Miss your GSTR-1 deadline by even one day and you are paying ₹50 per day in late fees - ₹25 under CGST and ₹25 under SGST. Miss it long enough and your buyers lose their Input Tax Credit, your E-Way Bill generation gets blocked, and your GST registration faces suspension. For a return that most businesses treat as routine paperwork, GSTR-1 carries consequences that can cripple your operations.

This guide breaks down everything you need to know about GSTR-1 - what it is, who must file, the exact deadlines for FY 2026-27, the recent CBIC changes that made accuracy non-negotiable, and how to avoid the penalties that catch thousands of Indian businesses every quarter.

What Is GSTR-1 and Why Does It Matter?

GSTR-1 is the Statement of Outward Supplies - a mandatory return under the CGST Act, 2017 (Section 37) that every registered taxpayer must file to report all sales, exports, and outward supplies made during a tax period.

Here is what GSTR-1 captures:

Why does this matter beyond compliance? Because GSTR-1 is no longer just your filing - it directly feeds your buyer's GSTR-2B (auto-populated purchase register). If you report an invoice incorrectly or miss it entirely, your buyer cannot claim ITC on that transaction. This creates a chain reaction: your buyer contacts you, you file amendments, and meanwhile both businesses face reconciliation headaches.

Since July 2025, CBIC has hard-locked GSTR-3B Table 3 (outward supply liability) to GSTR-1 data. You cannot manually override these figures anymore. What you report in GSTR-1 is what flows into your tax liability - no corrections possible in GSTR-3B itself.

Who Must File GSTR-1?

Every person registered under GST as a normal taxpayer or casual taxable person must file GSTR-1. This includes:

Who is exempt from GSTR-1 filing:

One critical rule: even if you had zero sales in a month or quarter, you must file a nil GSTR-1. Skipping nil returns triggers the same late fee penalties and can block your subsequent filings.

GSTR-1 Filing Deadlines for FY 2026-27

Your filing frequency depends on your aggregate annual turnover in the previous financial year.

Monthly Filers (Turnover Above ₹5 Crore)

If your turnover exceeds ₹5 crore, you must file GSTR-1 every month by the 11th of the following month.

Tax Period | Due Date

April 2026 | 11 May 2026

May 2026 | 11 June 2026

June 2026 | 11 July 2026

July 2026 | 11 August 2026

August 2026 | 11 September 2026

September 2026 | 11 October 2026

October 2026 | 11 November 2026

November 2026 | 11 December 2026

December 2026 | 11 January 2027

January 2027 | 11 February 2027

February 2027 | 11 March 2027

March 2027 | 11 April 2027

Quarterly Filers Under QRMP Scheme (Turnover Up to ₹5 Crore)

Businesses with turnover up to ₹5 crore can opt for the QRMP (Quarterly Return Monthly Payment) scheme. Under QRMP, you file GSTR-1 quarterly by the 13th of the month following the quarter.

Quarter | Tax Period | GSTR-1 Due Date

Q1 | April–June 2026 | 13 July 2026

Q2 | July–September 2026 | 13 October 2026

Q3 | October–December 2026 | 13 January 2027

Q4 | January–March 2027 | 13 April 2027

QRMP filers also get access to the Invoice Furnishing Facility (IFF) - an optional facility to upload B2B invoices for the first two months of each quarter. IFF due date is the 13th of the following month. This helps your B2B buyers claim ITC without waiting for your quarterly filing.

What Changed in 2025-26 That Affects Your GSTR-1 Filing Now

Several CBIC notifications from 2024-25 have fundamentally changed how GSTR-1 works. If you are filing the way you did two years ago, you are exposed.

GSTR-3B Table 3 Is Now Hard-Locked to GSTR-1

Starting July 2025, the outward supply liability in GSTR-3B (Table 3) is auto-populated from GSTR-1 and GSTR-1A data. The figures are locked - you cannot edit them in GSTR-3B.

What this means in practice: if you under-report a sale in GSTR-1, your tax liability in GSTR-3B will be correspondingly lower. When this mismatch surfaces in an audit, you face interest under Section 50 (18% per annum) plus potential penalty proceedings under Section 122 (up to ₹10,000 or the tax amount, whichever is higher).

GSTR-1A: Your Only Correction Window

GSTR-1A was re-introduced via Notification No. 12/2024 dated 10 July 2024. It allows you to add, modify, or delete invoices after filing GSTR-1 but before filing GSTR-3B for the same period.

This is now the only way to correct outward supply data because GSTR-3B is locked. If you discover an error after filing GSTR-3B, you must wait until the next period to amend via the amendment tables in GSTR-1.

3-Year Filing Lock

The GST portal now permanently blocks GSTR-1 filings that are more than three years past their original due date. If you have unfiled returns from 2022-23 or earlier, they are gone - you cannot file them anymore. This also means you cannot claim refunds or make amendments related to those locked periods.

Mandatory Document Series Reporting

From the May 2025 return period, document series reporting in GSTR-1 became mandatory. Every invoice, debit note, and credit note must be reported with its document series. This strengthens audit trails and makes it easier for the department to spot gaps in your invoice numbering.

HSN Code Reporting Requirements

HSN-wise summary reporting is mandatory based on your turnover:

Incorrect HSN codes can trigger notices and affect your buyers' ability to match inward supplies.

E-Invoice Auto-Population

If your business is covered under e-invoicing (currently mandatory for turnover above ₹5 crore), your B2B invoices auto-populate into GSTR-1 from the Invoice Registration Portal (IRP). Editing these auto-populated entries changes the data source flag and may remove IRN-related fields - so avoid editing unless absolutely necessary.

Step-by-Step: How to File GSTR-1

Step 1: Prepare Your Data

Before logging into the GST portal, compile:

Step 2: Log in and Navigate

Go to the GST portal (gst.gov.in), log in with your credentials, navigate to Services > Returns > Returns Dashboard, and select the relevant return period.

Step 3: Enter Invoice Details

Fill in the following tables:

  1. B2B Invoices (Table 4A): Enter GSTIN of each buyer, invoice number, date, taxable value, and tax amounts
  2. B2C Large (Table 5A): Inter-state supplies above ₹2.5 lakh to unregistered persons
  3. B2C Small (Table 7): All other B2C supplies, reported state-wise
  4. Credit/Debit Notes (Table 9): Reference original invoice details
  5. Exports (Table 6A): With or without payment of IGST
  6. Nil Rated/Exempt (Table 8): Nil-rated, exempted, and non-GST outward supplies
  7. HSN Summary (Table 12): HSN-wise summary of outward supplies
  8. Document Details (Table 13): Summary of documents issued during the period

Step 4: Preview and File

Review all tables, ensure invoice values match your books, and file using DSC (Digital Signature Certificate) or EVC (Electronic Verification Code).

Step 5: File GSTR-1A If Needed

If you spot errors after filing GSTR-1, use GSTR-1A to make corrections before you file GSTR-3B. Once GSTR-3B is filed, corrections must wait until the next period.

GSTR-1 Late Fees and Penalties: What Non-Compliance Actually Costs

Late Fee Structure

Scenario | CGST | SGST | Total Per Day | Maximum Cap

GSTR-1 with tax liability | ₹25/day | ₹25/day | ₹50/day | ₹5,000

Nil GSTR-1 | ₹10/day | ₹10/day | ₹20/day | ₹5,000

Interest on Late Payment

If your GSTR-1 delay also means late payment of tax, interest under Section 50 applies at 18% per annum on the net tax liability, calculated from the due date to the date of actual payment.

Cascading Consequences

Late or inaccurate GSTR-1 filing triggers a chain of problems:

Real Penalty Scenarios

Consider a manufacturer in Pune with ₹8 crore turnover who files GSTR-1 three months late. The late fee alone: ₹50 × 90 days = ₹4,500. Add 18% interest on unpaid tax liability - on even ₹5 lakh tax due, that is approximately ₹22,500 in interest. Meanwhile, all buyers who purchased from this manufacturer during those three months could not claim their ITC on time, damaging business relationships.

For a small retailer filing nil returns late by 60 days: ₹20 × 60 = ₹1,200 - for a return that takes five minutes to file.

Common GSTR-1 Filing Mistakes and How to Avoid Them

  1. Wrong GSTIN of buyer: Double-check every buyer GSTIN before uploading. One wrong digit means your buyer's ITC claim fails silently.
  2. Mismatched invoice values: Ensure the taxable value, tax rate, and tax amount in GSTR-1 match your actual invoices. Mismatches trigger notices during reconciliation.
  3. Missing credit/debit notes: Every credit note and debit note must be reported with reference to the original invoice. Missing them skews your and your buyer's tax calculations.
  4. Incorrect place of supply: Getting this wrong converts an intra-state supply to inter-state (or vice versa), changing the tax type from CGST+SGST to IGST. This is a common audit red flag.
  5. Not using GSTR-1A for corrections: Many businesses still try to adjust values directly in GSTR-3B, which is no longer possible. Use GSTR-1A before filing GSTR-3B.
  6. Filing after the 3-year window: If you have pending returns from 2022-23 or earlier, act immediately - the portal will block them permanently.
  7. Ignoring HSN codes: Incorrect or missing HSN codes trigger automated notices from the department.

GSTR-1 Action Checklist for Indian Businesses

Use this checklist every filing period:

Frequently Asked Questions

What happens if I file GSTR-1 late but before filing GSTR-3B?

You will pay the applicable late fee (₹50/day or ₹20/day for nil returns, capped at ₹5,000). However, since GSTR-3B depends on GSTR-1 data, filing GSTR-1 late typically delays your GSTR-3B as well, compounding the late fees and interest.

Can I revise GSTR-1 after filing?

No, GSTR-1 cannot be revised once filed. However, you can use GSTR-1A to make amendments before filing GSTR-3B for the same period. After GSTR-3B is filed, corrections must be made through the amendment tables in the next period's GSTR-1.

Is GSTR-1 mandatory even if I had no sales?

Yes. You must file a nil GSTR-1 even if there were zero outward supplies during the period. Non-filing attracts late fees of ₹20/day (₹10 CGST + ₹10 SGST).

What is the difference between GSTR-1 and GSTR-3B?

GSTR-1 is the detailed statement of outward supplies - it reports every invoice individually. GSTR-3B is the summary return where you declare your total tax liability and claim ITC, and then pay the net tax. GSTR-1 feeds data into GSTR-3B (the liability side is now auto-populated and locked).

How does GSTR-1 affect my buyer's ITC?

Your GSTR-1 data auto-populates your buyer's GSTR-2B. If an invoice is missing or incorrect in your GSTR-1, your buyer cannot see it in their GSTR-2B and therefore cannot claim ITC on that purchase. This is why accurate and timely GSTR-1 filing is critical for the entire supply chain.

What is the QRMP scheme and should I opt for it?

The Quarterly Return Monthly Payment (QRMP) scheme is available for businesses with turnover up to ₹5 crore. Under QRMP, you file GSTR-1 and GSTR-3B quarterly instead of monthly, but pay tax monthly using a challan. It reduces filing effort but you should use IFF to upload B2B invoices monthly so your buyers get timely ITC.

Can I file GSTR-1 for a period older than three years?

No. The GST portal permanently blocks GSTR-1 filings that are more than three years past the original due date. If you have unfiled returns from FY 2022-23 or earlier, they may already be locked out.

Stop Tracking GSTR-1 Deadlines Manually

GSTR-1 is one of over 30 compliance deadlines that Indian businesses must track every month - and missing any single one can trigger penalties, block your operations, or cost your buyers their ITC.

Compliance Radar gives you a complete timeline of every compliance that applies to your business, with real-time alerts when deadlines approach or regulations change. Describe your business once and know exactly what applies to you - no more missed deadlines, no more surprise penalty notices.

Check your compliance posture free at complianceradar.in.