GSTR-1 & GSTR-3B Monthly Filing — Post-Registration Compliance Guide
Post-registration compliance under the Goods and Services Tax regime is a critical responsibility for every registered business in India. As of 2026, the GST ecosystem continues to evolve with digitalization initiatives like e-Invoicing mandates and real-time data matching via GSTR-2A/2B. This guide outlines your mandatory monthly obligations regarding outward supplies declaration (GSTR-1) and tax payment/reconciliation (GSTR-3B). Failure to adhere to these timelines can result in significant financial penalties, interest charges on late payments, and the disallowance of Input Tax Credit by authorities.
Before you start
- Valid GSTIN registered with proper PAN and Aadhaar details updated.
Step-by-step
Prepare Outward Supplies Data for GSTR-1
Gather all sales invoices, debit notes, and credit notes issued during the month. Ensure these are uploaded via the GST Portal or through e-Invoicing (IRN) if your annual turnover exceeds ₹5 crore.
Reconcile Input Tax Credit in GSTR-2A/2B
Download and review your monthly credit ledger from GSTR-2A or 2B. Verify that the ITC claimed matches your supplier's filings to avoid mismatches during scrutiny.
File Monthly Returns via GST Portal
Log in to the official portal and navigate to 'Returns Dashboard'. File GSTR-1 for outward supplies followed by GSTR-3B within the prescribed due dates, ensuring tax liability is paid.
Pay Tax Liability via DSC or OTP
Calculate total output GST minus eligible ITC. Pay the net amount using Challan ITNS-29/28 through authorized banks before midnight of the due date to avoid late fees.
Conduct Quarterly Reconciliation (CMP-01)
While CMP-08 is for annual reconciliation, ensure quarterly checks are done. Review discrepancies between your filed returns and supplier data before filing any correction forms like GSTR-9C.
Address Mismatches via Rectification Forms
If errors are detected post-filing, file the relevant rectification form immediately to update records. Do not ignore minor discrepancies as they can compound into major compliance issues during audits.
Common mistakes to avoid
- Failing to upload e-Invoices with IRN for supplies exceeding ₹50 lakh.
- Ignoring GSTR-2A/2B mismatches which lead to ITC denial by the system.
- Submitting returns after midnight without paying tax, incurring late fees.
Frequently asked questions
What is the due date for monthly GST filing?
For most taxpayers (non-ecommerce), GSTR-1 and GSTR-3B are typically due on the 20th of the following month. However, if the 20th falls on a weekend or holiday, the deadline shifts to the next working day.
Can I file returns late without penalties?
No. Late filing attracts interest at 18% per annum plus late fees of ₹50/day (₹2,000 max) for GSTR-3B and similar charges for GSTR-1.
Is e-Invoicing mandatory in India?
Yes, if your annual turnover exceeds the threshold specified by law. You must generate an IRN (Invoice Reference Number) before issuing invoices to ensure compliance and seamless data flow with GST authorities.
How do I handle discrepancies between GSTR-1 and GSTR-3B?
Ensure that the tax liability paid in GSTR-3B matches your output supplies declared in GSTR-1. Any mismatch can trigger notices from GST officers, so always reconcile before filing.
What happens if I miss a monthly return deadline?
You will face financial penalties including late fees and interest on unpaid tax. Additionally, your Input Tax Credit may be blocked until the default is cleared.
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