What a Valid GST Invoice Must Contain: A Practical Checklist for India

If your business is registered under GST, every taxable sale needs a proper tax invoice. A clean invoice is not just paperwork: your customer needs it to claim input tax credit, and it is your main proof of sale if the tax department ever asks questions. This guide walks through what a GST invoice normally has to carry, based on the rules most small businesses deal with day to day.

The core details on every tax invoice

• Supplier details: your business name, address and GSTIN.
• Invoice number: a unique, consecutive number. It can be up to 16 characters and may use letters, numbers, a hyphen or a slash.
• Invoice date.
• Customer details: name and address, and the customer's GSTIN if they are registered. For unregistered customers on larger invoices, the state and its code are also required.
• Description of goods or services, with the HSN code (goods) or SAC code (services) where applicable. Smaller businesses by turnover may need fewer digits of the HSN code, so check the current requirement for your turnover bracket.
• Quantity and unit for goods.
• Total value, any discount, and the taxable value.
• Tax rate and tax amount, shown separately as CGST, SGST/UTGST or IGST.
• Place of supply, and the state name if it differs from the delivery location.
• Signature or digital signature of the supplier or an authorised person.

CGST + SGST or IGST?

This depends on where the supply happens. If you and the customer are in the same state, the tax is split into CGST and SGST (for example 9% + 9% on an 18% item). If the supply crosses state lines, the full rate is charged as IGST. Getting this wrong is one of the most common invoicing mistakes, because it affects how your customer can use the credit.

Timing: when to issue the invoice

For goods, the invoice is generally raised at or before delivery. For services, the usual rule is to issue it within 30 days of providing the service (shorter for certain categories such as insurers and banks). Waiting until the customer chases you is a habit worth breaking.

Bill of supply, composition dealers and exempt sales

Not every sale needs a tax invoice. Businesses under the composition scheme issue a bill of supply and cannot charge GST separately. The same applies to fully exempt supplies. If you mix taxable and exempt items, issue separate documents or follow the format your tax advisor recommends.

E-invoicing

Businesses above a prescribed annual turnover threshold must report their B2B invoices to the government's Invoice Registration Portal and receive an IRN and QR code. The threshold has been lowered over the years, so confirm the current limit on the official GST portal rather than relying on an old figure.

Common mistakes to avoid

1. Skipping numbers or reusing an invoice number. Cancel an invoice instead of deleting it and keep a record.
2. Typing a customer's GSTIN incorrectly. Verify it on the GST portal before you issue the invoice.
3. Applying one tax rate to a mixed bill. Each line may carry its own rate.
4. Forgetting the place of supply on interstate sales.
5. Rounding inconsistently between the invoice and your books.

How software helps

A billing tool keeps your invoice series consecutive, stores customer details so you do not retype GSTINs, and calculates totals automatically. That removes most of the arithmetic and numbering errors above. You still need to choose the correct tax rate and codes for what you sell.

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