GSTR-1 Filing for September 2026: Key Compliance Points for Monthly Filers and QRMP Taxpayers

GST-registered businesses must carefully track their GSTR-1 filing frequency and due dates. For taxpayers filing GSTR-1 monthly, the upcoming compliance deadline is 11 September 2026 for the August 2026 tax period, while the July–September 2026 quarter has a separate timeline for QRMP taxpayers.

Who Needs to File GSTR-1 Monthly?

GSTR-1 is the statement used to report details of outward supplies of goods and services.

Under the GST return framework:

• Taxpayers not covered by the QRMP scheme generally file GSTR-1 every month.
• Taxpayers with aggregate turnover exceeding Rs. 5 crore in the preceding financial year are not eligible for the QRMP scheme and therefore follow monthly return filing.
• Taxpayers with aggregate turnover up to Rs. 5 crore in the preceding financial year may opt for the QRMP scheme, subject to the prescribed conditions.

Notification No. 84/2020-Central Tax dated 10 November 2020 provides for the QRMP scheme for eligible registered persons having aggregate turnover up to Rs. 5 crore in the preceding financial year.

GSTR-1 Due Date for August 2026

For monthly filers, GSTR-1 is generally due on the 11th day of the succeeding month.

Accordingly:

• Tax period: August 2026
• Form: GSTR-1
• Filing frequency: Monthly
• Due date: 11 September 2026

The GST Portal's guidance confirms that GSTR-1 is generally due on the 11th day of the succeeding month for monthly filers. Notification No. 83/2020-Central Tax dated 10 November 2020 prescribed the monthly due-date framework.

What About the July–September 2026 Quarter?

The July–September 2026 period is the second quarter of FY 2026-27.

The filing requirement depends on the taxpayer's return frequency:

Monthly Filers

Taxpayers who are required to file monthly GSTR-1 will report their outward supplies separately for:

• July 2026 – GSTR-1 due on 11 August 2026
• August 2026 – GSTR-1 due on 11 September 2026
• September 2026 – GSTR-1 due on 11 October 2026

QRMP Taxpayers

Eligible taxpayers who have opted for QRMP furnish GSTR-1 quarterly. For the July–September 2026 quarter, the GSTR-1 due date is 13 October 2026, subject to any subsequent extension notified by the Government.

The GST compliance calendar for FY 2026-27 also reflects the 13th-of-the-following-month timeline for quarterly GSTR-1 and the 11th-of-the-following-month timeline for regular monthly filers.

What Details Should Be Checked Before Filing?

Businesses should reconcile their sales records before filing GSTR-1. Particular attention should be given to:

• B2B invoices and GSTIN details of customers
• B2C supplies
• Export and SEZ supplies, wherever applicable
• Credit notes and debit notes
• Amendments relating to earlier invoices
• Advances, where applicable
• HSN/SAC-wise reporting
• Document series and invoice numbers
• Taxable value and applicable GST rates
• Place of supply for relevant transactions

The GST Portal has also introduced changes to GSTR-1 reporting, including separate B2B and B2C tabs for HSN reporting in Table 12. Table 13, relating to documents issued, is mandatory where applicable from the May 2025 return period.

Importance of Accurate GSTR-1 Filing

GSTR-1 is not merely a sales-reporting form. Information reported by suppliers feeds into the GST system and contributes to the recipient's ITC reconciliation and GSTR-3B compliance.

The GST Portal confirms that several outward-supply liability figures in GSTR-3B are auto-populated from GSTR-1/GSTR-1A. Therefore, discrepancies between books, invoices and GSTR-1 should be identified and corrected promptly.

Taxpayers should also note that GSTR-1A provides an optional mechanism to amend or add certain records for the same tax period after GSTR-1 and before filing GSTR-3B.

Key Takeaway

For September 2026 compliance planning, businesses should first confirm whether they are monthly filers or have validly opted for QRMP. Monthly filers should ensure that the August 2026 GSTR-1 is filed by 11 September 2026, while eligible QRMP taxpayers will report the July–September 2026 quarter through GSTR-1 by 13 October 2026, unless the due date is subsequently extended.

Timely reconciliation of sales invoices, credit/debit notes, HSN details and customer GSTINs can help reduce errors and avoid downstream reconciliation issues.

For expert guidance on this topic, contact Us.