How to Make a GST Invoice: Format, Rules and a Free Generator
Mandatory fields under CGST Rule 46, CGST/SGST vs IGST, HSN digits, invoice numbering and e-invoicing explained, with a worked example and free generator.
A tax invoice is the document that lets your customer claim input tax credit and lets you prove the tax you collected. If it is missing a mandatory field, uses the wrong tax head or breaks the numbering rules, your buyer's credit can be questioned and you may face a penalty. This guide walks through every field the law asks for, how to decide between CGST + SGST and IGST, and how to number invoices correctly.
Want to skip straight to it? Use the free GST Invoice Generator. It works in your browser, calculates CGST, SGST and IGST automatically from the place of supply, and exports a print-ready PDF. Nothing is uploaded.
Who must issue a GST tax invoice
Every registered person making a taxable supply of goods or services must issue a tax invoice. There are a few variations you should know about:
- Composition taxpayers and suppliers of exempt goods or services issue a bill of supply, not a tax invoice, because they cannot charge GST.
- Advance received before supply needs a receipt voucher; the tax invoice follows when the supply is made.
- Changes after invoicing (returns, price revisions) are handled with a credit note or debit note, never by editing the original invoice.
Mandatory fields under CGST Rule 46
Rule 46 of the CGST Rules, 2017 lists what a tax invoice must contain. In plain terms:
- Supplier's name, address and GSTIN.
- A consecutive serial number (see the numbering rules below).
- Date of issue.
- Recipient's name, address and GSTIN, if the recipient is registered.
- For an unregistered recipient where the invoice value is ₹50,000 or more: name, address, delivery address, and the name and code of the state.
- HSN code for goods or SAC for services (digits depend on turnover, explained below).
- Description of the goods or services.
- Quantity and unit (for goods), for example NOS, KGS, MTR.
- Total value of the supply.
- Taxable value after any discount or abatement.
- Rate of tax: CGST, SGST/UTGST, IGST and cess, as applicable.
- Amount of each tax charged.
- Place of supply, with the state name, for inter-state supplies.
- Delivery address, if different from the place of supply.
- Whether tax is payable on reverse charge.
- Signature or digital signature of the supplier or an authorised representative.
Where e-invoicing applies, the invoice must also carry the Invoice Reference Number (IRN) and the signed QR code returned by the Invoice Registration Portal.
CGST + SGST or IGST? It depends on the place of supply
The tax head is decided by comparing the supplier's location with the place of supply, not with the buyer's billing address alone.
- Intra-state supply (supplier and place of supply in the same state): charge CGST and SGST, each at half the GST rate. In a Union Territory without a legislature, UTGST replaces SGST.
- Inter-state supply (different states), exports and supplies to SEZ units: charge IGST at the full rate.
For goods, the place of supply is usually where the movement of goods ends. For services it is usually the location of a registered recipient, with special rules for things like immovable property, events and transport. When in doubt, check the place-of-supply provisions in the IGST Act or ask your tax adviser.
The first two digits of a GSTIN are the state code, so a quick sanity check is to compare the first two digits of your GSTIN with the buyer's. You can check a GSTIN's structure and checksum with the GST Number Validator.
How many HSN digits do you need?
The requirement depends on your aggregate annual turnover (AATO) in the previous financial year:
| Aggregate turnover (previous FY) | HSN/SAC digits on invoices |
|---|---|
| Up to ₹5 crore | 4 digits on B2B invoices (optional on B2C invoices) |
| Above ₹5 crore | 6 digits on all invoices |
Returns (Table 12 of GSTR-1) have their own, increasingly strict HSN reporting rules, so it is simplest to record the 6-digit code for every item from the start. The HSN/SAC Finder helps you look up codes, but always confirm the code and rate against the CBIC tariff.
GST rates were rationalised from 22 September 2025, with most goods moving into 5% and 18% slabs and a higher rate for a small list of luxury and sin goods. Confirm the current rate for your HSN on the CBIC website or the GST portal before invoicing.
Invoice numbering rules
Rule 46 says the serial number must be:
- Consecutive, in one or more series (for example a separate series per branch or for exports).
- No more than 16 characters long.
- Made of letters, numbers, the hyphen (-) and the slash (/) only.
- Unique for a financial year. Most businesses restart the series on 1 April.
A practical format is prefix + financial year + running number, such as MW/25-26/0001 (13 characters). Avoid spaces, underscores and the hash sign. Never delete a cancelled invoice number; mark it cancelled so the series stays unbroken. The Invoice Number Generator produces compliant series if you want ideas.
E-invoicing: when it applies
E-invoicing means reporting B2B invoices to the Invoice Registration Portal (IRP) to obtain an IRN and QR code. It applies to businesses whose aggregate turnover in any financial year since 2017-18 exceeded the notified threshold. At the time of writing the threshold is ₹5 crore, and taxpayers above ₹10 crore must report invoices within 30 days of the invoice date. These limits have been lowered in stages, so check the current threshold on the GST portal (gst.gov.in) or the e-invoice portal (einvoice.gst.gov.in). A PDF made in any tool, including ours, is not an e-invoice until it is registered on the IRP.
Sample calculation
Suppose a Pune supplier sells two items. Item A: 10 units at ₹500, GST 18%. Item B: 2 units at ₹1,500, GST 5%.
| Line | Taxable value | Intra-state (Pune to Nagpur) | Inter-state (Pune to Indore) |
|---|---|---|---|
| Item A @ 18% | ₹5,000 | CGST 9% ₹450 + SGST 9% ₹450 | IGST 18% ₹900 |
| Item B @ 5% | ₹3,000 | CGST 2.5% ₹75 + SGST 2.5% ₹75 | IGST 5% ₹150 |
| Total | ₹8,000 | Tax ₹1,050, invoice ₹9,050 | Tax ₹1,050, invoice ₹9,050 |
The total tax is the same; only the heads differ. Apply any discount shown on the invoice before calculating tax. You can double-check figures with the GST Calculator.
Step by step with the generator
- Open the GST Invoice Generator and enter your business name, address and GSTIN once; it is remembered in your browser.
- Add the buyer's details and GSTIN, and choose the place of supply.
- Add line items with HSN/SAC, quantity, unit, rate and GST percentage.
- Check that the tool shows CGST + SGST or IGST as expected.
- Set the invoice number and date, mark reverse charge if applicable, add bank and UPI details, and download the PDF.
Common mistakes to avoid
- Charging IGST on a local sale, or CGST + SGST on an inter-state one. The buyer cannot simply adjust one against the other.
- Reusing or skipping invoice numbers within the same financial year.
- Omitting the place of supply or state code.
- Writing a description like "Material" with no HSN.
- Editing an issued invoice instead of issuing a credit or debit note.
Not sure which document to send before the sale? Read Quotation vs Proforma Invoice vs Tax Invoice.
Ready to bill? Create a compliant invoice in a couple of minutes with the free GST Invoice Generator.
Frequently asked questions
What is the maximum length of a GST invoice number?
Sixteen characters. It may contain letters, numbers, hyphens and slashes, must be consecutive and must be unique within a financial year.
When should I charge IGST instead of CGST and SGST?
Charge IGST when the supplier and the place of supply are in different states, and on exports and supplies to SEZ units. Charge CGST and SGST when both are in the same state.
Is HSN code mandatory on every invoice?
Businesses with turnover up to Rs 5 crore must show a 4-digit HSN or SAC on B2B invoices; above Rs 5 crore, 6 digits are required on all invoices. Recording 6 digits for every item is the safest habit.
Is a PDF invoice from an online generator a valid e-invoice?
No. If e-invoicing applies to you, the invoice must be reported to the Invoice Registration Portal to obtain an IRN and signed QR code. Check the current turnover threshold on the GST portal.
Do I need a signature on a GST invoice?
Yes, Rule 46 requires the signature or digital signature of the supplier or an authorised representative. E-invoices registered on the IRP are digitally signed by the portal.