If you file monthly returns, your GSTR-1 for October 2026 is due on 11 November 2026 as per the statutory default. This GSTR-1 October 2026 checklist walks you through what to check, in what order, so that your outward supplies reach the GST portal complete and on time.
Because GSTR-1 feeds your customers' GSTR-2B, mistakes here do not stay with you. They show up as blocked or missing input tax credit for the buyer, and as phone calls to your accounts team.
1. Confirm the GSTR-1 October 2026 due date for your registration
For taxpayers filing monthly, GSTR-1 is due on the 11th of the following month, so 11 November 2026 for October. Taxpayers under the QRMP scheme file GSTR-1 quarterly, and may use the Invoice Furnishing Facility (IFF) to upload B2B invoices for the first two months of a quarter, usually by the 13th of the next month. The QRMP position for the July–September quarter is covered in our QRMP GSTR-3B checklist.
Due dates are sometimes extended by notification. Before you plan around 11 November, check the GST portal (gst.gov.in) and CBIC notifications (cbic-gst.gov.in) for any extension.
2. Close your September returns first
The portal can restrict you from filing GSTR-1 if earlier-period GSTR-3B returns are still pending. The September GSTR-3B falls due on 20 October, so finish it before you start October's outward supply return. Our September GSTR-3B pre-filing checklist will help you close that loop.
3. Make sure every sales invoice is on the books
Start with a simple completeness check, because GSTR-1 can only report what you have recorded.
- List the first and last invoice number for October in each invoice series and look for gaps.
- Account for cancelled invoices. A cancelled number should be clearly marked, not simply missing.
- Include invoices raised in October even if the goods moved or the payment came in November.
- Bring in advances received that attract tax, if your business receives them.
If your books are weak, our bookkeeping checklist for Indian SMEs is a good starting point.
4. Check the customer and invoice details line by line
Most GSTR-1 corrections come from a small set of data errors. Check these before you upload:
- Customer GSTIN: a wrong or inactive GSTIN means the invoice will not reach the right buyer's GSTR-2B.
- Place of supply: this decides whether you charge IGST or CGST plus SGST. A wrong state is one of the most common errors.
- Taxable value and rate: confirm the rate against the HSN or SAC code, and that discounts are shown correctly.
- Invoice number and date: use the exact number printed on the invoice, within the allowed character length and format.
- B2B versus B2C: supplies to registered buyers go under B2B. Supplies to unregistered buyers are reported as B2C, with large inter-state B2C invoices shown separately above the prescribed value limit.
5. Handle e-invoicing, if it applies to you
If your aggregate turnover crosses the notified e-invoicing threshold, B2B invoices must be reported to the Invoice Registration Portal, and they then flow into GSTR-1 automatically. In that case your task is to reconcile, not to re-enter. Compare the invoices auto-populated in GSTR-1 against your sales register, and chase any invoice that has no IRN. Confirm the current threshold on the official portal, since it has been revised over the years.
6. Review credit notes, debit notes and amendments
Credit notes and debit notes issued in October belong in this return. If you are correcting an invoice from an earlier month, use the amendment tables, and reference the original invoice carefully. Avoid editing the same invoice in several ways across months. It confuses both your records and your buyer's.
7. Fill in the HSN summary
The HSN summary needs the right number of digits for your turnover band. At the time of writing, smaller taxpayers report fewer digits than larger ones, but the rule has been amended, so check the current requirement on the portal. Make sure quantity, unit and taxable value in the summary tally with your invoices.
8. Reconcile totals before you file
- Match the GSTR-1 summary with your sales register for taxable value and tax by rate.
- Match IGST, CGST and SGST totals with your ledger.
- Keep the summary in your records, because your GSTR-3B should be consistent with it.
Later, you can check your suppliers' side of the story with our GSTR-2B and purchase register reconciliation guide. For the common GSTR-1 pitfalls in more depth, read How to File GSTR-1 Without Common Mistakes.
9. File, then verify the acknowledgement
Do not leave filing for the last evening. The portal is busiest right before the due date, and a one-day delay attracts a late fee for each day of default, plus a possible block on your buyers' credit. After filing, download the acknowledgement and the filed summary, and save them with your month-end records.
Key takeaways
- Monthly filers: GSTR-1 for October 2026 is due on 11 November 2026 by default. Check the portal for any extension.
- Close pending GSTR-3B returns first, since they can restrict GSTR-1 filing.
- Check GSTIN, place of supply, rate and invoice number on every invoice.
- Reconcile e-invoice data, credit notes and the HSN summary before filing.
- File early, and keep the acknowledgement with your records.
This article is general guidance, not professional advice. Confirm specifics for your business with your chartered accountant. If you want to see how a connected accounting tool could fit into this monthly routine, you can look at AICOUNTLY Smart Books.
