Debit note format: the supplementary invoice for an undercharge
A debit note is the mirror image of a credit note: it increases the value or tax of an invoice that charged too little. Section 34(3) covers the common cases — a rate revision, a quantity short-billed, a cost agreed after the invoice, or a wrong rate applied at the time of supply. It is often called a supplementary invoice, and it must reference the original invoice so the buyer can match the additional tax to the supply and claim the credit. Unlike a credit note, there is no 30 November cut-off, but the additional tax has to be declared in the return for the period in which the note is issued, so delaying it only postpones the liability and any interest that comes with it.
Frequently asked questions
What is a debit note?
A debit note is a document that increases the value or tax of an earlier tax invoice. Section 34(3) of the CGST Act allows it where the value or tax charged on the invoice was less than what is actually payable — an undercharge, a rate revision, or a charge added after the supply. It is often called a supplementary invoice, because it adds to the original rather than replacing it.
When should I issue a debit note?
Issue one when you discover that an invoice undercharged — a wrong rate, a missing line, a quantity short-billed, or a cost that was agreed after the invoice. Also use it when a rate revision applies to a supply already invoiced and the additional amount is still payable. Do not use it to bill a new supply; that needs its own tax invoice.
What is the difference between a debit note and a credit note?
A debit note increases the value of the earlier invoice; a credit note reduces it. Both are issued under Section 34 and both must reference the original invoice. The direction matters for the tax return: a debit note adds to your output liability, while a credit note reduces it. Issuing the wrong one produces a mismatch that is easy to see and hard to explain.
Is there a time limit for a debit note?
There is no equivalent of the 30 November cut-off that applies to credit notes. The additional tax must be declared in the return for the period in which the debit note is issued, and it should be raised as soon as the undercharge is identified. Delaying it does not make the liability disappear; it only pushes the tax and any interest further out.
Does a debit note increase the buyer's input tax credit?
Yes, where the supply is eligible for credit and the supplier reports the debit note. The additional tax appears in the buyer's GSTR-2B for the period, and the buyer can claim it in the same way as the original invoice. If the supplier does not report it, the buyer has a document but no credit — which is why the note has to be filed, not just sent.
Is a debit note the same as a supplementary invoice?
In practice, yes. "Supplementary invoice" is the commercial name for the same document: an invoice that adds to an earlier one. GST law uses "debit note" in Section 34(3), and the tax treatment follows that section. Use one term consistently in your books so the original invoice, the debit note and the return all reconcile.
Can I raise a debit note after the financial year?
Section 34(3) does not impose the credit note cut-off, so a debit note can be raised after the year in which the supply was made. The additional tax is still declared in the return for the period in which the note is issued, and interest may apply if tax was payable earlier. Raise it as soon as the error is found rather than waiting for a reconciliation.
Does a debit note need the original invoice reference?
Yes. The original invoice number and date are what let the buyer match the note to the supply and what let the department reconcile the additional tax. A debit note without that reference is just a fresh demand with no link to a supply, and the buyer's accountant will usually hold the payment until the link is clear.