If you file GST monthly, November has two dates that matter for the October tax period: GSTR-1 is usually due on the 11th and GSTR-3B on the 20th. File them in that order, with a reconciliation in between, and most last-minute mismatches disappear.
This GST November checklist walks through one routine for monthly filers. Dates here are the statutory defaults; extensions are sometimes notified, so confirm on the GST portal (gst.gov.in) before you plan around them.
The two dates for the October 2026 tax period
ReturnWhat it reportsUsual due date GSTR-1Your outward supplies (sales) for the month11 November 2026 GSTR-3BSummary of sales, eligible ITC and the tax you pay20 November 2026The due date for GSTR-3B can differ for QRMP (quarterly) filers and by state group, so this routine is written for monthly filers. If you are on QRMP, read our guide to QRMP GSTR-3B due dates and payments instead.
Step 1: Close the month's sales before the 11th
GSTR-1 is only as good as your sales register. Before you open the portal, check that every invoice, credit note and debit note dated in October is entered and that none belongs to another month.
- Look for gaps in invoice numbers. A missing number should have a reason, such as a cancelled invoice.
- Check that each B2B invoice carries the customer's correct GSTIN and place of supply.
- Confirm HSN/SAC codes and tax rates on the lines, especially for items you sold for the first time this month.
- Make sure advance receipts and adjustments are recorded, since they are reported separately.
Our checklist of mandatory tax invoice fields under Rule 46 is a useful companion for this step.
Step 2: File GSTR-1 on or before the 11th
Once your register is clean, prepare GSTR-1 and compare its totals with your books before you submit. Two quick comparisons catch most errors:
- Total taxable value and total tax in GSTR-1 against the sales and output tax ledgers for October.
- The number of B2B invoices in GSTR-1 against your register.
Remember that GSTR-1 data flows to your customers' GSTR-2B. An invoice you leave out, or report with a wrong GSTIN, can stop them from claiming credit, and they will ask you why. For a deeper look at common slips, read how to file GSTR-1 without common mistakes.
Step 3: Download GSTR-2B and reconcile your purchases
GSTR-2B is the static statement of input tax credit available to you for the month. It is generated after the due date of the suppliers' GSTR-1, so check on the portal that the October statement is available before you start.
Match it against your purchase register:
- In 2B and in your books: usually fine to claim, subject to the usual conditions.
- In 2B but not in your books: check whether you received the goods or services, and whether the bill is missing from your register.
- In your books but not in 2B: the supplier may not have filed yet or may have reported it wrongly. Follow up before claiming the credit.
Our step-by-step guide to GSTR-2B and purchase register mismatches explains this matching in detail.
Step 4: Check credit you cannot claim or must reverse
Before settling the ITC figure for GSTR-3B, go through two categories that are easy to miss:
- Credit that is blocked under Section 17(5). See purchases on which you cannot claim GST ITC.
- Credit to reverse where a supplier has not been paid within the time limit. See the 180-day rule under Rule 37.
Also keep in mind the time limit for claiming credit on invoices of the previous financial year, covered in our post on the Section 16(4) deadline of 30 November 2026.
Step 5: Compare GSTR-1 with your GSTR-3B working
The outward supply figures in GSTR-3B should agree with what you just filed in GSTR-1, unless you have a documented reason. Differences usually come from credit notes, amendments, or invoices booked in the wrong month. Use the GSTR-1 vs GSTR-3B reconciliation checklist to find and fix them, and write down the explanation for any difference that remains.
Step 6: Pay the tax and file GSTR-3B by the 20th
GSTR-3B liability is paid first from the electronic credit ledger and the balance in cash, using the rules the portal applies. Check your electronic cash ledger balance a few days ahead so that you can create the challan in time. If you are covered by Rule 86B, a part of the liability must be paid in cash, so read when you must pay 1% of output tax in cash.
Filing late attracts a late fee and interest on the unpaid tax. We have worked through the numbers in GST late fee and interest on GSTR-3B.
Step 7: Keep a short record of the month
After filing, save the acknowledgements and the working papers for the month in one place: the sales register, the 2B reconciliation, the challan and the ARN for each return. A one-page note listing what you changed and why helps your accountant or CA during year-end review and any GST notice later.
Key takeaways
- For October 2026, monthly filers usually file GSTR-1 by 11 November and GSTR-3B by 20 November; confirm any extension on the GST portal.
- Clean the sales register first, then file GSTR-1, then reconcile purchases with GSTR-2B.
- Check blocked credit and reversals before fixing the ITC figure.
- Compare GSTR-1 with GSTR-3B and note every difference.
- Arrange cash for the tax payment early, and keep ARNs and working papers together.
If you keep your books in Smart Books, it has a GST return view where you can review your GSTR-1 data for a chosen filing period, with monthly or quarterly frequency, next to the vouchers behind it. This article is general guidance; please confirm specifics for your business with a chartered accountant.
