Guide · GST
GST invoice format and requirements: what every tax invoice needs
A GST invoice is a legal document, not just a bill. Here are the fields it must carry, how the tax type is decided, and a worked invoice you can check yours against.
Updated · 7 min read
In short
A GST tax invoice must show the supplier's and buyer's details and GSTINs, a unique serial number, the date, HSN or SAC codes, taxable value, tax rates and amounts, and the place of supply. SimpleERP fills these on every invoice automatically.
What must a GST tax invoice contain?
A GST tax invoice must carry the fields set out in the CGST Rules, so the buyer can claim input tax credit and the tax officer can trace the supply. The table lists them with the values from a real-looking example: invoice INV-2026-27-0213 from Lakshmi Steel Furnitures, the fictional Coimbatore business on this site, to Ravi Stores.
| Field | Example |
|---|---|
| Supplier's name, address and GSTIN | Lakshmi Steel Furnitures, 14 Avinashi Road, Peelamedu, Coimbatore 641004, GSTIN 33AAACL1234A1Z5 |
| Invoice number: consecutive, unique for the financial year | INV-2026-27-0213 |
| Date of issue | 03/10/2026 |
| Buyer's name, address and GSTIN (if registered) | Ravi Stores, Big Bazaar Street, Coimbatore 641001, GSTIN 33ABCPR4821K1Z2 |
| Place of supply, with state name and code | Tamil Nadu (33) |
| HSN code for goods, or SAC for services | 9403 |
| Description, quantity and unit | Steel rack 4 shelf, 2 Nos |
| Taxable value, after any discount | ₹9,980.00 |
| Tax rate and amount for each tax | CGST 9% ₹898.20, SGST 9% ₹898.20 |
| Total invoice value | ₹11,776.00 |
| Whether tax is payable on reverse charge | No |
| Signature or digital signature of the supplier or an authorised person | For Lakshmi Steel Furnitures, authorised signatory |
Two more fields apply in some cases: the delivery address when goods are delivered somewhere other than the place of supply, and, for unregistered buyers above a value threshold set in the rules, the buyer's name, address and state.
Illustration of GST tax invoice INV-2026-27-0213 to Ravi Stores with CGST 9% and SGST 9%, round off, a UPI QR code and the amount in words.
How do you decide between CGST + SGST and IGST?
The place of supply decides the tax type: a supply within the supplier's own state carries CGST and SGST in equal halves, and a supply to another state carries IGST at the full rate. The total tax is the same; only who collects it changes.
For goods, the place of supply is generally where the goods are delivered. For services, the general rule looks at the buyer's location, with special rules for things such as property, events and transport. Compare the supplier's state with the place of supply on every invoice.
| Lakshmi Steel sells 2 steel racks to | Place of supply | Tax on ₹9,980 | Invoice total |
|---|---|---|---|
| Ravi Stores, Coimbatore | Tamil Nadu (33), same state | CGST 9% ₹898.20 + SGST 9% ₹898.20 | ₹11,776 |
| A buyer in Kochi | Kerala (32), another state | IGST 18% ₹1,796.40 | ₹11,776 |
The first two digits of a GSTIN are the state code, which is why a business's state can be read straight from its GSTIN: 33 is Tamil Nadu and 32 is Kerala. In union territories without a legislature, UTGST takes the place of SGST.
What are HSN and SAC codes, and how many digits do you need?
HSN codes classify goods and SAC codes classify services, and the code on each line tells the tax officer what was supplied and which rate applies. Steel furniture, for example, falls under HSN 9403.
- The number of digits you must show depends on your annual turnover, under thresholds set by notification.
- The same code feeds the HSN summary in your GSTR-1, so a wrong code on an invoice becomes a wrong line in the return.
- Rates are attached to codes and are revised from time to time, so check the current rate for each of your codes.
When must a tax invoice be issued?
For goods, the tax invoice is issued before or at the time of removal or delivery; for services, it is issued within a period after the service, set by the rules. Issuing late does not change when tax becomes due, so late invoices only create a gap between your books and your GST.
For goods, the invoice is commonly prepared in three copies: the original for the buyer, the duplicate for the transporter and the triplicate for the supplier. For services, two copies are used.
What is the difference between a tax invoice, a credit note and a debit note?
A tax invoice records a taxable supply, a credit note reduces the value or tax of an earlier invoice, and a debit note increases it. Notes must refer to the original invoice.
| Document | Issued when | Effect on GST |
|---|---|---|
| Tax invoice | A registered business makes a taxable supply | Output tax for the supplier, input tax credit for a registered buyer |
| Credit note | Goods are returned, or the price or tax was too high | Reduces the supplier's output tax |
| Debit note | The price or tax was too low | Increases the supplier's output tax |
| Bill of supply | Exempt supplies, or a business under the composition scheme | No GST charged on the document |
What about e-invoicing and e-way bills?
E-invoicing means reporting each B2B invoice to the government's invoice registration portal to receive an IRN and a signed QR code, and it is mandatory for businesses above a turnover threshold notified by the government. An e-way bill is a separate document needed to move goods above a value threshold.
How does SimpleERP make a GST-compliant invoice?
SimpleERP fills the mandatory fields from your setup and your customer record, so the person billing only picks the customer, the products and the quantities.
- Your GSTIN, address and state on every invoice, or the branch's GSTIN and address when you bill from a branch
- The buyer's GSTIN validated, with the state read from it
- CGST and SGST or IGST chosen from the place of supply, switching when the customer changes
- HSN or SAC on every line from the product
- Numbering that follows the April to March financial year and stays within 16 characters until invoice 9,999 of the year
- Round off, amount in words and an optional UPI QR on the A4 print
- Sales register and HSN summary for your accountant's GSTR-1 checks
See it on the GST billing software page, or read the GST compliance page for what SimpleERP does and does not do for your returns.
FAQ
Questions, answered
Is HSN code mandatory on a GST invoice?
Yes, for most businesses. The number of digits you must show depends on your turnover under the current notification. SimpleERP prints the HSN or SAC from the product on every line.
Can I charge IGST on a sale within my state?
Generally no: a supply within the same state carries CGST and SGST. Special cases such as supplies to SEZ units are treated as inter-state. SimpleERP allows IGST within the state for those cases but refuses CGST and SGST on an inter-state supply.
Can I edit a GST invoice after issuing it?
You correct an issued invoice with a credit note or debit note rather than editing it. In SimpleERP a posted invoice is frozen; you cancel it, which reverses its entries, or raise a note against it.
Is the amount in words mandatory on a GST invoice?
It is not among the commonly cited mandatory fields, but most businesses print it because buyers and banks expect it. SimpleERP prints the amount in words in Indian format on every invoice.
Related
Keep reading
GST billing
Tax invoices with CGST, SGST or IGST by place of supply, HSN on every line and a UPI QR on the print.
Read moreGST compliance
Place of supply, HSN summary, registers and the input tax summary, and what is not included.
Read moreMulti-branch accounting
How a small business keeps one set of books across branches: branch tagging, GSTINs by state, stock transfers, branch profit and shared costs.
Read moreWeighted average cost
How weighted average cost values stock and cost of goods sold, with the formula, a worked example and how it compares with FIFO.
Read more
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