GSTR-1 Filing — Due Dates, Format and Step-by-Step Guide FY 2025-26

GSTR-1 Filing — Due Dates, Format and Step-by-Step Guide FY 2025-26

GSTR-1 is the outward supply return filed under Section 37 of the CGST Act 2017. Every B2B invoice you issue flows from your GSTR-1 directly into your customer's GSTR-2B, becoming the legal basis for their Input Tax Credit (ITC) claim. In FY 2026-27, with CBIC tightening e-invoice reconciliation at the GSTN level and making HSN summary mandatory at finer digit levels, a wrong or late GSTR-1 no longer just hurts you — it breaks ITC for every buyer on those invoices, damaging your commercial relationships and inviting scrutiny notices for both parties. Get the basics right here before filing another return.

Why GSTR-1 Is the Cornerstone of Your GST Chain

Every return you file downstream — GSTR-3B for tax payment, GSTR-9 for annual reconciliation — is validated against what you declared in GSTR-1. Your buyers cannot claim ITC until your invoices appear in their auto-populated GSTR-2B, which is generated from your GSTR-1 data. A supplier who habitually misses the 11th creates a working-capital problem for their corporate buyers who monitor 2B mismatches on the 14th every month.

There is a second, increasingly important dimension. Lenders and investors now routinely pull GSTIN-level data from the GST portal during due diligence. A consistent, clean GSTR-1 filing history is treated as revenue corroboration. A company with irregular filings or large amendments will face uncomfortable questions during a credit appraisal or funding round that a clean filing history would have pre-empted entirely.

Due Dates for GSTR-1 in FY 2026-27

Monthly Filers

If your aggregate turnover in the preceding financial year exceeded Rs. 5 crore, or if you opted out of QRMP, you file GSTR-1 monthly. The due date is the 11th of the following month.

QRMP Scheme Filers

Taxpayers with aggregate turnover up to Rs. 5 crore in FY 2025-26 are eligible for the Quarterly Return Monthly Payment (QRMP) scheme. Under QRMP, you pay tax monthly using Form PMT-06 but file GSTR-1 only once per quarter by the 13th of the month after the quarter ends.

IFF: The Monthly Upload Window for QRMP Filers

QRMP filers have an optional tool called the Invoice Furnishing Facility (IFF). During the first two months of each quarter, you can upload B2B invoices (Table 4 data only) through IFF by the 13th of the following month. The third-month invoices, plus all other tables including B2C and HSN summary, go into the quarterly GSTR-1.

Why use IFF at all? Your B2B customers receive ITC on an invoice only after it appears in their GSTR-2B. If you skip IFF, all three months of invoices only hit 2B after the quarterly GSTR-1 is filed — meaning buyers wait up to 90 days for ITC they need monthly. Most mid-size buyers will stop purchasing from a QRMP supplier who does not use IFF diligently.

Late Fee: The Real Cost of Missing the 11th

Under Section 47 of the CGST Act, read with current CBIC notifications, the late fee for GSTR-1 is:

• Rs. 50 per day (Rs. 25 CGST + Rs. 25 SGST) for returns with outward supply data
• Rs. 20 per day (Rs. 10 CGST + Rs. 10 SGST) for nil returns
• Maximum cap: Rs. 10,000 per return (as amended by Finance Act 2022), subject to the figures as finally notified per applicable CBIC notifications for FY 2026-27

A concrete example: if you file the April 2026 GSTR-1 on 26 May 2026 instead of 11 May, that is a 15-day delay at Rs. 50/day = Rs. 750 in total late fee (Rs. 375 each under CGST and SGST). Trivial for a one-off, but multiply that by 12 months and it compounds — and CBIC can still issue notices for systemic late filing independent of the fee paid.

GSTR-1 Format: Table-by-Table Breakdown

GSTR-1 contains 13 tables. You do not fill every table every period, but you must understand which applies to each transaction type.

Table 4 — B2B Taxable Supplies

The most critical table. Every invoice issued to a registered person (B2B) goes here: GSTIN of recipient, invoice number, date, place of supply, total invoice value, taxable value, and IGST/CGST/SGST breakup. This data auto-populates the buyer's GSTR-2B. An error in GSTIN means the invoice goes to the wrong GSTIN or floats unmatched — the buyer loses ITC until you amend.

Table 5 — B2C Inter-State Large Invoices

B2C (unregistered buyer) inter-state invoices above Rs. 2.5 lakh are reported here at invoice level, with state-wise breakup. This feeds the TCS reconciliation and is used for cess calculation.

Tables 6A, 6B and 6C — Exports, SEZ and Deemed Exports

• 6A: Export supplies (with or without payment of IGST). Choose "with payment" for LUT-free exports; "without payment" if you are a LUT holder. Shipping Bill number and date are mandatory fields.
• 6B: Supplies to SEZ units and SEZ developers, with or without IGST.
• 6C: Deemed exports.

Misclassifying an SEZ supply as regular B2B, or reporting an export as B2C, is a common error that attracts IGST refund complications and notices from the jurisdictional officer.

Table 7 — B2C Small Supplies and Intra-State B2C

Aggregate (rate-wise, state-wise) reporting of unregistered buyer invoices not covered in Table 5. You do not report these at invoice level — it is a summary entry.

Tables 9A, 9B and 9C — Amendments

Corrections to invoices, debit notes, and credit notes reported in earlier periods are handled here, not by editing the original period's return. Table 9A amends B2B invoices; 9B amends export invoices; 9C captures amended credit/debit notes. You must quote the original invoice number and GSTIN alongside the corrected values.

Table 11 — Advances Received and Adjusted

Advances received from unregistered persons on which GST is payable must be declared here. When the invoice is raised in a later period, the advance is adjusted. Many taxpayers skip Table 11 entirely because they do not issue advance receipts — that is acceptable if no advance was actually received — but omitting it when advances exist creates a GST liability gap.

Table 12 — HSN Summary

From 1 April 2022 (effective for FY 2026-27 onwards), HSN-level summary reporting is mandatory:

• Aggregate turnover above Rs. 5 crore: 6-digit HSN mandatory
• Aggregate turnover up to Rs. 5 crore: 4-digit HSN mandatory for B2B supplies; optional for B2C

Each HSN row must show: HSN code, description, UQC (Unit of Quantity Code), quantity, total value, and tax-wise breakup. GSTN now cross-checks HSN summary totals against the invoice-level data in Tables 4–7 and against your e-invoice IRN data. A mismatch flags the return and can generate a query notice.

E-Invoice and IRN: The Layer Above GSTR-1

If your aggregate turnover exceeds Rs. 5 crore (the current CBIC-notified threshold), every B2B invoice, debit note and credit note must be generated through the Invoice Registration Portal (IRP) before it is issued to your buyer. The IRP assigns an Invoice Reference Number (IRN) and a QR code.

The GST portal then auto-populates IRN-linked invoices into your GSTR-1 as you go. By the time you sit to file, most of your Table 4 data is already pre-filled from the IRP. Your job shifts from data entry to review and reconciliation — ensuring every IRN that was generated has landed correctly in the right GSTR-1 period and in the right table.

What breaks this:

• Generating an IRN in March 2027 but the accounting team manually reporting it in April 2027's GSTR-1 due to a cut-off confusion
• Cancelling an IRN but not ensuring the corresponding invoice has been removed from the GSTR-1 summary
• Partial upload of bulk invoices — 487 IRNs generated, 481 reflected in GSTR-1; 6 slip through

Run an IRN-to-GSTR-1 reconciliation at least fortnightly using the download available on the GST portal under the e-invoice section. Do not wait for the 10th of the month to discover a gap.

Step-by-Step GSTR-1 Filing on the GST Portal

Follow this sequence exactly. Deviating from it — particularly filing GSTR-3B before GSTR-1 — breaks the sequential dependency the portal enforces.

1. Log in to unknown node → Services → Returns → Returns Dashboard.
2. Select the Financial Year (2026-27) and Tax Period (e.g., April 2026). Choose GSTR-1 and click Prepare Online (manual entry) or Upload JSON (from your accounting software such as Tally, Zoho Books, or ERP).
3. If uploading JSON, ensure the file is in the GSTN-prescribed schema. Validation errors will appear table-by-table; fix them before proceeding.
4. Open Table 4 and verify all B2B invoices are populated correctly. For e-invoice filers, most entries will be pre-filled — review each entry for correct place of supply and tax type (IGST vs. CGST+SGST).
5. Fill Tables 5, 6A/6B/6C, 7 as applicable for your transaction types.
6. Add debit notes and credit notes in the respective fields within Tables 4 and 6 (amendments to current period) or in Tables 9A/9B/9C (amendments to prior periods).
7. Complete Table 12 (HSN Summary) at the required digit level. The portal validates whether the taxable values and tax amounts in the HSN rows sum to the totals declared in the invoice tables above.
8. Click Generate GSTR-1 Summary. Review the summary screen — it shows totals by table and by tax type. Compare this against your internal sales register.
9. If discrepancies exist, edit before submitting. Once Submit is clicked, data is frozen — you can only amend via Table 9 in a future period.
10. File using DSC (Digital Signature Certificate) for companies and LLPs, or EVC (Electronic Verification Code sent to the registered mobile) for proprietorships and partnerships.
11. Download the filed return acknowledgement (ARN) immediately and save it in your compliance record. The ARN is your proof of timely filing.

QRMP and IFF Filing — The Practical Workflow

If you are a QRMP filer, your workflow for Q1 (April–June 2026) should look like this:

• By 13 May 2026: File IFF for April invoices (Table 4 B2B data only). Your April buyers get ITC in May's GSTR-2B.
• Pay PMT-06 by 25 May 2026 for April's tax.
• By 13 June 2026: File IFF for May invoices. May buyers get ITC in June 2B.
• Pay PMT-06 by 25 June 2026 for May's tax.
• By 13 July 2026: File full GSTR-1 for Q1 — includes June invoices (Table 4), plus all B2C, export, HSN summary, and any amendments not uploaded via IFF.

Critical rule: Invoices uploaded in IFF do not need to be re-entered in the quarterly GSTR-1 — they carry forward automatically. Enter only the third-month invoices and the remaining tables.

Common Mistakes That Break Your Customers' ITC

These are the errors seen repeatedly in practice, each with its downstream consequence:

• Wrong GSTIN of the recipient. The invoice goes to the wrong party's 2B. Your actual customer sees no ITC; a stranger gets an erroneous credit. Fix: verify GSTIN from the Search Taxpayer feature on the GST portal before billing, not after.
• Invoice number mismatch between IRN and GSTR-1. If your accounting software truncates long invoice numbers differently from what was sent to IRP, the portal's cross-validation raises a flag. Standardise your invoice numbering format and lock it for the year.
• Exports reported in Table 4 (B2B) instead of Table 6A. An export invoice carrying GSTIN of a foreign buyer (not valid Indian GSTIN) that lands in Table 4 causes a validation failure. Exports must always go to Table 6A.
• Credit notes omitted or delayed. If you issue a credit note in April but report it only in June's GSTR-1, your buyer's GSTR-2B shows the full invoice in April and the reversal only in June — causing a 2B mismatch flag in April's reconciliation. Report credit notes in the same period they are issued wherever possible.
• HSN codes copy-pasted from last year without review. HSN classifications for goods and services are updated periodically. A wrong 8-digit HSN on a pharmaceutical product, for example, can create a mismatch against the e-way bill and e-invoice data.
• Filing GSTR-3B before GSTR-1 for the same period. The GST portal now enforces GSTR-1 first for monthly filers in most scenarios. But even where the portal allows it, filing 3B before 1 creates reconciliation gaps that the audit trail will expose. Always file GSTR-1 before GSTR-3B.

Amendments in GSTR-1: What the Time Limit Actually Means

You cannot edit a GSTR-1 once filed. Corrections happen through Tables 9A, 9B and 9C of a subsequent period's GSTR-1. However, Section 37(3) of the CGST Act places a hard boundary: you can amend GSTR-1 data only up to the earlier of:

1. The 30th November of the financial year following the tax year in which the original supply was made; or
2. The date of filing the Annual Return (GSTR-9) for that year.

For FY 2025-26, the amendment window closes on 30 November 2026 (or GSTR-9 filing, whichever is earlier). After that, the error becomes permanent in the GST database. The only downstream route is to address it in GSTR-9 with appropriate explanatory reconciliation.

Practical implication: If your March 2026 GSTR-1 had a wrong GSTIN on a Rs. 12 lakh invoice, you have until 30 November 2026 to correct it via Table 9A in any subsequent GSTR-1 (e.g., April 2026 or later). Do not sit on corrections — the window feels wide until it suddenly is not.

Worked Example: Monthly GSTR-1 for a Mid-Size Manufacturer

Scenario: Prakash Auto Components Pvt Ltd, Pune. Aggregate turnover Rs. 9.6 crore in FY 2025-26 (monthly filer, e-invoice applicable).

April 2026 transactions:

• 42 B2B invoices to registered dealers across Maharashtra and Gujarat — total taxable value Rs. 74 lakh, IGST Rs. 11.1 lakh (inter-state), CGST+SGST Rs. 2.22 lakh (intra-state)
• 8 invoices to unregistered retail buyers in Maharashtra — total value Rs. 3.2 lakh (B2C intra-state, below Rs. 2.5 lakh each)
• 2 export invoices to a UAE buyer under LUT — FOB value Rs. 6 lakh, no IGST paid
• 1 credit note against a March invoice for Rs. 45,000 (goods returned)

What goes where:

• 42 B2B invoices → Table 4 (pre-populated from IRP IRNs; cross-check all 42 IRNs are present)
• 8 retail invoices → Table 7 (aggregate, rate-wise)
• 2 export invoices → Table 6A (without payment of IGST, LUT number entered)
• Credit note on March invoice → Table 9B (amendment to prior-period export invoice, if the original was in 6A) or Table 9A (if against a B2B invoice)

HSN Summary — Table 12: Since annual turnover exceeds Rs. 5 crore, 6-digit HSN is mandatory. For HSN 870899 (auto parts), the entry shows: taxable value Rs. 77.2 lakh (combined B2B + B2C), IGST Rs. 11.1 lakh, CGST Rs. 1.11 lakh, SGST Rs. 1.11 lakh.

Late fee exposure: The finance team missed the 11 May 2026 deadline and filed on 21 May 2026 — 10 days late. Late fee = Rs. 50/day × 10 days = Rs. 500 total (Rs. 250 CGST + Rs. 250 SGST). Small amount, but the delay meant 42 buyers could not see these invoices in their May 2B — creating unnecessary reconciliation queries.

Pitfalls to Avoid: The GSTR-1 Checklist Before You Hit Submit

Before filing each return, run through this five-point check:

1. Count check: Total invoices in accounting software vs. total invoices in GSTR-1 (including pre-filled IRN data). They must match.
2. Tax amount check: Total IGST / CGST / SGST in GSTR-1 summary vs. your sales register. A variance of even Rs. 500 warrants investigation before filing.
3. GSTIN validation: For the top 10 B2B buyers by value, search their GSTIN on the portal to confirm active status. Invoices to cancelled GSTINs do not generate valid ITC.
4. HSN totals tie-back: The sum of taxable values in Table 12 must equal the sum of Tables 4+5+6+7. If they differ, the portal will flag it.
5. Amendment carry-forward: Any correction identified after last month's filing must be entered in the current period's Table 9 rows before filing. Do not forget them.

Key Takeaways

• Monthly filers: GSTR-1 due by the 11th of the following month; QRMP quarterly filers by the 13th after quarter end.
• QRMP + IFF: Upload B2B invoices in IFF by the 13th of months 1 and 2 of each quarter so your buyers do not wait 90 days for ITC.
• Table 4 accuracy is non-negotiable: One wrong GSTIN breaks a buyer's ITC claim completely, and the fix takes at least one additional month via Table 9A.
• E-invoice filers: Run a fortnightly IRN-to-GSTR-1 reconciliation to catch slipped invoices before the filing date.
• HSN summary: If turnover exceeds Rs. 5 crore, 6-digit HSN is mandatory in Table 12 from FY 2026-27; totals must reconcile to your invoice tables.
• Amendment window: Section 37 gives you until 30 November 2026 (or GSTR-9 filing date) to correct FY 2025-26 errors — act monthly, not in a year-end panic.
• GSTR-1 before GSTR-3B: Always file in this sequence. Reversing it creates audit trail inconsistencies that take a departmental response letter to explain.