GST Invoicing — Tax Invoice Rules
A GST invoice (or GST tax invoice) is the primary commercial document in the GST system. It is the document on which the supplier declares the details of the supply — the goods or services supplied, the taxable value, the applicable GST rate, and the GST amounts (CGST, SGST/UTGST, or IGST) — and on the basis of which the recipient claims Input Tax Credit (ITC). GST invoicing rules under Section 31 of the CGST Act, 2017 and Rule 46 of the CGST Rules, 2017 prescribe the mandatory fields that every GST tax invoice must contain, the time limit within which it must be issued, and the number of copies required. Getting GST invoicing right is not just a commercial practice — it is a legal compliance requirement. An incorrect GST invoice (missing mandatory fields, wrong GSTIN, incorrect HSN code, or wrong tax rate) can result in the recipient being denied ITC, attract GST penalties, and in serious cases trigger GST notices or assessment proceedings.
N D Savla & Associates, Chartered Accountants in Mumbai, provides GST invoicing advisory: reviewing invoice formats, identifying non-compliant invoicing practices, advising on the correct GST treatment for specific transactions, and implementing corrective measures where past GST invoicing has been deficient. This guide covers the mandatory fields for a valid GST tax invoice, the time limit for issuing one, the types of GST documents, credit notes and debit notes, the difference between B2B and B2C invoices, HSN/SAC code requirements, and specific rules for service providers. For the e-invoicing requirement (mandatory for B2B invoices above Rs. 5 crore turnover), see our GST E-Invoicing Software guide.
Mandatory Fields in a GST Tax Invoice
Rule 46 of the CGST Rules, 2017 specifies that every GST tax invoice issued by a registered supplier must contain the following fields:
| Mandatory GST Invoice Field | Details / Requirements |
|---|
| Name, address, and GSTIN of the supplier | The GSTIN of the supplier must be as per the GST certificate for the place of supply state |
| Consecutive serial number | Unique, consecutive invoice number for the financial year. May contain alphabets, numbers, and/or hyphen, not exceeding 16 characters. Can be a different series per branch or financial year |
| Date of issue | Date of supply (for goods) or date of invoice (for services) |
| Name, address, and GSTIN of the recipient (for B2B) | GSTIN must be stated for all B2B invoices so the recipient can claim ITC. For B2C (unregistered buyer), name and address are sufficient |
| HSN code (for goods) or SAC code (for services) | Turnover up to Rs. 5 crore: 4-digit HSN. Above Rs. 5 crore: 6-digit HSN. Exports and specific goods: 8-digit. SAC codes for services are 6 digits |
| Description of goods or services | Must be sufficient to identify the nature of the supply |
| Quantity and unit of measurement (for goods) | Physical quantity (kg, litres, metres, pieces, numbers, etc.) and the corresponding unit |
| Taxable value of goods or services | The value on which GST is computed, after adjusting discounts known at the time of supply. Post-supply discounts must be reflected in a credit note |
| GST rate and GST amount | Rate: 5%, 12%, 18%, or 28% (or 0.25%/3% for specific goods). Amount: CGST + SGST for intra-state supplies; full IGST for inter-state |
| Place of supply | State name and code, which determines whether CGST+SGST or IGST applies |
| Signature or digital signature | Manual or digital signature of the authorised signatory. For e-invoices: the IRP-generated digital signature on the JSON serves as the signature |
Time Limit for Issuing a GST Invoice
- Supply of goods: must be issued at the time of removal of goods (for goods moved by the supplier) or at the time of delivery. In practice, most goods invoices are raised at the time of dispatch
- Supply of services: must be issued within 30 days from the date of supply. For banking companies, financial institutions, and NBFCs: within 45 days
- Continuous supply of services (e.g. subscriptions, AMC): must be issued on or before the due date for payment specified in the contract, or upon receipt of each payment, or at the end of each period for which payment is made — whichever is earlier
- Advance received: a Receipt Voucher (not a full GST invoice) must be issued for the advance. The GST invoice is raised when the supply is made
Types of GST Documents — When to Use What
- GST Tax Invoice: used for all taxable supplies made by a regular registered taxpayer
- Bill of Supply: used instead of a tax invoice when the supply is exempt from GST or the supplier is a composition scheme taxpayer. Shows no GST amount; carries the "Composition Taxable Person, not eligible to collect tax" legend
- Delivery Challan: used for movement of goods that is not a supply (job work, exhibition, samples without consideration, goods returned). Not a GST invoice and does not carry GST
- Receipt Voucher: issued when an advance is received before the supply is made, showing the advance amount and applicable GST
- Payment Voucher: issued by the recipient when paying GST on a Reverse Charge Mechanism (RCM) supply from an unregistered supplier
- Refund Voucher: issued when an advance received (for which a Receipt Voucher was issued) is later returned because the supply was not made
GST Credit Note and Debit Note
Credit Note
A GST credit note is issued by the supplier to the recipient when the original invoice value was higher than the actual supply value (goods returned, supply not made in full, post-supply discount) or the GST rate/taxable value was wrong (excess GST charged). It reduces the supplier's GST liability for the period issued and reduces the recipient's ITC to the extent already claimed.
Debit Note
A GST debit note is issued when the original invoice value was lower than the actual supply value (additional goods supplied, price increase) or additional GST needs to be charged. It increases the supplier's GST liability and entitles the recipient to additional ITC.
B2B vs B2C GST Invoice Differences
- B2B invoice (to a registered business): must contain the recipient's GSTIN, full taxable value and GST breakup, and must be reported in GSTR-1 with GSTIN details for the recipient's GSTR-2B. Businesses above Rs. 5 crore must also carry IRN and QR code (e-invoicing)
- B2C invoice (to an unregistered consumer): no recipient GSTIN needed; state-wise summary is sufficient in GSTR-1 for supplies above Rs. 2.5 lakh; no ITC claim by recipient. For B2C sales above Rs. 2.5 lakh, individual invoice details must be reported state-wise
- B2C QR code: businesses with turnover above Rs. 500 crore must display a dynamic QR code on B2C invoices — a separate requirement from the e-invoicing IRN for B2B
Frequently Asked Questions — GST Invoicing
Our service invoice is raised 40 days after the service was provided. Is this non-compliant?
Yes. For supply of services, the GST invoice must be issued within 30 days from the date of supply (45 days for banking companies and NBFCs). A 40-day invoice is late by 10 days — a GST invoicing violation under Section 31 read with Rule 47. While minor delays may not be actively pursued, they can create problems during audit or assessment, including questions on the recipient's ITC eligibility for the period of delay.
We issued a GST invoice with the wrong HSN code. How do we correct it?
An incorrect HSN code can be corrected by issuing a revised GST invoice (if within the same period and not already reported in GSTR-1) or by issuing a debit note/credit note to correct any value impact. If the taxable value and GST amount are correct, the HSN change may be addressed through a GSTR-1 amendment. Systematic incorrect HSN coding across many invoices can create significant GST demand and ITC reversal issues for both supplier and recipient.
Can we issue a single GST invoice for multiple deliveries to the same customer in a month?
Yes, but with limitations. For a continuous supply of goods or services where a contract specifies periodic deliveries and billing, a consolidated invoice for the period can be issued. For individual, separate supplies, separate invoices are technically required — though a periodic consolidated invoice is common and acceptable in practice for continuous supply situations. Ensure it clearly identifies the period covered and deliveries included.