Under GST, an invoice is much more than a request for payment. It's the legal record of a sale, the document your customer relies on to claim input tax credit (ITC), and one of the first things an officer checks during an audit.
A missing GSTIN, a wrong tax type, or a gap in your invoice numbers may look minor. But it can hold up your customer's ITC, lead to mismatches in your returns, and in some cases attract penalties.
This guide covers the GST invoicing rules every Indian business should know: which document to issue, what it must contain, how to number it, when to issue it and how e-invoicing, credit notes and debit notes fit in.
Every business registered under GST must issue a proper GST document for each taxable supply of goods or services. Which document you issue depends on what you're supplying and how you're registered.
| Document | When to use it |
|---|---|
| Tax invoice | A registered business making a taxable supply of goods or services |
| Bill of supply | Supplying exempt goods or services, or when you're registered under the composition scheme |
| Receipt voucher | Receiving an advance payment before the supply takes place |
| Refund voucher | Refunding an advance when the supply doesn't happen |
| Credit note | Reducing the value or tax of an invoice already issued, such as for returns, discounts, or overcharging |
| Debit note | Increasing the value or tax of an invoice already issued, such as for undercharging |
| Delivery challan | Moving goods without a sale, such as for job work, approval, or supply of liquid gas |
For most businesses, the tax invoice is the everyday document. The rest of this guide focuses mainly on it.
A GST tax invoice must include the following details:
| Section | Required details |
|---|---|
| Supplier details | Legal name, address, and GSTIN |
| Invoice details | A unique, consecutive invoice number for the financial year, and the invoice date |
| Customer details | Name, address, and GSTIN if the customer is registered. For unregistered customers, name and address are required above a set invoice value, and the state is needed to determine place of supply |
| Supply details | Description of goods or services, HSN or SAC code, quantity and unit (for goods) |
| Value | Total value, any discount and the taxable value |
| Tax | Tax rate and amount, shown separately for CGST and SGST, or IGST, plus any cess |
| Place of supply | State name and code, especially for inter-state supplies |
| Delivery address | If different from the billing address |
| Reverse charge | Whether tax is payable on reverse charge |
| Authorisation | Signature or digital signature of the supplier or an authorised person |
Missing even one of these can cause trouble for your customer when they claim ITC. Use a standard template so every invoice includes every field, every time.
Invoice numbers under GST must follow a few simple rules:
A common format combines a prefix, the financial year, and a running number, for example `INV/26-27/0001`. Many businesses restart the running number at the start of each financial year.
You'll also report the invoice number ranges you've used in your GST returns, so a clean, predictable series saves time at filing.
HSN (Harmonised System of Nomenclature) codes classify goods. SAC (Services Accounting Code) codes classify services. The number of digits you must show depends on your aggregate annual turnover in the previous financial year.
| Aggregate annual turnover | Digits required on invoices |
|---|---|
| Up to ₹5 crore | 4-digit HSN/SAC code for B2B invoices |
| Above ₹5 crore | 6-digit HSN/SAC code for all invoices |
Using the right code matters because it also decides the GST rate. A wrong code can mean the wrong tax, which leads to short payment, excess payment, or a notice. Save the correct code against each product or service in your billing system so it's applied automatically.
Which tax you charge depends on the place of supply, not simply where your customer's office is.
| Type of supply | Tax charged | Example at 18% on ₹10,000 |
|---|---|---|
| Intra-state (supplier and place of supply in the same state) | CGST + SGST | CGST ₹900 + SGST ₹900 |
| Inter-state (supplier and place of supply in different states) | IGST | IGST ₹1,800 |
| Exports and supplies to SEZs | IGST (or zero-rated under LUT) | IGST ₹1,800, or nil under LUT |
For goods, the place of supply is usually where the goods are delivered. For most services to a registered business, it's the customer's registered location. Some services, like those tied to property, events, or transport, have special rules.
Charging CGST and SGST when you should have charged IGST (or the other way round) is one of the most common GST errors. Correcting it isn't just a matter of paying the difference; the wrongly paid tax has to be claimed back as a refund. Setting up the customer's state correctly in your billing system prevents this.
GST sets time limits for issuing invoices. Issuing late can affect when tax becomes payable and create mismatches in your returns.
| Type of supply | When to issue the invoice |
|---|---|
| Goods | At or before the time the goods are removed or delivered |
| Continuous supply of goods | On or before the date each statement is issued or each payment is received |
| Services | Within 30 days of the date of supply |
| Services by banks, NBFCs, and insurance companies | Within 45 days of the date of supply |
| Continuous supply of services (with a due date) | On or before the payment due date |
Number of copies:
Digital copies are acceptable, as long as you store them securely and can produce them when asked.
E-invoicing doesn't mean emailing a PDF. It means registering each B2B invoice on the government's Invoice Registration Portal (IRP), which validates it and returns a unique Invoice Reference Number (IRN) and a signed QR code.
Who needs to generate e-invoices? Businesses whose aggregate annual turnover has crossed ₹5 crore in any financial year since 2017–18 must generate e-invoices. Some sectors, such as banks, insurance companies, and passenger transport services, are exempt.
Which documents are covered? B2B tax invoices, exports, and credit and debit notes issued to registered businesses. B2C invoices are generally not reported to the IRP.
What changes on the invoice? An e-invoice carries the IRN and QR code from the IRP. An invoice that should have been an e-invoice but wasn't registered is not treated as a valid invoice, and your customer may not be able to claim ITC on it.
Reporting deadline: Businesses with an aggregate turnover of ₹10 crore or more must report invoices to the IRP within 30 days of the invoice date. After that, the portal won't accept them.
Automatic return filing: Details from registered e-invoices flow into your GSTR-1 and the e-way bill system, which reduces manual data entry.
Thresholds and timelines have changed several times since e-invoicing began, so check the latest notifications on the GST portal.
Once issued, a GST invoice shouldn't be edited or deleted. Any change in value or tax is made through a separate document linked to the original invoice.
| Document | Use it when | Effect |
|---|---|---|
| Credit note | Goods are returned, a post-sale discount is given, services are deficient or you overcharged | Reduces the taxable value and tax |
| Debit note | You undercharged the value or tax on the original invoice | Increases the taxable value and tax |
| Revised invoice | Issued for supplies made between the effective date of registration and the date the registration certificate was granted | Replaces invoices issued before your GSTIN was available |
Keep these rules in mind:
Most of these mistakes come from manual work. A billing system that stores customer, product and tax details once and applies them automatically removes most of the risk.
Mocha QuickBill is built for Indian businesses, with GST rules built into every invoice it creates.
With QuickBill, GST compliance becomes part of how you bill, not a separate task at month-end.
GST invoicing comes down to a handful of rules: issue the right document, include every mandatory field, number invoices consistently, apply the correct tax type, issue on time, and correct mistakes through credit or debit notes. For larger businesses, add e-invoicing to that list.
Get these right, and your customers can claim ITC without delays, your returns match your books and audits become far less stressful.
GST rules are updated from time to time, so review your process with your CA regularly and keep an eye on notifications from the GST Council and the GST portal.
Want every invoice to be GST-compliant by default? Try Mocha QuickBill free and create your first GST-ready invoice in minutes.
A signature or digital signature of the supplier or an authorised person is required on a tax invoice. E-invoices registered on the IRP carry a digital signature from the portal.
Yes, if the customer isn't registered. It's then a B2C invoice, and the customer can't claim ITC on it.
For supplies under ₹200 to unregistered customers who don't ask for an invoice, you can issue one consolidated invoice for all such sales at the end of the day.
You shouldn't delete an issued invoice. If a supply didn't happen, issue a credit note or mark the invoice as cancelled and keep it on record. E-invoices can be cancelled on the IRP within 24 hours of generation.
Yes. Each series must be unique and consecutive within the financial year.
Correct it with a credit note or debit note linked to the original invoice, rather than editing it.