Ask ten business owners what a "GST invoice format" requires and you will likely get ten different half-right answers. There is no single government-prescribed template file you must download and fill in, but GST law does specify a defined list of fields that a tax invoice must contain to be considered valid. Missing even one mandatory field can turn a perfectly normal-looking invoice into one your buyer cannot use to claim input tax credit. This guide sets out the GST invoice format field list in full, flags which fields are conditional, and explains how the format shifts for exports and consumer-facing sales.
Format is flexible, content is not
GST rules do not mandate a specific visual layout, font, or software. What they mandate is the presence of certain data points on the document, in a legible form, whether it is a printed invoice or a PDF generated by software. This is why two businesses in the same industry can have invoices that look completely different and both be fully compliant, or look identical and both be missing a required field. A useful way to think about it: treat the field list below as the non-negotiable content, and treat everything else about how the invoice looks, colour, logo placement, paper size, as a design decision that has no bearing on whether the document is valid.
Mandatory fields on every tax invoice
| Field | What it covers | Example |
|---|---|---|
| Invoice number and date | A consecutive, unique series for the financial year | INV-2026-00147, dated 12-08-2026 |
| Supplier details | Legal name, address, and GSTIN of the seller | Ravi Traders, Pune, GSTIN 27ABCDE1234F1Z5 |
| Buyer details | Name, address, and GSTIN (if the buyer is registered) | Nashik Retail Hub, GSTIN 27XXXXX... |
| Place of supply | State where the supply is deemed to occur, for tax type | Maharashtra |
| HSN/SAC code | Classification code for each item, at the required digit length | 8544 (electrical wiring) |
| Description of goods/services | Clear item description matching the HSN | PVC insulated copper wire |
| Quantity and unit | Number of units and unit of measure, for goods | 500 metres |
| Taxable value | Value before tax, per item and in total | ₹25,000 |
| Tax rate and type | Applicable GST rate, split as CGST/SGST or IGST | 18% (9% CGST + 9% SGST) |
| Tax amount | Computed tax for each type, shown separately | ₹2,250 + ₹2,250 |
| Total invoice value | Sum of taxable value and tax, usually rounded | ₹29,500 |
| Signature | Of the supplier or an authorised signatory, physical or digital | Authorised signatory name/stamp |
Fields that apply only in specific situations
- Reverse charge declaration - required when the recipient, not the supplier, is liable to pay tax on the supply.
- Shipping address - needed separately from the billing address when goods are delivered to a different location.
- Export or SEZ endorsement - a statement such as supply meant for export or to an SEZ unit, with or without payment of integrated tax, along with shipping bill or LUT references where relevant.
- Delivery challan cross-reference - relevant when goods have already moved under a delivery challan and the tax invoice follows later.
- Recipient's state code - specifically for inter-state supplies, to establish the correct place of supply.
How the format shifts by invoice type
| Invoice type | Key format difference |
|---|---|
| B2B (registered buyer) | Buyer's GSTIN is mandatory; feeds directly into the buyer's GSTR-2B |
| B2C large (high-value inter-state) | Buyer GSTIN not required, but place of supply and buyer address still matter for reporting thresholds |
| B2C small | Simplified buyer details; consolidated reporting is generally allowed for GSTR-1 purposes |
| Export | Requires the export/SEZ declaration, and typically shows value in the invoice currency alongside INR equivalent |
A quick self-check before you send an invoice out
- Does the invoice number continue the series without a gap or repeat?
- Is the buyer's GSTIN present and does it match their registered name?
- Is the place of supply shown, and does it match whether you charged CGST+SGST or IGST?
- Does every line item carry an HSN/SAC code at the correct digit length for your turnover?
- Do the taxable value, tax amount, and total add up without rounding surprises?
Why the field list matters beyond avoiding penalties
It is tempting to treat the mandatory field list as a compliance checkbox, but each field does practical work. The invoice number and date establish which return period the transaction belongs to. The buyer's GSTIN is what lets the transaction appear correctly in their GSTR-2B. The place of supply decides which government, central or state, the tax is credited to, and getting it wrong (charging CGST+SGST instead of IGST, or the reverse) is one of the more disruptive errors to unwind after the fact, since it usually means reversing and reissuing the tax entirely rather than a simple correction.
Formatting choices that are not compliance issues, but cause confusion anyway
Some things businesses worry about are not actually mandatory, but still cause friction if handled inconsistently:
- Invoice language. There is no requirement to issue invoices only in English, but keeping a consistent language across your invoice series avoids confusion for buyers and your own accounting team.
- Logo and branding placement. Purely a business choice, with no bearing on GST validity, as long as the mandatory fields are present and legible.
- Currency display for domestic sales. Domestic invoices should be in INR; foreign currency display alongside INR is relevant mainly for export invoices.
- PDF versus printed paper. Both are acceptable; what matters is that the record is retained and reproducible for as long as required.
Keeping the format consistent without re-checking every invoice
Once the field list is built into your invoicing template, the format stops being something you think about per invoice. OneBooks GST's accounting software generates invoice PDFs that carry these fields consistently, so numbering, HSN, and tax splits do not drift from one invoice to the next, and the same data flows into GSTR-1 automation for your monthly filing. If you want the field list applied to a real invoice step by step, see our guide on how to create a GST-compliant invoice; for the distinction between when you need a full tax invoice versus a simpler document, see tax invoice vs bill of supply. You can also cross-check your GST rate assumptions with the GST calculator.
A Worked Example: Same Sale, Two Tax Treatments
Take a seller in Maharashtra who ships 500 metres of PVC insulated copper wire at ₹50 per metre, a taxable value of ₹25,000, taxed at 18%. If the buyer is also in Maharashtra, the invoice splits the tax as CGST 9% (₹2,250) and SGST 9% (₹2,250), for a total invoice value of ₹29,500. If the same order ships instead to a buyer in Karnataka, the supply becomes inter-state, and the full 18% is charged as IGST (₹4,500) rather than split — the taxable value and total stay the same, but the tax-type fields change completely. Getting the place-of-supply field wrong here, charging CGST+SGST for what is actually an inter-state sale, is one of the more disruptive invoice errors, since unwinding it means reversing the wrongly charged tax type and reissuing the correct one rather than editing a single number.
Sector-Specific Notes
- Service invoices carry a SAC code instead of HSN, and typically have no meaningful "quantity" field — value is usually billed against the service description and period covered rather than units.
- E-commerce sellers. On some marketplaces the platform issues the customer-facing invoice on the seller's behalf, but the underlying tax data (GSTIN, HSN, tax split) still needs to reconcile with what the seller reports in GSTR-1, so sellers should keep their own record of what was actually charged rather than relying solely on the marketplace's copy.
- Export invoices. Beyond the SEZ/export endorsement, exporters typically choose between shipping under a Letter of Undertaking (LUT) without paying IGST, or paying IGST and claiming a refund later; the declaration wording on the invoice differs by route, so confirm the correct text for whichever route applies to you.
Edge Case: Small-Value and Consolidated Sales
For low-value sales to unregistered (B2C) buyers, GST provisions generally allow a simplified or consolidated tax invoice below a certain per-transaction value where the buyer has not asked for a full invoice, rather than requiring a full-format invoice for every small cash sale. This threshold has changed in the past, so verify the current value on the GST portal before relying on it, and note that a buyer who explicitly requests a proper tax invoice is entitled to one regardless of the sale value.
Frequently asked questions
Is there an official GST invoice template I must use?
No single mandatory template exists. You can design your own layout, printed or digital, as long as it contains all the fields GST law requires for that type of supply.
Is buyer GSTIN mandatory on every invoice?
Only when the buyer is GST-registered. For unregistered consumer sales (B2C), GSTIN is not applicable, though other fields like place of supply still matter.
How many digits of HSN code are required?
The required digit length depends on your aggregate turnover, and the thresholds have changed over time, so confirm the current requirement on the GST portal rather than assuming a fixed number of digits.
What happens if I forget to show tax type as CGST/SGST or IGST separately?
The invoice may still be usable, but a missing or wrong tax-type split creates confusion for the buyer's credit claim and can cause the invoice to be flagged during reconciliation.
Do digital invoices need a physical signature?
A digital or electronic signature meeting applicable authentication requirements is generally acceptable in place of a physical signature for software-generated invoices.
Can I skip a full invoice for very small cash sales?
GST provisions generally allow a simplified or consolidated tax invoice for low-value unregistered sales where the buyer does not request a full invoice, though the exact value threshold has changed over time and should be verified on the GST portal. A buyer who asks for a full tax invoice is entitled to receive one regardless of the sale value.
Automating the repetitive parts with OneBooks GST
Where this becomes repetitive month after month, OneBooks GST keeps invoice entry and return preparation on the same data, so an invoice raised in the month appears correctly in the return.
Keeping the original source file, the reviewed working copy and the final export together is what makes the same check repeatable next period, and OneBooks GST stores them against the filing period.
