How to Create a GST Invoice — Step-by-Step Guide

A GST invoice is a tax invoice issued by a GST-registered seller that lists the taxable value, the GST rate, and the tax split (CGST/SGST or IGST) for every item or service sold. This guide walks through each mandatory field and a full worked example, so you can create one correctly the first time.

What must a GST invoice include

The GST law doesn't prescribe a fixed layout, but it does require a specific set of fields on every invoice you issue once you're GST-registered:

• Invoice number and date — a unique, sequential number for the financial year
• Seller details — your business name, address, and GSTIN
• Buyer details — name and address, plus GSTIN if the buyer is GST-registered (B2B)
• HSN or SAC code — for each line item (goods use HSN, services use SAC)
• Description, quantity, and rate — for every item or service billed
• Taxable value — the amount before tax
• GST rate and split — CGST + SGST (same state) or IGST (different states)
• Total invoice value — taxable value plus tax

Missing any of these fields is the most common reason a GST invoice gets rejected during a client's input tax credit reconciliation, so it's worth treating this list as a checklist rather than a guideline.

Invoice numbering rules

Invoice numbers must be sequential and unique for each financial year — you can restart the series on 1 April, but you can't skip numbers or reuse one within the same year. Most businesses use a prefix plus a running number, like INV-2026-001, to keep the series readable and audit-friendly.

CGST/SGST vs IGST — which applies to your invoice

This depends entirely on where the buyer is located relative to you, not on what you're selling:

• Same state (intra-state supply): split the GST rate equally into CGST (central) and SGST (state) — for example, an 18% rate becomes 9% CGST + 9% SGST.
• Different states (inter-state supply): charge the full rate as IGST — an 18% rate becomes 18% IGST, paid as a single line.

The total amount of tax collected is identical in both cases — only how it's split and reported differs.

Worked example: a freelance design invoice

A freelance web designer in Pune invoices a client also based in Maharashtra (intra-state supply) for a website design project:

• Service: Website design (SAC 998314)
• Taxable value: ₹30,000
• GST rate: 18%
• CGST (9%): ₹2,700
• SGST (9%): ₹2,700
• Total invoice value: ₹35,400

If the same client were based in Delhi instead (inter-state supply), the designer would charge IGST at 18% (₹5,400) as a single line instead of splitting CGST/SGST — the total stays ₹35,400, only the tax breakdown changes.

GST invoice vs bill of supply

Not every sale gets a GST invoice. If you're registered under the composition scheme, or if what you're selling is exempt from GST, you issue a bill of supply instead — it looks similar but has no tax rate, tax amount, or CGST/SGST/IGST split, since no tax is being charged. Issuing a full GST invoice when a bill of supply was required (or vice versa) is a common compliance slip for businesses that deal in both taxable and exempt supplies.

How many copies does a GST invoice need

For goods, GST rules specify three copies — original for the buyer, duplicate for the transporter, and triplicate for the seller's own records. For services, only two copies are required — original for the recipient and duplicate for the supplier. In practice, almost every freelancer and agency issues invoices digitally now, so "copies" just means keeping a saved record on both sides rather than printing multiple physical sheets.

Common mistakes that make an invoice non-compliant

• Missing or wrong GSTIN — double-check the buyer's GSTIN for B2B invoices; an invalid GSTIN blocks their input tax credit claim.
• Wrong tax split — charging CGST/SGST on an inter-state supply (or vice versa) is a frequent error when billing out-of-state clients.
• Skipping the HSN/SAC code — required once your turnover crosses the applicable threshold, regardless of invoice value.
• Non-sequential numbering — restarting or skipping numbers outside the financial-year boundary breaks the audit trail.

If you're unsure which HSN or SAC code belongs on a line item, see how to find your HSN code as a freelancer before finalizing the invoice. For the full list of required fields — including the conditional ones like reverse charge and place of supply — see the GST invoice mandatory fields checklist. To see how these fields are laid out section by section, with a sample you can download, see the GST invoice format explained.

Creating the invoice without doing the math by hand

You can build a GST invoice in a spreadsheet, but you're responsible for getting the CGST/SGST/IGST split, the rounding, and the running total right on every single one. The GST Invoice Generator auto-calculates the correct tax split from the supply type and rate, so the math errors above simply can't happen — enter the details once and download a compliant invoice as a PDF.

For freelancers and agencies issuing these regularly, see Dharayana plans to save client details, reuse line items, and keep every invoice numbered sequentially without tracking it manually.

Frequently asked questions

What is the minimum information a GST invoice must have?

Invoice number and date, your name/address/GSTIN, the buyer's name/address/GSTIN (if registered), HSN or SAC code, description/quantity/rate of goods or services, taxable value, applicable GST rate split into CGST/SGST or IGST, and the total invoice value.

Can I create a GST invoice without accounting software?

Yes. A spreadsheet or a free online generator works as long as every mandatory field is present and the tax is calculated correctly. Software just removes the manual math and formatting risk as your invoice volume grows.

What's the difference between CGST/SGST and IGST on an invoice?

CGST and SGST apply together when the buyer and seller are in the same state (intra-state supply), splitting the GST rate equally between the two. IGST applies as a single tax when the supply crosses state lines (inter-state supply). The total tax amount is identical either way.

Do I need to issue a GST invoice if I'm not GST-registered?

No. Only GST-registered businesses issue GST invoices. If your turnover is below the registration threshold and you haven't registered voluntarily, a regular bill or receipt without GST fields is sufficient.

Is there a specific format the GST invoice must follow?

No fixed template is prescribed, but every mandatory field must be present and invoice numbers must follow a consistent, sequential series. Beyond that, you can design the layout to match your brand.

Ready to put this into practice? Try the GST Invoice Generator — it's free, requires no login, and downloads straight to PDF.