact and retrievable.
Can I use my own invoice number series?
Yes, within limits. The number must be consecutive, unique for the financial year, no longer than 16 characters, and made only of letters, numbers, hyphen and slash. Prefixes for a branch or a shop are fine — MUM/25-26/0143 is a valid number. Restart the series at the start of each financial year and keep one series per book, not a shared pool that two counters draw from at once.
Gaps and repeats are the thing to avoid. A cancelled invoice number should stay cancelled and be reported as such, not reused for the next customer.
When is it a bill of supply instead of a tax invoice?
When you are not charging GST on the supply. Two common cases: you are registered under the composition scheme, or you are supplying goods or services that are exempt or nil-rated. A bill of supply carries most of the same particulars but no tax rate and no tax amount, because there is no tax to pass on.
A composition dealer must also print the declaration that they are a composition taxable person and are not eligible to collect tax on supplies. If you are unsure which document your registration requires, ask your CA — it is a five-minute answer and an expensive mistake.
What about a delivery challan?
A delivery challan moves goods when no invoice is being raised yet — job work, goods sent on approval, stock moving between your own godowns, or supply in instalments where the invoice follows. It carries the date and number, your details, the buyer or consignee details, the HSN code and description, quantity, taxable value where known, and the place of supply.
The rule of thumb: goods move on a challan, value moves on an invoice. Keep the two linked so that when the invoice is finally raised, you can show which challan the goods left on.
What breaks at return time when a field is wrong?
Three fields cause most of the trouble.
The buyer's GSTIN. Type it wrong and the credit shows up against a stranger, or nowhere. Your buyer chases you, you raise a credit note and a fresh invoice, and both of you lose a week.
The place of supply. Charge CGST and SGST on what was actually an inter-state supply and the tax sits under the wrong heads. Fixing it is not a re-print; it is a correction that runs through your returns.
The HSN code and rate. If the code and the rate disagree, the summary in your return will not stand up to a query. Record the code once against the item, not per invoice, so the same product cannot go out at two rates.
What should the invoice total actually be?
Compute each line's taxable value first, apply the rate to that, then sum. Do not compute tax on the invoice total and back it out per line — the paise will not agree with your buyer's records, and small differences across a month of billing become a real reconciliation job.
Worked example. You sell 12 boxes at ₹1,250 a box, with a 5% trade discount shown on the invoice, at an 18% rate, within your own state.
- Gross value: 12 × ₹1,250 = ₹15,000
- Discount at 5%: ₹750
- Taxable value: ₹14,250
- CGST at 9%: ₹1,282.50
- SGST at 9%: ₹1,282.50
- Invoice total: ₹16,815
The discount is deducted before tax because it is shown on the invoice itself. A discount agreed after the sale is a different animal and usually needs a credit note.
How long must I keep the invoice?
Long enough that "we have moved offices" is not an answer. GST prescribes a retention period counted from the due date of the annual return for that year, and your invoices, challans, e-way bills and the underlying stock records all fall inside it. Digital storage is acceptable if the records are complete and can be produced. Check the exact number of years that applies to your registration with your CA.
FAQ
Is a signature compulsory on a GST invoice? Yes, a normal tax invoice needs the signature or digital signature of the supplier or an authorised person. The exception is an e-invoice that already carries a valid digital signature from the portal — that does not need a separate manual signature on the print.
Do I need the HSN code on every invoice? You need it on the invoice lines, and how many digits depends on your aggregate turnover in the previous financial year. Smaller businesses report fewer digits than larger ones. Record the code once against the item so every bill carries the same one.
What if I raise an invoice with the wrong value? Do not edit or delete the original. Issue a credit note to reduce the value, or a debit note to increase it, with a clear reference to the original invoice number and date. Both flow into your returns, so the correction is visible rather than silent.
Can I issue an invoice in a foreign currency? For a domestic supply the tax amounts must be shown in rupees. For an export you may bill in foreign currency, but the value converted to rupees and the tax treatment still have to be reported correctly. Export documentation has its own rules — take your CA's view before the first shipment.
Related reading: CGST and SGST or IGST: how to decide, every time and how to choose inventory software for an Indian SMB.
If you would rather your billing screen enforced these fields than your memory, see what KillStock does out of the box and what it costs.