GST explained
GST Invoice Format: Every Mandatory Field Under Rule 46, With a Checklist
A GST tax invoice is not just a bill with tax on it. Rule 46 of the CGST Rules lists what it must show, and an invoice that misses a field can cost your customer their input tax credit. This guide goes through every mandatory field, the rules for invoice numbers and HSN codes, the number of copies, and the deadline for issuing the invoice.
Key takeaways
- A tax invoice must carry the supplier’s name, address and GSTIN, a unique serial number of up to 16 characters, the date, the buyer’s details, HSN/SAC, quantity, taxable value, tax rate and amount, and the place of supply.
- Invoice numbers must be consecutive and unique for the financial year; letters, numbers, hyphens and slashes are allowed.
- Businesses with turnover up to ₹5 crore show 4-digit HSN on B2B invoices; above ₹5 crore, 6 digits on every invoice.
- Goods: issue the invoice before or at the time of removal or delivery. Services: within 30 days of supply.
Mandatory fields on a GST tax invoice
Rule 46 sets out the particulars. Grouped the way they appear on a printed invoice, they are:
| Part of the invoice | What must appear |
|---|---|
| Supplier | Name, address and GSTIN of the business issuing the invoice |
| Invoice details | A consecutive serial number unique for the financial year, and the date of issue |
| Buyer (registered) | Name, address and GSTIN or UIN |
| Buyer (unregistered) | Name, address and the state, with the delivery address, when the taxable value is ₹50,000 or more |
| Each line | Description, HSN code (goods) or SAC (services), quantity and unit |
| Values | Total value, taxable value after any discount, rate and amount of CGST, SGST/UTGST, IGST and cess |
| Place of supply | The place of supply, with the state name, for inter-state supplies |
| Delivery | The delivery address if it differs from the place of supply |
| Reverse charge | Whether tax is payable on reverse charge |
| Authentication | Signature or digital signature of the supplier or an authorised person |
An e-invoice generated through the IRP carries an IRN and a QR code and does not need a signature. Businesses above the e-invoicing turnover threshold must report B2B invoices to the IRP; the rest can print invoices from their billing software.
Rules for the invoice number
A common pattern is a prefix plus a running number that resets every April: INV/26-27/0001. Avoid gaps: a cancelled invoice should be cancelled in the system, not deleted, so the number stays accounted for.
- At most 16 characters.
- Letters, digits, the hyphen (-) and the slash (/) only.
- Consecutive within the series, and unique for the financial year.
- You may run more than one series — one per branch, counter or document type — as long as each is consecutive and unique.
In TripleBill each document type and branch has its own numbering series. You can change the prefix and the next number, but only forwards, so a series can never repeat a number.
How many HSN digits do you need?
The digits depend on your aggregate turnover in the previous financial year:
| Turnover in the previous year | B2B invoices | B2C invoices |
|---|---|---|
| Up to ₹5 crore | 4-digit HSN / SAC | Optional |
| More than ₹5 crore | 6-digit HSN / SAC | 6-digit HSN / SAC |
The HSN summary in GSTR-1 is built from the same codes, so a wrong or short code on the invoice shows up again at filing time. Keep the HSN on the item, not typed per bill.
Copies: original, duplicate, triplicate
Printed invoices usually carry the copy name in the top corner. If you share a PDF, the buyer’s copy is the original.
- Goods: three copies — Original for the buyer, Duplicate for the transporter, Triplicate for the supplier.
- Services: two copies — Original for the buyer, Duplicate for the supplier.
When the invoice must be issued
| Supply | Time limit |
|---|---|
| Goods | Before or at the time of removal for delivery, or of delivery itself where there is no movement |
| Continuous supply of goods | Before or at the time of each statement or payment |
| Services | Within 30 days of the date of supply |
| Services by banks, insurers and NBFCs | Within 45 days of the date of supply |
Tax invoice, bill of supply or receipt voucher?
- Tax invoice: a registered person supplying taxable goods or services.
- Bill of supply: exempt supplies, or a composition dealer (who cannot charge GST).
- Receipt voucher: an advance received before the supply.
- Credit note / debit note: correcting the value or tax of an invoice already issued.
A checklist before you print
- 1Your GSTIN and the buyer’s GSTIN are correct (the first two digits are the state code).
- 2The invoice number follows the series and has not been used this year.
- 3Every line has the right HSN/SAC and GST rate.
- 4The tax split matches the place of supply: CGST + SGST within the state, IGST across states.
- 5Discounts shown on the invoice reduce the taxable value.
- 6Reverse charge is marked Yes or No.
- 7The invoice is signed, or it is an e-invoice with an IRN and QR code.
Frequently asked questions
Is HSN code mandatory on a B2C invoice?
For businesses with turnover up to ₹5 crore it is optional on B2C invoices. Above ₹5 crore, a 6-digit HSN is required on every invoice.
Can an invoice number contain letters?
Yes. Letters, digits, the hyphen and the slash are allowed, up to 16 characters, as long as the number is unique for the financial year.
Do I need a signature on a GST invoice?
A printed invoice needs a signature or digital signature. An e-invoice generated through the IRP does not.
What is the time limit to issue a service invoice?
Within 30 days of the supply; 45 days for banks, insurers and financial institutions.
About the author
Written by the TripleBill team, the people who build the billing and accounting software this site is about. We check competitor prices on their own websites on the date shown above, and we say so when our product is the weaker choice. This article is general information, not tax advice.
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Invoices that are right by default.
TripleBill fills every Rule 46 field, picks CGST/SGST or IGST from the customer’s state and keeps your series gap-free.