Think about this: you raise a GST invoice for ₹1,00,000 but later realise you overcharged, or the customer returned half the goods. How do you fix the tax already charged? That's exactly what credit notes and debit notes are for — they're the correction tools of GST.
A credit note is issued by the supplier when the original invoice was for more than it should have been. This happens in three situations: (1) the taxable value or tax was overcharged, (2) the buyer returned the goods, or (3) the goods/services were found deficient. When you issue a credit note, your output tax liability goes down — meaning you pay less GST. But here's the catch the examiners love: you can only issue a credit note up to 30th September following the end of the financial year of the original supply, or the date of filing the annual return (GSTR-9), whichever is earlier. Miss this deadline and you lose the ability to reduce your tax liability. Also critically — if you've already passed on the tax burden to your customer (i.e., they've paid the GST to you), you cannot reduce your output tax liability via a credit note. The benefit shouldn't come back to you when the customer already bore the cost.
A debit note works the opposite way — issued when the original invoice was for less than it should have been (undercharged). The supplier issues a debit note to the buyer, increasing the taxable value and tax. Important exam point: a supplementary invoice is treated as a debit note under the Explanation to this section. Unlike credit notes, there is no time limit for issuing debit notes — you can issue one any time, and it must be declared in the return for the month it's issued. This asymmetry between credit and debit notes is a very frequently tested 4-mark question in CA Inter.
Example 1 — Credit Note (Goods Returned)
Rajesh & Co. Pvt. Ltd. supplied goods to Ms. Iyer in October 2024 and raised a tax invoice for taxable value ₹5,00,000 + GST @18% = ₹90,000. Total invoice = ₹5,90,000.
Ms. Iyer returns goods worth ₹1,00,000 (taxable value) in January 2025 due to quality issues.
| Particulars | Amount |
|---|---|
| Taxable value of returned goods | ₹1,00,000 |
| GST @18% on returned goods | ₹18,000 |
| Credit Note value | ₹1,18,000 |
Rajesh & Co. must declare this credit note in GSTR-3B for January 2025 (the month of issuance). The last date to issue this credit note is 30th September 2025 (end of FY 2024-25 + 6 months) or the date of filing annual return, whichever is earlier.
Output tax liability of Rajesh & Co. reduces by ₹18,000, provided Ms. Iyer has not already claimed ITC on that ₹18,000 and the tax incidence hasn't been passed on.
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Example 2 — Debit Note (Undercharged Invoice)
Mr. Sharma raised an invoice on Mr. Verma in December 2024 for consulting services: taxable value ₹2,00,000 + GST @18% = ₹36,000.
Later it's discovered the correct value was ₹2,50,000.
| Particulars | Amount |
|---|---|
| Correct taxable value | ₹2,50,000 |
| Originally charged | ₹2,00,000 |
| Shortfall — Debit Note value | ₹50,000 |
| GST @18% on ₹50,000 | ₹9,000 |
Mr. Sharma issues a debit note / supplementary invoice for ₹50,000 + ₹9,000 = ₹59,000. There is no deadline for this debit note. It is declared in GSTR-1 and GSTR-3B for the month of issuance, increasing Mr. Sharma's output tax liability by ₹9,000.
📖 Bare Act text — Section 34, CGST Act 2017
(click to expand)
(1) [Where one or more tax invoices have] been issued for supply of any goods or services or both and the taxable value or tax charged in that tax invoice is found to exceed the taxable value or tax payable in respect of such supply, or where the goods supplied are returned by the recipient, or where goods or services or both supplied are found to be deficient, the registered person, who has supplied such goods or services or both, may issue to the recipient [one or more credit notes for supplies made in a financial year] containing such particulars as may be prescribed.
(2) Any registered person who issues a credit note in relation to a supply of goods or services or both shall declare the details of such credit note in the return for the month during which such credit note has been issued but not later than September following the end of the financial year in which such supply was made, or the date of furnishing of the relevant annual return, whichever is earlier, and the tax liability shall be adjusted in such manner as may be prescribed: Provided that no reduction in output tax liability of the supplier shall be permitted, if the incidence of tax and interest on such supply has been passed on to any other person.
(3) [Where one or more tax invoices have] been issued for supply of any goods or services or both and the taxable value or tax charged in that tax invoice is found to be less than the taxable value or tax payable in respect of such supply, the registered person, who has supplied such goods or services or both, shall issue to the recipient [one or more debit notes for supplies made in a financial year] containing such particulars as may be prescribed.
(4) Any registered person who issues a debit note in relation to a supply of goods or services or both shall declare the details of such debit note in the return for the month during which such debit note has been issued and the tax liability shall be adjusted in such manner as may be prescribed.
Explanation.––For the purposes of this Act, the expression ―debit note‖ shall include a supplementary invoice.