A customer walks back in with last Tuesday's purchase. Or you spot that Tuesday's bill charged ₹1,200 for something that sells at ₹1,020. The tempting fix is obvious: open the old invoice, correct the line, reprint it. Do not. An issued GST invoice is a filed fact. Once it exists, the law does not want it edited. It wants a second, smaller document issued against it.
Never edit an issued invoice: what Section 34 asks for instead
Section 34 of the CGST Act is the whole rule. When the taxable value or the tax on an invoice turns out to be more than it should have been, or the goods come back, or the goods or services are found deficient, the supplier issues a credit note against that invoice. When the value or tax turns out to be less than it should have been, the supplier issues a debit note. The original invoice stays exactly as printed: same number, same date, same amounts.
Why so strict? Because your invoice has a life beyond your counter. It sits in your GSTR-1, and if the buyer is registered, it feeds their input tax credit. Silently rewriting it leaves the government and your buyer holding a version of events that no longer matches yours. The credit or debit note is the audit trail: anyone can see what was billed, what changed, and why. The same logic covers a bill you want to scrap entirely; we have written separately about what happens to a cancelled invoice number.
Credit note or debit note: which one and when
One question decides it: after the correction, does the customer owe you less or more?
- Credit note: the customer owes less. Goods returned, an overcharge, a quantity billed but not delivered, a rate typed wrong on the high side, damaged stock the buyer kept at a discount. You are giving value back.
- Debit note: the customer owes more. You undercharged, missed a line, or applied a lower tax rate than the item carries. A supplementary invoice does the same job here; Section 34(3) treats them alike.
The names confuse people because accountants use them from both sides of the ledger. Under GST the convention is fixed: Section 34 speaks of notes issued by the supplier. You sold, so you issue. The buyer does not issue a GST credit note back at you.
A counter sales return, step by step
Say a customer returns one of three items from bill number 214, worth ₹500 plus ₹60 GST.
- Take the goods back into stock. If you track batches, back into the right batch, so expiry reports stay honest.
- Issue a credit note referencing invoice 214: the returned item, its value ₹500, and the ₹60 tax reversed with it. Rule 53(1A) of the CGST Rules lists what the note must carry, including the serial number and date of the invoice it corrects.
- Refund the ₹560, or park it against the customer's ledger if they buy on credit.
- Leave invoice 214 untouched. It still shows three items, and that is correct: it records what happened on Tuesday, and the credit note records what happened today.
Since the amendment effective 1 February 2019 (CGST Amendment Act, 2018), one credit note may cover several invoices, which is a real convenience for a distributor whose retailer returns a mixed carton against last month's bills. If most of your billing is wholesale billing to registered buyers, that one change saves paperwork every month.
The credit note deadline you should not miss
A debit note can be issued whenever the mistake surfaces; it only adds tax, and the government does not object to receiving more. A credit note that reduces your tax has a clock on it. Under Section 34(2), the note must be declared in a return by 30 November following the end of the financial year in which the original supply was made, or the date you file that year's annual return, whichever comes first.
One more condition hides in Section 34(2): your tax reduction is not allowed if the burden of that tax was passed on and stays passed on. In practice, for a B2B note, your registered buyer must reverse the input tax credit they took on the reversed portion. If they do not, expect the mismatch to surface when returns are compared.
Where the notes appear in GSTR-1
Notes issued to registered buyers are reported document by document in the credit and debit note table of GSTR-1 (Table 9B), each one naming the buyer's GSTIN. Notes against unregistered, walk-in sales do not get their own line each; consumer sales enter GSTR-1 as consolidated figures, and the return-period figures absorb the reduction, with the unregistered-note table reserved for the large interstate consumer invoices that were itemised in the first place.
GSTR-3B then carries the net effect in its outward supply figures. This is exactly the kind of adjustment that makes the two returns disagree when a note is reported in one and forgotten in the other; if your accountant has ever called about that, our post on GSTR-1 versus GSTR-3B mismatches walks through how the gap opens and how to close it.
Numbering the notes: their own series, not the invoice series
A credit note is a document in its own right, and Rule 53(1A) asks the same of it as Rule 46 asks of an invoice: a consecutive serial number, up to sixteen characters, unique for the financial year. Give your notes their own series (CN-001, CN-002, and DN-001 for debit notes) rather than borrowing numbers from the invoice series. A credit note numbered like an invoice creates a gap-shaped puzzle in your invoice sequence and an awkward conversation at assessment time. The note then refers to the invoice it corrects; it never replaces or reuses its number.
This is also where software should quietly do the right thing. In Layerdots ERP the original bill stays immutable in your bill history, the return produces its own document against it, stock walks back into inventory, the customer ledger updates, and the GST reports pick the adjustment up in the right period. The point is not the automation; it is that the correct path costs no more effort than the wrong one.
Common questions
The customer paid cash and has no GSTIN. Do I still need a credit note?
Yes, document it. Section 34 does not exempt consumer sales, and your stock and daily totals
will not add up without it. The difference is only in reporting: it will not appear
buyer-by-buyer in GSTR-1 the way a B2B note does, but it must still reduce the consolidated
consumer figures for the period, and the note itself is your record of why.
Can one credit note cover several invoices?
Yes, since 1 February 2019. Section 34 as amended speaks of "one or more credit notes" against
"one or more tax invoices" in the same financial year. Your records should still make clear
which invoices the note settles, because a registered buyer has to match their credit reversal
against it.
I found a 2024-25 overcharge today. Is it too late?
For the GST part, yes: the Section 34(2) window for 2024-25 supplies closed on
30 November 2025 (or on your annual return date, if earlier). You can still make the customer
whole with a commercial credit note that carries no GST adjustment. For the money owed between
you, that works fine; the tax you collected simply stays with the government.