GST Invoice Guide for India: Fields, CGST, SGST and IGST Explained

The fields a GST invoice needs

The CGST Rules set out the particulars a tax invoice must show. For a registered supplier issuing an invoice to a registered buyer, the core fields are:

• The supplier's name, address and GSTIN
• A serial number that is unique for the financial year, up to 16 characters, using letters, numbers, hyphens and slashes
• The date of issue
• The recipient's name, address and GSTIN, where the buyer is registered
• The place of supply and, for interstate supplies, the state
• A description of the goods or services, with the HSN code for goods or the SAC code for services
• Quantity, unit and the taxable value after any discount
• The rate and amount of each tax: CGST and SGST, or IGST
• The total invoice value
• The signature or digital signature of the supplier

Rules for unregistered buyers, for invoices above certain thresholds, and for specific supply types are more detailed. Check the current rules before issuing invoices for those cases.

How CGST, SGST and IGST are applied

GST is a single tax on the supply, but the revenue is shared between the central and state governments. Which components apply depends on where the supplier and the place of supply are.

For an intrastate supply, where both parties are in the same state, the tax is split equally into CGST, which goes to the centre, and SGST, which goes to the state. A 18 percent rate, for example, is shown as 9 percent CGST and 9 percent SGST.

For an interstate supply, where the supplier and the place of supply are in different states, the full rate is charged as IGST. The same 18 percent rate appears as 18 percent IGST. Union territories without a legislature follow the UTGST rules in place of SGST, so check which applies to the place of supply.

Getting this split wrong is one of the most common invoice errors. If an intrastate sale shows IGST, the buyer may be unable to claim the credit correctly, and you may have to issue a corrected invoice or a credit note.

Rates depend on the goods or services

Each product or service falls under a GST rate. The government revises the rate schedule from time to time, so do not rely on a rate you saw in an old article or a template. Look up the HSN or SAC code on the official GST portal, confirm the current rate, and then apply it to each line.

If one invoice covers goods at different rates, show each line at its own rate and give the tax summary by rate. Mixing rates on one line is a fast way to make the invoice wrong.

Invoice numbering and time limits

Use one unique, consecutive series for each financial year. Do not skip numbers without a reason you can explain, and do not reuse a number after cancelling an invoice. If you need to correct an invoice, issue a credit note or a corrected invoice under the rules, and keep the original on record.

The invoice must be issued within the time limit set by the rules for the type of supply. Delays can create compliance issues even when the amounts are correct.

E-invoicing and the reporting requirement

Businesses above a turnover threshold must generate an e-invoice through the government invoice registration portal, which returns an Invoice Reference Number and a signed QR code. The threshold has been lowered over time, so check the current limit for your business.

A PDF created in a generic tool does not replace the e-invoice where it is mandatory. Small businesses below the threshold can continue to issue ordinary tax invoices, but the fields above still apply.

Common mistakes that cost your client money

• Showing CGST and SGST on an interstate sale, or IGST on an intrastate sale
• Leaving out the buyer's GSTIN when the buyer is registered
• Using a serial number that repeats or has more than 16 characters
• Applying the wrong HSN or SAC code, or none at all
• Forgetting that discounts reduce the taxable value, not the tax rate
• Issuing a new invoice for a correction instead of a credit note, which leaves two valid-looking invoices for the same sale

If you fix one thing, fix the tax split. It is the field buyers check first and the one that causes the most disputes.

Using a template safely

A template saves time, but it does not know the rules for your business. Before you rely on any template, check that it includes every required field, that it applies the tax split based on the place of supply, and that it lets you enter HSN or SAC codes per line. Keep a PDF of every invoice you issue, and make sure your records match the amounts you declare in your GST returns.

This guide is general information, not tax advice. For a specific transaction, speak to a chartered accountant or GST practitioner.