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An accountant finds gaps and a cancelled invoice in the sales series and does not know whether the numbers can be skipped, reused or must be explained.
Rule 46 requires a consecutive serial number of up to 16 characters, unique for the financial year. Cancelled numbers stay in the series and are reported as cancelled in the GSTR-1 documents-issued table.
Keep one register per series listing from-number, to-number, cancelled numbers with reasons, and the net count, and tie it to the sales register each month.
A series that explains every number: issued, cancelled or skipped, and a documents-issued table that matches the sales register and the auditor's query.
No, you cannot reuse a GST invoice number, and you should not skip one without a record. Rule 46 of the CGST Rules says a tax invoice needs a consecutive serial number of up to 16 characters, using letters, numerals, the hyphen (-) and the slash (/), unique for the financial year. A cancelled invoice keeps its number and is reported as cancelled. It is never given to a new sale.
This trips up many junior accountants in their first GST month-end. The good news: gaps and cancellations are allowed as long as you can explain each one.
Why does a series have gaps or repeats?
| Cause | Allowed? | What to do |
|---|---|---|
| Invoice cancelled before the goods left | Yes | Keep the number, mark it cancelled, report it in the documents-issued table |
| Software skipped a number after a failed save or upload | Yes, with a record | Treat it as cancelled and note the reason in your series register |
| Two invoices given the same number | No | Cancel one and reissue it under the next number before filing GSTR-1 |
| A separate series for each branch or for exports | Yes | Rule 46 allows multiple series; report each series separately |
| Series restarts every 1 April | Yes | Add the year to the prefix (INV/26/…) so numbers stay unique |
| Number longer than 16 characters | No | Shorten the prefix; the IRP also rejects longer document numbers |
How do cancelled and missing numbers show up in GSTR-1?
GSTR-1 has a documents-issued table (Table 13). For each series you report the first number, the last number, the total issued, the number cancelled and the net issued. Nothing is hidden; the tax officer sees exactly how many numbers were voided.
If you issue e-invoices, a cancelled IRN also drops out of the invoice tables that are auto-filled from the Invoice Registration Portal. The documents-issued table is where the cancelled number still appears.
What happens if two invoices carry the same number?
Three things go wrong:
- The IRP rejects the second document if e-invoicing applies to you, because the document number, type and year must be unique for your GSTIN.
- On GSTR-1 the portal flags a duplicate invoice number, so the return cannot carry both lines.
- Your buyer cannot match the invoice in GSTR-2B against the purchase register, because two different amounts sit under one number.
The fix is to cancel one invoice (or issue a credit note if the period is closed) and raise it again under the next free number.
Worked example: series INV/26/0001 to 0150
A trader in Pune runs one series for 2026-27. By the end of May the numbers run from INV/26/0001 to INV/26/0150.
- INV/26/0047 was raised for ₹47,200 and cancelled the same day because the customer changed the order.
- INV/26/0098 does not exist anywhere. The billing software crashed during the save and moved straight to 0099.
Here is how the three records line up:
| Record | What it shows |
|---|---|
| Sales register | 148 invoices |
| GSTR-1 Table 13 | From 0001 to 0150, total 150, cancelled 2, net issued 148 |
| Series register (your own note) | 0047 cancelled, customer change; 0098 skipped, software crash on 22 May |
150 numbers minus 2 cancelled equals 148, which equals the sales register count. When the auditor asks, “Why is 0098 missing?”, the series register gives the answer in one line. Without it, the gap looks like a suppressed sale.
A simple monthly check
- Export the sales register sorted by invoice number.
- Count from the first to the last number in each series.
- List every number not in the register and give each a reason.
- Confirm the net count equals the GSTR-1 documents-issued figure before you file by the 11th (or the 13th for quarterly QRMP filers).
Key rules to remember
- Invoices are issued under Section 31 of the CGST Act, with particulars set by Rule 46.
- An invoice already reported in a filed GSTR-1 is reversed through a credit note under Section 34, declared by 30 November following the financial year.
- If you issue e-invoices (turnover above ₹5 crore), the IRP rejects a repeated document number, and at ₹10 crore or more it rejects documents older than 30 days.
What to read next
- Next in this series: What is a GST tax invoice, and what must it contain?
- Match documents issued with IRN records: E-invoice reconciliation in India
- Before filing: GSTR-1 vs GSTR-3B reconciliation failure modes
- GST reconciliation software: GST outward reconciliation (GSTR-1 and GSTR-3B) leads the TransactIG GST roadmap.