Documents Required for GSTR-1 & GSTR-3B Monthly Filing in India
Accurate monthly GST filing is the backbone of a compliant business in India, and the discipline of assembling the right paperwork before you log into the GST portal is what separates a clean filing from one that triggers a notice. This guide sets out exactly what documents and data points you need to have on hand before preparing GSTR-1 (outward supplies) and GSTR-3B (the summary return with tax payment), whether you file monthly or fall under the QRMP quarterly scheme with monthly tax payment. Missing even a single invoice, an unreconciled e-way bill, or a mismatched HSN code can lead to notices, interest under Section 50 of the CGST Act, and blocked Input Tax Credit. The process below assumes a regular taxpayer registered under GST who is not opting for the composition scheme, and it applies equally to businesses filing on their own or through a professional. Keep your books updated in real time rather than reconstructing a month's transactions at the deadline — it is the single biggest driver of filing accuracy.
Before you start
- Ensure your GSTIN is active and linked with valid PAN/Aadhaar details, and that your registration has not been suspended for non-filing.
- Complete Aadhaar authentication or e-KYC on the GST portal if not already done, as this affects refund processing and certain filing privileges.
- Have your GST portal login credentials and, for companies/LLPs, a valid Digital Signature Certificate (DSC) ready for return verification.
- Confirm whether you are on the monthly filing scheme or the QRMP (Quarterly Return Monthly Payment) scheme, since document cut-off dates differ.
- Maintain a day-to-day sales and purchase register (manual or accounting-software based) so invoice data does not need to be reconstructed at month-end.
- Keep your e-invoicing setup current if your aggregate annual turnover exceeds the applicable e-invoicing threshold, since IRN-generated invoices auto-populate GSTR-1.
- Reconcile your bank statement and cash book for the month so tax payments and any additional cash ledger deposits can be verified.
- Set up a system to download GSTR-2B as soon as it is generated each month, since it is the primary reference for ITC claims.
Step-by-step
Gather all outward supply invoices
Collect every tax invoice issued during the month — B2B, B2C large (interstate invoices above the applicable threshold), B2C small, and export invoices. Each B2B invoice must carry the recipient's correct GSTIN; a wrong or missing GSTIN is one of the most common reasons a buyer's ITC claim fails to match in GSTR-2B.
If your turnover crosses the e-invoicing threshold applicable to your category, confirm that every B2B invoice has a valid IRN (Invoice Reference Number) and QR code generated through the Invoice Registration Portal before it is reported in GSTR-1 — most such invoices now auto-populate into GSTR-1 from the e-invoice system, but you should still verify the auto-drafted data against your books.
Collect debit notes, credit notes, and amendments
Pull together all credit notes and debit notes issued during the month, along with details of any earlier-period invoices that need amendment. These are reported separately in GSTR-1 and directly affect your net outward tax liability, so an omitted credit note can overstate your GST payable.
Compile HSN/SAC-wise summary of supplies
Prepare a summary of outward supplies classified by HSN (goods) or SAC (services) code, along with quantity and taxable value. Reporting requirements for the number of HSN digits vary with turnover slabs, so confirm the digit requirement applicable to your turnover for the current filing period before finalizing this summary.
Extract e-way bill records for goods movement
If your business moves goods, download the e-way bills generated during the month, including challan references and vehicle details. Cross-check these against your outward supply invoices — a mismatch between e-way bill value and invoice value is a common trigger for scrutiny.
Download and reconcile GSTR-2B
Download the auto-generated GSTR-2B statement for the period, which lists eligible and ineligible ITC based on your suppliers' filings. Match every line against your purchase register.
- Flag invoices your suppliers have not yet uploaded — you cannot claim ITC on these until they appear in GSTR-2B.
- Identify ineligible credits under Section 17(5) (e.g., motor vehicles for personal use, employee welfare expenses in some cases) and exclude them from your claim.
- Note any duplicate or double-counted entries before finalizing the ITC figure for GSTR-3B.
Prepare the ITC reconciliation working
Build a working paper that reconciles ITC as per your books, ITC as per GSTR-2B, and ITC actually claimed in GSTR-3B. This working paper is your primary defense document if the department later raises a mismatch notice, so retain it along with supporting invoices for the statutory record-retention period.
Verify RCM (Reverse Charge Mechanism) liabilities
List any inward supplies during the month that attract reverse charge — for example, certain services from unregistered persons or specified categories notified under RCM. Compute the tax payable on these separately, since RCM liability must be discharged in cash and cannot be offset against ITC balance, though the tax so paid can itself become eligible ITC in most cases.
Compute advance tax liability and verify challan payments
Calculate the net tax payable after adjusting eligible ITC, and generate the challan (Form GST PMT-06) for any balance payable in cash. Verify that earlier deposits into your electronic cash ledger are correctly reflected before you finalize GSTR-3B, since an unreconciled ledger balance can lead to short payment and consequent interest.
Verify export and SEZ documentation
For exporters, gather shipping bills, Bill of Lading or Airway Bill details, and Letter of Undertaking (LUT) references so zero-rated supplies are reported correctly in GSTR-1. Ensure the LUT for the relevant financial year is active on the portal, since an expired LUT can force exports to be reported as taxable supplies with tax payment and subsequent refund claim.
Match GSTR-1 with GSTR-3B before filing
Compare the auto-populated summary in GSTR-3B (Table 3.1 outward supplies) against your finalized GSTR-1 data. Persistent mismatches between the two returns are a recurring trigger for automated departmental scrutiny notices, so resolve differences before submission rather than after.
File returns and retain acknowledgment records
File GSTR-1 first, then GSTR-3B, using DSC or EVC (Electronic Verification Code) as applicable to your entity type. Download and archive the filed return copies, acknowledgment reference numbers (ARNs), and challan receipts — these form part of your statutory books of account and are needed for any future assessment or audit.
Common mistakes to avoid
- Reporting outward supplies in GSTR-1 without verifying the recipient's GSTIN, which causes the buyer's ITC to fail to reflect in their GSTR-2B.
- Claiming ITC in GSTR-3B that has not yet appeared in GSTR-2B, which can lead to a mismatch notice and reversal with interest.
- Missing the reverse charge liability on notified inward supplies and only discovering the gap during an annual reconciliation.
- Filing GSTR-3B without reconciling the auto-populated figures against the finalized GSTR-1 data for the same period.
- Letting an export LUT lapse and continuing to report exports as zero-rated without a valid LUT on record.
- Treating e-way bill and invoice value inconsistently, especially when discounts or free supplies are involved.
- Ignoring credit notes issued in a later period, which understates the tax adjustment and overstates liability.
- Assuming due dates are fixed calendar dates without checking whether your state falls under a staggered filing group or the QRMP scheme.
Frequently asked questions
What is the due date for filing GSTR-1 and GSTR-3B under monthly filing?
For regular monthly filers, GSTR-1 is generally due by the 11th of the following month and GSTR-3B by the 20th, though exact dates and any staggered schedules by state or turnover category can change — always confirm the current due dates on the GST portal before filing rather than relying on a fixed rule of thumb.
Can I file GSTR-1 and GSTR-3B independently of each other?
Yes, they are separate filings, but GSTR-3B's outward supply summary is auto-drafted from GSTR-1 data, so it is best practice to finalize and file GSTR-1 first and reconcile before submitting GSTR-3B. Filing them with inconsistent figures is a common cause of scrutiny notices.
What happens if I miss claiming ITC in the month it becomes eligible in GSTR-2B?
ITC can generally still be claimed in a later return, but only within the statutory time limit prescribed under the CGST Act for claiming credit for a financial year (commonly tied to the November return of the following year or the annual return date, whichever is earlier). Confirm the current time limit with your GST advisor before assuming a claim is still open.
Do I need e-invoicing before my invoices can be reported in GSTR-1?
E-invoicing (IRN generation) is mandatory only for B2B invoices once your aggregate annual turnover crosses the notified threshold, which has been lowered progressively in recent years. If you are below the threshold, you can report invoices directly in GSTR-1 without an IRN. Confirm the current applicable threshold, as it is subject to periodic revision by notification.
What is the QRMP scheme and how does it change my documentation?
Under QRMP, eligible small taxpayers (typically those with turnover up to the notified limit, currently ₹5 crore in the preceding year) file GSTR-1 and GSTR-3B quarterly but pay estimated tax monthly using a simplified challan. You still need monthly sales data to compute the tax payment accurately, even though the detailed return itself is filed quarterly.
What documents should I retain after filing, and for how long?
Retain filed return copies, ARNs, tax invoices, debit/credit notes, e-way bills, ITC reconciliation workings, and payment challans. GST law requires retention of books of account and records for a minimum period after the due date of the annual return for the relevant year — confirm the exact retention period applicable to your case, as it can extend further if litigation or audit proceedings are pending.
What happens if my supplier does not upload their invoice and I have already claimed ITC?
If ITC claimed does not match GSTR-2B, the department may issue an automated intimation seeking reversal with interest. It is safer to only claim ITC once it reflects in GSTR-2B, and to follow up with non-compliant suppliers promptly rather than carrying an unmatched credit.
Is there a late fee for missing the GSTR-1 or GSTR-3B due date?
Yes, late filing attracts a late fee per day of delay (subject to a cap), in addition to interest on any tax paid late. The exact late fee slabs have been revised by the government in the past, so confirm the current schedule rather than relying on an old figure.
Can a nil return be filed if there were no transactions during the month?
Yes, a nil GSTR-1 and nil GSTR-3B must still be filed if you are registered and had no outward or inward transactions during the period; nil filing can also be done via SMS for GSTR-3B in eligible cases. Skipping a nil filing still attracts late fees and can affect your compliance rating.
How does reverse charge tax paid during the month get treated for ITC?
Tax paid under reverse charge is generally eligible to be claimed as ITC in the same or a subsequent return, provided the underlying supply is used for business purposes and is not in the blocked-credit category under Section 17(5). It must be paid in cash first — it cannot be set off against existing ITC balance.
What should I do if I discover an error in a GSTR-1 already filed for a past month?
Most errors can be corrected through amendment tables in a subsequent month's GSTR-1 rather than by revising the original return, since GST does not currently allow revision of a filed return. Keep clear documentation of the original error and the correcting entry for audit trail purposes.
Do exporters need any additional document besides the standard GSTR filings?
Exporters filing under LUT (without payment of tax) should keep the LUT acknowledgment, shipping bills, and export invoices on file, and periodically verify that export data reported in GSTR-1 matches shipping bill data on the customs (ICEGATE) system, since discrepancies between the two can delay any related refund processing.
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