GST Invoice Format: Mandatory Fields, E-Invoice Rules and Sample

A valid GST tax invoice in India must carry the specific particulars listed in Rule 46 of the CGST Rules, 2017: supplier and recipient details, a unique serial number, HSN or SAC codes, taxable value, tax rate and amount, place of supply and a signature. This guide walks through every mandatory field, explains when e-invoicing (IRN and QR code) applies, gives you a sample layout you can copy into Excel or your billing software, and lists the mistakes that most often cost small businesses their input tax credit or a notice from the department.

Why the invoice format matters more than you think

Under GST, the invoice is not just a request for payment. It is the document your buyer relies on to claim input tax credit, the record the department checks during an audit, and the source of every line in your GSTR-1. A missing GSTIN, a wrong place of supply or a duplicated invoice number can push your customer’s credit into a mismatch, and that usually ends with an awkward phone call asking you to issue a credit note and a fresh invoice.

For a small business, the cost of a bad invoice shows up in three places: delayed payments because the buyer’s accounts team rejects the bill, extra hours spent on amendments, and penalty exposure if the errors are systematic. Getting the template right once saves all three.

Mandatory fields on a GST tax invoice (Rule 46)

Rule 46 of the CGST Rules sets out the particulars every tax invoice issued by a registered person must contain. The full text of Rule 46 with its amendment history is worth bookmarking. In plain language, here is what your invoice needs.

Clause	Particular	Practical note
(a)	Supplier’s name, address and GSTIN	Use the address registered on the GST portal for that GSTIN.
(b)	Serial number	Up to 16 characters; letters, numbers, hyphen or slash; unique for the financial year.
(c)	Date of issue	Must fall within the time limit for issuing the invoice.
(d)	Recipient’s name, address and GSTIN or UIN	Required when the buyer is registered.
(e), (f)	Details of unregistered recipient	Name, address, delivery address and state name and code when taxable value is Rs 50,000 or more; below that, only if the buyer asks.
(g)	HSN code (goods) or SAC (services)	Number of digits depends on turnover (see below).
(h)	Description of goods or services	Be specific; “material” or “services” alone invites questions.
(i)	Quantity and unit (UQC)	For goods only, e.g. NOS, KGS, MTR.
(j), (k)	Total value and taxable value	Taxable value after discounts or abatement.
(l), (m)	Rate and amount of tax	Show CGST, SGST/UTGST, IGST and cess separately.
(n)	Place of supply with state name	Mandatory for inter-state supplies.
(o)	Delivery address	Only where it differs from place of supply.
(p)	Whether tax is payable on reverse charge	A simple “Reverse charge: Yes/No” line works.
(q)	Signature or digital signature	Not needed on an electronic invoice issued under the IT Act, 2000.
(r)	QR code with IRN	Only for e-invoices generated under Rule 48(4).
(s)	Declaration	Where a business above the e-invoice threshold is exempt from e-invoicing and issues a normal invoice.

HSN digits: 4 or 6?

Notification 78/2020-Central Tax, in force from 1 April 2021, ties the number of HSN digits to your aggregate turnover in the previous financial year:

• Turnover up to Rs 5 crore: 4-digit HSN on B2B invoices. On invoices to unregistered buyers (B2C), the HSN may be left out.
• Turnover above Rs 5 crore: 6-digit HSN on all tax invoices.

Many accounting packages let you store an 8-digit code anyway. That is fine, and 8 digits are needed for imports and exports, but make sure your GSTR-1 HSN summary matches what you print.

Invoice numbering that will not trip you up

The 16-character limit and “unique for a financial year” rule cause more trouble than any other field. A clean pattern is prefix-year-number, for example PNB/26-27/0001 (13 characters). Use separate series if you run multiple branches under one GSTIN, such as MUM/26-27/0001 and THN/26-27/0001. Restart numbering on 1 April each year, never reuse a cancelled number, and keep the same series for credit notes separate (for example CN/26-27/001).

When e-invoicing applies

E-invoicing does not change what goes on the invoice so much as how it is issued. You upload the invoice data (in the standard JSON schema) to an Invoice Registration Portal (IRP), which returns an Invoice Reference Number (IRN) and a signed QR code. That QR code must then be printed on the invoice.

The threshold has come down in stages from Rs 500 crore in 2020. Under Notification 10/2023-Central Tax, e-invoicing became mandatory from 1 August 2023 for businesses whose aggregate turnover exceeded Rs 5 crore in any financial year from 2017-18 onwards. Turnover is computed on the PAN, so all GSTINs under one PAN count together. Once you cross the limit, the obligation stays even if turnover dips later.

Your aggregate turnover (PAN level)	What applies
Up to Rs 5 crore in every year since 2017-18	Normal tax invoice; e-invoicing not mandatory.
Above Rs 5 crore in any year since 2017-18	E-invoice (IRN + QR code) for B2B invoices, credit notes, debit notes and exports.
Rs 10 crore or more	E-invoice must also be reported on the IRP within 30 days of the document date (since 1 April 2025).
Above Rs 500 crore	Dynamic QR code also required on B2C invoices (Notification 14/2020).

The 30-day rule came from a GSTN advisory of November 2024; Taxmann’s summary of the advisory explains that it covers invoices, credit notes and debit notes. If you are just above Rs 10 crore and your billing team batches uploads monthly, change that habit now: an invoice the IRP refuses is an invoice your buyer cannot claim credit on.

Some entities, such as banks, insurers, GTA operators and SEZ units, are exempted from e-invoicing. If you think you fall in an exempt class, confirm it with your consultant rather than assuming.

Sample GST invoice format (copy this layout)

Below is a plain layout that satisfies Rule 46 for a business under the e-invoicing threshold. The figures are illustrative.

Worked example: a digital marketing agency in Ahmedabad (Gujarat) bills a client in Bengaluru (Karnataka) for a month of social media management. Because the supplier and the place of supply are in different states, IGST applies. We assume an 18% rate for this example; always confirm the current rate for your SAC.

Section	What to print
Header	TAX INVOICE · Original for Recipient
Supplier block	Example Digital LLP, 3rd Floor, CG Road, Ahmedabad 380009, Gujarat (24) · GSTIN 24XXXXX0000X1ZX
Invoice details	Invoice No. AMD/26-27/0142 · Date 17-10-2026 · Reverse charge: No
Recipient block	Bill to: Example Foods Pvt Ltd, Indiranagar, Bengaluru 560038 · GSTIN 29XXXXX0000X1ZX · State: Karnataka (29)
Place of supply	Karnataka (29)
Line item	Social media management, September 2026 · SAC 998361 (confirm the right code for your service) · Qty 1 · Rate Rs 60,000
Taxable value	Rs 60,000
IGST @ 18%	Rs 10,800
Invoice total	Rs 70,800 (Rupees Seventy Thousand Eight Hundred only)
Footer	Bank details, payment terms, “Certified that the particulars given above are true and correct”, authorised signatory

If the same agency billed a client in Surat, the supply would be intra-state, and the Rs 10,800 would be split into CGST @ 9% (Rs 5,400) and SGST @ 9% (Rs 5,400). Getting this split wrong is a classic error: tax paid under the wrong head is not simply adjusted, and the refund-and-repay route takes time.

Copies you need to keep

Rule 48 asks for goods invoices in triplicate (original for the recipient, duplicate for the transporter, triplicate for the supplier) and services invoices in duplicate. Most businesses now print “Original for Recipient” and keep the rest digitally. Whether you print or store them digitally, keep your copies accessible for the full statutory retention period.

Time limits for issuing the invoice

• Goods: at or before the time of removal or delivery, under Section 31(1) of the CGST Act.
• Services: within 30 days of the date of supply (Rule 47). Banks, insurers and NBFCs get 45 days.
• Continuous supply: on or before the due date of payment, or as per the contract milestones.
• Advance received: issue a receipt voucher; the tax invoice follows when the supply happens.

Back-dating invoices to fit a month is a habit to drop. With e-invoicing timestamps and the 30-day IRP rule, back-dating is both visible and risky.

Tax invoice, bill of supply, or something else?

Not every document you raise is a tax invoice. Using the wrong one is a frequent mistake for businesses that have just moved from composition to regular registration, or the other way round.

Document	Who issues it	Tax shown?
Tax invoice	Regular taxpayer making a taxable supply	Yes
Bill of supply	Composition dealer, or anyone supplying exempt goods/services	No
Receipt voucher	On receiving an advance	Tax on advance, where applicable
Credit note / debit note	To reduce or increase value or tax after the invoice	Yes, linked to original invoice
Delivery challan	Movement without sale (job work, approval basis)	No
Self-invoice	Recipient paying tax under reverse charge on purchases from unregistered suppliers	Yes

Ten common GST invoice mistakes (and the fix)

1. Wrong or outdated buyer GSTIN. Validate the GSTIN on the GST portal before saving a new customer. A typo makes the invoice invisible in the buyer’s GSTR-2B.
2. Place of supply left blank on inter-state bills. Clause (n) is mandatory; the place of supply decides IGST vs CGST plus SGST.
3. Duplicate invoice numbers across branches. Use a branch prefix or separate series.
4. Numbers longer than 16 characters. Long prefixes like EXAMPLEDIGITAL/2026-2027/00001 fail validation.
5. Charging CGST and SGST on an inter-state sale. Check the state code in the buyer’s GSTIN (the first two digits) against your own.
6. Missing HSN or wrong number of digits. Match the digits to your previous year’s turnover.
7. Vague descriptions. “Professional charges” is weaker than “Website maintenance, October 2026”.
8. Ignoring the Rs 50,000 rule for unregistered buyers. Above that taxable value, capture the buyer’s name, address and state.
9. Raising a fresh invoice instead of a credit note. Price corrections after issue should go through a credit or debit note referencing the original.
10. Uploading e-invoices late. If your turnover is Rs 10 crore or more, set a weekly IRP upload routine.

A quick pre-send checklist

Pin this beside your billing desk or add it as a validation step in your software:

• Supplier GSTIN and address match the registration certificate.
• Invoice number is unique, sequential and 16 characters or fewer.
• Buyer GSTIN verified; state code matches place of supply.
• Correct tax head: IGST for inter-state, CGST plus SGST for intra-state.
• HSN/SAC present with the right number of digits.
• Taxable value, rate, tax amount and total add up; amount in words matches.
• Reverse charge line present.
• IRN and QR code printed if you are on e-invoicing.
• Signature or digital signature (or electronic issue under the IT Act).

If you send a press release or a client announcement alongside a large launch order, keep invoicing separate from marketing paperwork; the buyer’s accounts team only wants the invoice.

Frequently Asked Questions

Is a handwritten GST invoice valid?

Yes, a handwritten invoice is valid if it carries all Rule 46 particulars and is signed. In practice, most businesses use software because GSTR-1 data then comes from the same source. Businesses on e-invoicing cannot issue a B2B invoice without generating an IRN, so handwritten bills do not work for them.

Do I need a signature on a GST invoice I email as a PDF?

Rule 46 says a signature or digital signature is not required for an electronic invoice issued under the Information Technology Act, 2000. Many businesses still add a scanned or digital signature because buyers’ accounts teams prefer it.

What is the e-invoice limit for 2026?

The threshold remains Rs 5 crore of aggregate turnover in any financial year from 2017-18 onwards, in force since 1 August 2023. We found no notification lowering it further as of October 2026, but check the CBIC and GST portals for updates.

Can my invoice number restart every month?

No. The number must be unique for the financial year, so a series that restarts monthly will create duplicates. Restart only on 1 April.

What happens if my buyer’s GSTIN is wrong on an invoice I already filed in GSTR-1?

You can amend the invoice details in a later GSTR-1 within the permitted time, which moves the credit to the correct GSTIN. Do it quickly, because your buyer’s credit depends on it.

Does a composition dealer show GST on the bill?

No. A composition taxpayer issues a bill of supply and cannot collect tax from the buyer. The words “composition taxable person, not eligible to collect tax on supplies” should appear on the bill.

Set up the template once, then audit monthly

The fastest win is to build one master template that covers every Rule 46 field, lock the numbering format, and validate GSTINs at the time of customer creation. Then spend fifteen minutes each month comparing your GSTR-1 with your sales register. GST rules and notifications change, so confirm the current position on the official CBIC and GST portals or with your chartered accountant before you rely on any threshold mentioned here.