GST Invoice Format — All Mandatory Fields and Rules
A GST invoice is not just a payment request — it is a legal document. Moreover, it is the only instrument through which your buyer can claim Input Tax Credit. Furthermore, an invoice missing even one mandatory field can be considered invalid under the GST Act — resulting in rejected ITC claims, penalties, and supplier disputes.
- Every GST tax invoice must contain 16 mandatory fields under Rule 46 of the CGST Rules, 2017.
- There are 4 invoice types: Tax Invoice, Bill of Supply, Credit Note, and Debit Note — issued depending on registration status and transaction.
- E-invoicing is mandatory above ₹5 crore turnover, with a 30-day IRP upload window for businesses above ₹10 crore.
- Missing the IRN/QR code on an eligible e-invoice makes it legally invalid, regardless of other fields being correct.
- The most common invoice mistakes — wrong GSTIN, wrong place of supply, non-sequential numbering — directly block the buyer's ITC claim.
What Is a GST Invoice?
A GST invoice is a legal document issued by a registered supplier for the sale of taxable goods or services, recording the value, applicable GST rate, and tax amount. Unlike a simple bill, it is the only document through which a GST-registered buyer can claim Input Tax Credit (ITC) — so its format is governed by strict statutory rules, not business preference.
Getting the invoice format right is therefore not merely an administrative detail. Specifically, it is the foundation of your entire GST compliance. Additionally, with e-invoicing now mandatory for businesses above ₹5 crore, the stakes of non-compliance have increased significantly.
What Are the 16 Mandatory Fields on a GST Invoice?
Rule 46 of the CGST Rules prescribes the exact fields every tax invoice must contain. Moreover, these apply to all GST-registered businesses issuing invoices for taxable supplies. Consequently, whether you use a manual template, Excel, or invoicing software, every invoice must include all 16 elements.
Your complete legal name as registered, registered address, and 15-digit GSTIN. Furthermore, the state code embedded in your GSTIN determines whether CGST/SGST or IGST applies.
A unique consecutive serial number within a financial year. Specifically, it can contain up to 16 characters including letters, numbers, and / or - symbols. Moreover, gaps in numbering are not permitted.
The date of issue. Furthermore, for goods, the invoice must be issued before or at the time of delivery. For services, it must be issued within 30 days of supply.
If the buyer is GST-registered, their GSTIN is mandatory. Consequently, an incorrect GSTIN — even one digit wrong — prevents the buyer from claiming ITC.
The state where the supply is deemed to occur. Specifically, this field determines whether CGST+SGST or IGST applies — it is not simply the delivery address.
The classification code for goods (Harmonised System of Nomenclature) or services (Service Accounting Code). Moreover, businesses above ₹5 crore must show the full 8-digit code.
A clear description of what was supplied. Furthermore, vague descriptions like "services rendered" are insufficient and may trigger audit queries.
Quantity in the relevant unit of measurement (kg, metres, pieces, etc.). Additionally, this field enables buyers and auditors to verify transaction values against market rates.
The value of goods or services before GST — also called the GST-exclusive amount. Consequently, this is the base on which the tax percentage is applied.
The applicable rate — 5%, 12%, 18%, or 28%. Furthermore, if multiple items attract different rates, each must be listed separately with its own tax line.
The actual tax amounts in rupees — either split as CGST/SGST for intra-state or shown as IGST for inter-state. Moreover, these amounts must be mathematically consistent with the rate and taxable value.
Taxable value plus all applicable GST. Additionally, if the invoice is in foreign currency, the INR equivalent must also be stated.
A mandatory Yes/No statement. Furthermore, if RCM applies, the recipient pays GST — not the supplier. Consequently, this field alerts the buyer to their liability.
Physical or digital signature of the supplier or their authorised representative. Moreover, e-invoices authenticated through the IRP system are deemed digitally signed.
Required when goods are shipped to a location different from the billing address. Specifically, this determines the correct state for IGST/SGST classification.
Additional recipient details — name, address, and state of delivery — are mandatory when selling to an unregistered person and the invoice value exceeds ₹50,000.
What Types of GST Invoices Are There?
Not every transaction requires a tax invoice. Specifically, the type of invoice depends on your GST registration status, the nature of the supply, and whether the recipient can claim ITC.
Is E-Invoicing Mandatory for Your Business?
E-invoicing under GST requires eligible businesses to register invoices on the Invoice Registration Portal (IRP) before sending them to buyers. Moreover, the IRP generates a unique Invoice Reference Number (IRN) and a QR code that must appear on the invoice.
Currently, e-invoicing is mandatory for businesses with annual aggregate turnover above ₹5 crore. Furthermore, from 1 April 2025, businesses above ₹10 crore must upload invoices to the IRP within 30 days of the invoice date — invoices uploaded later are rejected. Additionally, e-invoices are automatically populated in GSTR-1, significantly reducing manual filing effort. Consequently, businesses close to the ₹5 crore threshold should prepare their systems proactively rather than scrambling at the last moment.
Official e-invoice portal (NIC IRP)
What happens if you don't generate an e-invoice when required?
The consequences are significant. Specifically, a non-e-invoiced invoice from an eligible business is treated as invalid under GST law. Moreover, your buyer cannot claim ITC against it — creating a serious commercial dispute. Furthermore, you face a penalty of ₹10,000 per invoice or 100% of the tax involved, whichever is higher. As a result, e-invoicing compliance is not a back-office detail — it directly affects your business relationships.
Issue the invoice in your normal billing or accounting software as usual.
Upload the invoice details (JSON) to the Invoice Registration Portal (IRP) within 30 days of the invoice date.
The IRP validates the data and returns a unique Invoice Reference Number (IRN) and a signed QR code.
Print the IRN and QR code on the invoice copy you send to the buyer — without these, the e-invoice is not valid.
The validated data auto-flows into your GSTR-1, reducing manual return-filing effort.
What Are the Most Common GST Invoice Mistakes to Avoid?
Wrong GSTIN: A single digit error in the buyer's GSTIN invalidates their ITC claim. Furthermore, always verify GSTINs on the official GST portal before issuing an invoice.
Incorrect HSN/SAC code: Using a wrong code misclassifies the supply and may trigger audit questions. Additionally, it may indicate an incorrect GST rate was applied.
Wrong place of supply: Charging CGST/SGST on an inter-state transaction — or IGST on an intra-state one — creates a liability mismatch that is extremely difficult to correct after filing.
Non-sequential invoice numbers: Gaps in invoice numbering are a red flag in GST audits. Consequently, every invoice number in a financial year must follow without interruption.
Omitting RCM declaration: Failing to state whether reverse charge applies leaves the buyer uncertain about their tax liability. Moreover, it may result in double tax payment.
Missing IRN/QR code for eligible businesses: If you are above the e-invoicing threshold and omit the IRN, your invoice is legally invalid — regardless of how correct all other fields are.
To calculate the exact CGST, SGST, and IGST amounts that must appear on your invoice, use our free GST calculator. Additionally, for understanding which type of GST applies to your transaction, read our guide on CGST vs SGST vs IGST. Furthermore, to understand how your buyer uses this invoice to claim credit, see our article on Input Tax Credit under GST.
CBIC — CGST Rules, 2017 (Rule 46)
GST Invoice — Frequently Asked Questions
Is a digital signature mandatory on a GST invoice?
Yes, unless the invoice is an e-invoice authenticated through the IRP — those are deemed digitally signed automatically. Manually issued invoices still need a physical or digital signature of the authorised signatory.
Can an invoice number be reused across financial years?
Yes. Invoice numbering must be unique and sequential within a single financial year, but the series can reset at the start of a new financial year.
What is the penalty for not issuing an e-invoice when required?
₹10,000 per invoice or 100% of the tax involved, whichever is higher — and the buyer cannot claim ITC against a non-compliant invoice.
Is a Bill of Supply the same as a Tax Invoice?
No. A Bill of Supply is issued for exempt goods/services or by composition scheme dealers, and unlike a Tax Invoice, it does not show any GST amount because no tax is charged.
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