GST Invoice Format: What Every Compliant Invoice Must Include

A GST-compliant invoice needs a specific set of fields, and most of them aren't optional extras: the seller's name, address and GSTIN, a unique sequential invoice number, the invoice date, the buyer's details, the HSN or SAC code for whatever you're selling, a clear description, the taxable value, the tax rate split correctly as CGST plus SGST or as IGST, the tax amount in rupees, the place of supply, and a signature. This isn't a suggested format. It's what the law requires for the invoice to count as valid documentation for both parties' tax filings.

Most small business owners get the obvious parts right: name, address, amount. Where they trip up is on two or three fields that look minor and aren't: place of supply, the CGST/SGST versus IGST split, and HSN codes. Get any of those wrong and the invoice is technically non-compliant, even if the total rupee amount on it is perfectly correct.

The fields a GST invoice legally needs

Here's the full list, roughly in the order they show up on a printed or emailed invoice:

• Supplier name, address and GSTIN. This has to be the registered legal name and the address on your GST registration certificate, not a trade name that doesn't match your filings.
• A unique, sequential invoice number. Invoice numbers need to run in a consecutive series for a financial year, without gaps that can't be explained. Skipping numbers or reusing them is one of the first things a tax officer checks.
• Invoice date. This determines which tax period the sale falls into and when your GST liability kicks in.
• Recipient's name, address, and GSTIN if the buyer is GST-registered. Unregistered buyers still need a name and address, especially above a certain invoice value.
• HSN or SAC code. HSN for goods, SAC for services. How many digits you need depends on your annual turnover, more on that below.
• Description of goods or services, with quantity and unit where that applies.
• Taxable value, meaning the price before tax, after any discount is applied.
• Tax rate and tax amount, shown separately for CGST, SGST, or IGST, not bundled into one "GST" line.
• Place of supply, which matters most for inter-state sales, since it decides whether you charge IGST or CGST plus SGST.
• Whether tax is payable under reverse charge, if that applies to the transaction.
• Signature of the supplier or an authorised representative, which can be a digital signature on an electronic invoice.

How many digits does the HSN code need?

This is probably the question we hear most from small business owners. The digit requirement for HSN codes is tied to your turnover in the previous financial year, and the government has revised it more than once. Rather than quote a specific digit count here that might be outdated by the time you're reading this, check the current requirement for your turnover bracket on the GST portal or with your CA. What actually matters day to day is picking the correct HSN code for each product category and using it consistently across every invoice, credit note, and GST return you file.

Do very small businesses still need HSN codes?

Even businesses below the mandatory HSN threshold are usually better off including them anyway. It keeps your invoicing consistent if your turnover grows into a higher bracket mid-year, and plenty of buyers, larger companies especially, won't process your invoice for payment without one, regardless of what the strict legal minimum is for a business your size.

What about the CGST, SGST and IGST split specifically?

This is where paper-based or spreadsheet invoicing goes wrong most often. If the sale is within the same state, the tax splits into two equal halves, CGST and SGST. Cross a state line, or fall under one of the specific inter-state categories, and it's IGST at the full combined rate instead. Charge IGST on an intra-state sale, or the reverse, and that's a real compliance error, one that surfaces when your GSTIN gets reconciled against your buyer's input credit claim. We cover the mechanics of this in more detail in our explainer on CGST versus SGST versus IGST, but the short version is this: the invoice has to reflect the place of supply correctly, not just the price.

What's the difference between a tax invoice and a bill of supply?

If you're registered under the GST composition scheme, or you deal in exempt goods or services, you issue a bill of supply instead of a tax invoice. It looks similar on the surface, business name, address, GSTIN, invoice number, date, description, value, but it carries no tax amount, because no GST is being charged on that supply. Mixing the two up, printing a bill of supply that still shows a tax line, say, or issuing a full tax invoice when you're only eligible for a bill of supply, is worth checking with your CA if you're on the composition scheme.

How long do I need to keep copies of my invoices?

GST law requires businesses to retain invoices and related records for a specified period tied to your annual return filings, running into several years. You can find the underlying rules on record retention through the Central Board of Indirect Taxes and Customs, but because retention periods are exactly the kind of detail that gets updated by notification, keep this part simple: store every invoice, credit note, and debit note somewhere you can pull up instantly (digital beats paper here), and confirm the exact retention period for your business on the GST portal or with your CA rather than going by a number you half remember.

Does the invoice need to look a certain way visually?

GST law is prescriptive about content, not design. There's no mandated font, colour, or layout, which is why you'll see everything from plain black-and-white A4 printouts to branded PDF templates, all equally compliant, as long as the required fields are present and legible. What actually matters is that the information is unambiguous: a taxable value clearly separate from the tax amount, a tax split clearly labelled CGST/SGST or IGST rather than lumped together, and numbers that add up. Visual polish helps in practice, even though it isn't legally required, because a cleanly laid out invoice gets paid faster and questioned less.

What happens if an invoice is missing a mandatory field?

Two things, and neither is good. First, if your buyer is GST-registered, an incomplete invoice can delay or block their input tax credit claim, which gives them a reason to be annoyed with you specifically, not the tax system in general. Second, during your own GST audit or scrutiny, invoices missing fields like HSN codes or place of supply get flagged, and the same error repeated across many invoices tends to draw more attention than a single one-off slip. We've gone through the recurring patterns in more detail in our piece on common GST invoicing mistakes, and honestly, most of them come back to a handful of fields people forget to double-check.

None of this needs a lawyer to fix. It needs a consistent invoice format you don't have to rebuild from memory every time you bill someone.

A practical way to get this right every time

The businesses that stay compliant without much stress are usually the ones that stopped building invoices manually in Word or Excel and switched to a template or tool that already has every mandatory field baked in. If you'd rather not track this list by hand for every invoice, tools like Settle generate GST-compliant invoices with the CGST/SGST/IGST split calculated automatically based on the place of supply you enter, so you're not deciding tax logic invoice by invoice. It's free during early access at settle.markmydigi.com, and if speed is what you're after, we've also written up how to create a compliant invoice in under a minute once your basic setup is in place.

Whatever tool or template you end up using, the test is simple: could a tax officer, or your buyer's accountant, look at the invoice and find everything they need without calling you to ask? If yes, you're compliant. If they'd have to phone you for the HSN code or the GSTIN, fix the format before the next invoice goes out.

Frequently asked questions