Credit note or debit note? How to fix a GST invoice after it has gone out

Once a tax invoice has gone to a registered buyer, two sets of books depend on it. Yours shows the tax you owe, and theirs shows the input tax credit they will claim. Both of you report the same invoice to the GST portal, and the portal matches the two. If you quietly change the amount on your copy, the numbers stop matching and someone gets a notice.

So the law gives you two separate documents for fixing an invoice after the fact. A credit note brings the value down. A debit note takes it up. The original invoice stays exactly as it was, and the note sits on top of it.

Ask one question: after the correction, does your customer owe you more money or less?

Less: issue a credit note

• The customer sent some of the goods back.
• You charged a higher price or a higher tax rate than you should have.
• Part of the order was damaged, short or not up to the agreed quality, and you agreed to knock it off.
• You gave a discount after the sale, for example a year-end volume discount.

More: issue a debit note

• You billed a lower price than the one you had agreed.
• You sent more than the invoice shows and the customer is keeping it.
• You applied a lower tax rate than the item carries.

If the whole invoice was wrong from the start (the wrong customer, say, or an order that was never delivered), a note is usually not the cleanest fix. Cancel the invoice and issue a fresh one, and keep the reason on record.

A Surat wholesaler sells 20 cotton shirts at ₹500 each to a retailer in the same state, at 5% GST.

A week later the retailer returns 4 shirts with a printing fault. The wholesaler issues a credit note against the original invoice:

Now suppose instead that the agreed price was ₹550 a shirt and the invoice said ₹500 by mistake. The retailer keeps all 20, so they owe more. That is a debit note for 20 × ₹50 = ₹1,000 of taxable value, plus CGST ₹25 and SGST ₹25, which is ₹1,050 in all.

Rule 53 of the CGST Rules lists the details. In plain words, every credit or debit note needs:

1. Your name, address and GSTIN.
2. What the document is: the words Credit Note or Debit Note at the top.
3. Its own serial number, up to 16 characters and never repeated in the financial year. Most businesses keep a separate series, like CN/26-27/001.
4. The date you issue it.
5. The customer’s name, address and GSTIN if they are registered. For an unregistered customer, their name, address and the state with its code.
6. The number and date of the invoice (or invoices) it corrects.
7. The taxable value being added or taken off, the tax rate and the tax amount.
8. Your signature or digital signature.

The one people forget is the link to the original invoice. Without it, your customer’s accountant cannot tell what the note is correcting, and you will get a phone call.

A credit note that reduces your tax has a cut-off. You have to declare it by 30 November after the end of the financial year in which the original sale happened, or by the date you file your annual return for that year if you file it earlier. For a sale made in 2025-26, that means 30 November 2026 at the latest.

Miss it and you can still give the customer the money back, but you can no longer reduce your own GST for it. You end up paying tax on a sale that, in practice, shrank.

Debit notes have no similar cut-off on your side: you are adding tax, and nobody minds that. The time limit falls on your customer instead. They can claim the extra input tax credit only up to 30 November after the end of the financial year in which the debit note was issued. Since 2021 that clock starts from the debit note’s own date, not from the original invoice.

Year-end and volume discounts have long been the messiest kind of credit note, because the rules tied them to an agreement made before the sale. The Finance Bill 2026 proposed loosening this, so that a credit note plus the buyer’s reversal of credit would be enough. Check with your accountant whether the change is in force before you plan a discount scheme around it.

Both kinds of note go into your GSTR-1 for the month (or quarter) in which you issue them, alongside your invoices. Your customer sees them in their own statement and adjusts their credit to match.

In Invoiceo, open the invoice and choose Credit note or Debit note. The note is linked to the invoice, picks up the customer and the tax split, and gets its own number. You can send returned goods back into stock, and the invoice’s balance changes to show what is still owed. If you just need to check the tax on an adjustment, the GST calculator does that on its own.