When Must a GST Invoice Be Issued? Time of Supply Rules Explained

Goods

Where the supply involves movement of goods, Section 31(1) requires the invoice to be issued before or at the time of removal for delivery. Where it does not involve movement, the invoice is issued on delivery or when the goods are made available to the recipient.

Since Notification 66/2017, tax on goods is not payable on advances. The liability arises on the invoice, which makes the removal date the operative trigger for almost all goods businesses.

Services

Section 31(2) read with Rule 47 requires the invoice within thirty days of the supply of the service. For insurers, banking companies, financial institutions and non-banking financial companies the window is forty-five days.

Unlike goods, tax on services IS payable on advances. Receiving money before supplying triggers a receipt voucher and a liability in that period, with the invoice following when the service is actually supplied.

Continuous supply

A continuous supply of services — a retainer, a maintenance contract, a subscription — is invoiced by reference to the contract. Section 31(5) provides three cases:

For a continuous supply of goods involving successive statements of account, the invoice is issued before or at the time each statement is issued or each payment is received.

• Where the due date of payment is ascertainable from the contract: on or before that due date.
• Where it is not ascertainable: on or before the date the supplier receives payment.
• Where payment is linked to completion of an event: on or before the date of completion of that event.

Reverse charge and unregistered suppliers

Where tax is payable by the recipient under reverse charge, the recipient issues a self-invoice on the date they receive the goods or services, if the supplier is unregistered. They also issue a payment voucher at the time of making payment.

The time of supply under reverse charge is the earliest of the date of receipt of goods, the date of payment, or thirty days from the supplier's invoice date for goods — sixty days for services.

The thirty-day e-invoicing clock is separate

If e-invoicing applies to you and your turnover is ten crore rupees or more, the invoice must additionally be reported to the Invoice Registration Portal within thirty days of the document date. That window runs from the invoice date, not from the supply date, and the portal simply rejects anything older.

An invoice issued on time but reported late therefore fails anyway, because without an IRN it is not a valid tax invoice.

Frequently asked questions

### What happens if a GST invoice is issued late?

The liability still arises by reference to the time of supply, so a late invoice generally means the tax belonged to an earlier period. That brings interest at eighteen per cent under Section 50 on the delayed payment, and a penalty under Section 122 for failing to issue an invoice within the prescribed time.

### Can I backdate an invoice to the previous month?

No. Backdating misstates the time of supply and, where e-invoicing applies, is simply impossible — the portal computes the IRN from the document date and rejects anything beyond the thirty-day reporting window. Where the supply genuinely belonged to an earlier period, report it correctly and pay the interest rather than altering the date.

### Do I pay GST on an advance received for goods?

No, not since Notification 66/2017. For goods, the liability arises when the invoice is issued. For services the position is different: tax is payable on the advance, and you issue a receipt voucher under Section 31(3)(d) at the time of receiving it.