GSTR-1 explained: tables, due dates, IFF, GSTR-1A and common mismatches

GSTR-1 is the return in which a registered business reports its outward supplies: sales invoices, credit and debit notes, exports, advances and a summary by HSN code. Every regular GST-registered business files it; composition dealers file other returns. As of November 2026, monthly filers file GSTR-1 by the 11th of the next month, and quarterly filers under the QRMP scheme by the 13th of the month after the quarter. What you report as B2B in GSTR-1 becomes your buyers’ GSTR-2B, the statement that decides their input tax credit.

What goes into GSTR-1

Table	Section	What you report
4, with 6B and 6C	B2B	Invoices to registered buyers, one by one, including reverse-charge supplies, SEZ supplies and deemed exports
5	B2CL	Inter-state invoices to unregistered buyers above ₹1 lakh each (as of November 2026)
6A	Exports	Export invoices, with or without IGST, with shipping bill details
7	B2CS	All other sales to unregistered buyers, summarised by state and tax rate
8	Nil-rated, exempt and non-GST	Totals of such supplies
9B	CDNR and CDNUR	Credit and debit notes to registered buyers (CDNR), and to unregistered buyers against B2CL or export invoices (CDNUR)
9A, 9C and 10	Amendments	Changes to invoices, notes and B2CS figures of earlier periods
11	Advances	Tax on advances received, and their adjustment
12	HSN summary	Quantity, value and tax for each HSN code
13	Documents issued	Serial number ranges of each document type, with cancelled numbers

A few practical points:

• B2B or B2C depends on the buyer’s GSTIN. If the GSTIN is missing from the party master, a B2B sale lands in B2CS and your buyer loses the credit.
• HSN digits depend on turnover. Businesses above ₹5 crore report 6-digit HSN codes; smaller ones report 4 digits. The portal has tightened this table in recent years, so check its current format before you file.
• E-invoices are filled in for you. If you e-invoice, the B2B, CDNR and export rows come from the IRP. Review them, and do not upload them again. See What is e-invoicing.

Due dates

Filing option	Form	Due date (as of November 2026)
Monthly	GSTR-1	11th of the next month
QRMP (turnover up to ₹5 crore)	IFF for months 1 and 2, optional	1st to 13th of the next month
QRMP	GSTR-1 for the quarter	13th of the month after the quarter
Both	GSTR-1A, optional	After GSTR-1, before GSTR-3B of the same period

Example for October 2026: a monthly filer files GSTR-1 by 11 November 2026. A QRMP filer can upload October’s B2B invoices through IFF between 1 and 13 November 2026, and files GSTR-1 for October to December by 13 January 2027.

Three more points on timing:

• The government sometimes extends due dates by notification, so check the GST portal near each date.
• A nil GSTR-1 must be filed even when there are no sales.
• You cannot file GSTR-1 for a period while GSTR-3B for the previous period is pending.

IFF for quarterly filers

The Invoice Furnishing Facility (IFF) lets a QRMP filer upload B2B invoices for the first two months of the quarter. It is optional, but it helps your buyers: invoices you upload through IFF reach their GSTR-2B every month instead of once a quarter. Buyers who release payment only after they see the credit will notice the difference.

GSTR-1A: fixing the same period

GSTR-1A is an optional form to add records you missed, or correct records you reported, in GSTR-1 for the same tax period. You can file it after GSTR-1 and before GSTR-3B for that period, and the changes flow into that period’s GSTR-3B. After GSTR-3B is filed, corrections go through the amendment tables of a later GSTR-1.

GSTR-1A is becoming more important. GSTN has announced that the liability auto-filled into GSTR-3B from GSTR-1 will be locked, which makes GSTR-1A the place to correct it. Check the latest advisory for the current position. More in GSTR-3B explained.

Common mismatches and how to avoid them

1. Missing or wrong buyer GSTIN. The sale goes to B2CS, or to the wrong buyer’s GSTR-2B. Check GSTINs when you create a party.
2. Wrong place of supply. IGST charged on a sale within the state, or CGST and SGST on an inter-state sale. Check the party’s state and your tax ledgers.
3. GSTR-1 and GSTR-3B do not agree. A large gap between the liability in GSTR-1 and the tax paid in GSTR-3B can bring an intimation in form DRC-01B asking you to pay or explain.
4. Books, e-invoices and e-way bills tell different stories. Editing auto-filled e-invoice data, or leaving invoices unregistered, creates gaps the department can see.
5. The HSN summary does not match the invoices. Quantities and values in Table 12 should add up to your invoice totals.
6. Credit notes are missing. Unreported credit notes overstate your tax.
7. Invoices fall in the wrong period. A wrong date moves tax from one return to another.

One habit prevents most of these. Before filing, compare the GSTR-1 prepared from your books with what the portal already holds, and settle every difference.

How Auditer helps

Auditer prepares GSTR-1 from your TallyPrime books and shows it beside what the GST portal already holds, including registered e-invoices, so differences are visible before you file. Under Settings, the Owner decides whether Auditer only prepares the return, saves a draft on the portal, or files it with an EVC; filing is done from the web portal. A due-date calendar and a compliance score keep each period in view. Auditer does not file GSTR-1A or amend filed returns, so do those on the GST portal. See GST compliance.

This article is general information, not tax advice. GST rules change; check the GST portal or your tax professional before acting.