GST Invoice Format in India: Rules, Fields & Examples

A GST invoice is the official document a registered business issues for the supply of goods or services. Getting the format right matters because it lets your buyer claim input tax credit and keeps you compliant. Here is what a valid tax invoice must contain and how the tax is split.

Mandatory Fields in a GST Invoice

As of FY 2025-26, a tax invoice should generally include the following details. Always verify current requirements on the official GST portal, as rules can be updated.

Supplier details: name, address, and GSTIN of the seller
Invoice number and date: a unique, consecutive serial number for the financial year
Buyer details: name, address, and GSTIN (if the buyer is registered)
Place of supply and the state code, especially for inter-state sales
HSN code for goods or SAC code for services
Description, quantity, and unit of the goods or services
Taxable value and any discount applied
Tax rate and amount split into CGST, SGST/UTGST, or IGST
Total invoice value in figures, and the supplier's signature or digital signature

CGST + SGST or IGST: How to Decide

The type of tax depends on whether the transaction is within a state or between states:

Same-state supply (intra-state): the GST is split equally into CGST (Central GST) and SGST (State GST).
Inter-state supply: a single IGST (Integrated GST) is charged at the full rate.

So if the GST rate is 18%, a same-state invoice shows 9% CGST plus 9% SGST, while an inter-state invoice shows 18% IGST. The total tax is the same; only the split differs.

A Worked Example

Imagine a business in Maharashtra sells goods worth ₹10,000 at an 18% GST rate.

Case 1 - Buyer also in Maharashtra (same state):

Taxable value = ₹10,000
CGST at 9% = ₹900
SGST at 9% = ₹900
Total invoice value = 10,000 + 900 + 900 = ₹11,800

Case 2 - Buyer in Gujarat (different state):

Taxable value = ₹10,000
IGST at 18% = ₹1,800
Total invoice value = 10,000 + 1,800 = ₹11,800

The buyer pays ₹11,800 in both cases, but the tax is reported differently in your GST returns. You can create a clean, compliant bill in seconds using ToolSetu's free GST invoice generator.

Common Mistakes to Avoid

Skipping the HSN or SAC code. These are required for most businesses and help classify the supply correctly.
Breaking the invoice number series. Numbers must be consecutive and unique within the financial year.
Charging the wrong tax type. Always check the place of supply before choosing CGST+SGST or IGST.
Missing the buyer's GSTIN. Without it, a registered buyer cannot claim input tax credit.

Bill of Supply vs Tax Invoice

If you are a composition-scheme dealer or you supply exempt goods, you issue a bill of supply instead of a tax invoice, and you cannot charge GST on it. A regular registered supplier issues a full tax invoice with the tax split shown. Knowing which document applies to you avoids compliance trouble later.

When Must You Issue a GST Invoice?

The timing of the invoice depends on what you supply. As a general rule, for goods the invoice should be issued on or before the time of removal or delivery. For services, it is typically issued within a set number of days of providing the service. Issuing invoices promptly keeps your records clean and ensures your buyer can claim input tax credit in the correct return period. Late or missing invoices are a common reason for mismatches between your returns and your buyer's.

Rounding and Totals

Tax amounts can produce long decimals. The accepted practice is to round the final tax and total to the nearest rupee so the invoice is clean and the buyer pays a whole amount. Make sure the taxable value, the tax components, and the grand total all add up correctly, because mismatched totals can trigger queries during reconciliation. Keeping a consistent format across all your invoices also makes year-end filing far easier.

Conclusion

A correct GST invoice protects both you and your buyer: it ensures input tax credit flows smoothly and keeps your returns accurate. Remember the core rule: same-state means CGST plus SGST split equally, while inter-state means a single IGST. Include every mandatory field, keep your numbering consistent, and verify the latest format on the official GST portal whenever rules change.