GSTR-1 & GSTR-3B Monthly Filing — Post-Registration Compliance Guide
The moment your GSTIN is approved, the compliance clock starts running — GSTR-1 (outward supplies) and GSTR-3B (summary return with tax payment) become due every month regardless of whether you have made a single sale yet. Many first-time registrants underestimate this and miss their first filing cycle entirely, which is a costly way to learn the routine. As of 2026, the GST ecosystem is largely automated end to end: e-Invoicing feeds directly into your GSTR-1 draft if your turnover crosses the mandatory threshold, and the Invoice Management System (IMS) means your buyers act on every invoice you report, which shapes their GSTR-2B and your own reputation as a supplier. This guide sets up the recurring monthly workflow you need immediately after registration — from your first nil return through steady-state filing, reconciliation, and payment — so you are never caught off guard by a due date. Interest and late fees apply from day one of default, so the discipline established in your first few filing cycles matters more than it might seem.
Before you start
- Active GSTIN with PAN, Aadhaar (for individual proprietors/partners), and bank account details verified on the GST portal
- GST portal login credentials created and first-time password reset completed
- Digital Signature Certificate (Class 3, for companies and LLPs) or a registered mobile/email for EVC-based authentication
- A sales invoice format finalized that captures GSTIN, place of supply, and HSN/SAC codes correctly from the first invoice issued
- Purchase invoice register set up to track vendor GSTINs for Input Tax Credit (ITC) matching
- Bank account enabled for net banking or NEFT/RTGS to pay GST challans
- Decision made on filing frequency — monthly, or the Quarterly Return Monthly Payment (QRMP) scheme if aggregate turnover is up to ₹5 crore
- Accounting software or a GST offline utility set up to generate invoice-wise GSTR-1 data
Step-by-step
Confirm Your Filing Frequency and First Return Period
Check your GST portal dashboard to see whether you have been defaulted to monthly filing or the QRMP scheme (available if aggregate turnover is up to ₹5 crore). Your first return period starts from the effective date of registration, not the date of approval — even a gap with zero sales still requires a nil return for that period.
- If eligible for QRMP, you can opt in or out for the upcoming quarter within the window the portal allows.
- Note your due dates: GSTR-1 is generally due by the 11th of the following month (13th for QRMP filers using the Invoice Furnishing Facility), and GSTR-3B is generally due by the 20th (staggered dates around the 22nd/24th apply to some QRMP taxpayers by state group).
Set Up Your Sales Invoice and Classification Workflow
From your very first invoice, classify sales correctly: B2B (registered buyers), B2C large, B2C small (consolidated), exports, SEZ supplies, and nil-rated/exempt supplies. Getting this classification right from day one avoids a backlog of reclassification work later.
- If your turnover crosses the mandatory e-Invoicing threshold, you must generate an IRN (Invoice Reference Number) before issuing the invoice — check the current threshold on the official e-invoice portal, as it has been lowered progressively over recent years.
- Below the threshold, e-Invoicing is optional but many businesses still adopt it voluntarily for cleaner reconciliation.
File Your First GSTR-1 (Even If Nil)
Log in to the GST portal, go to Returns Dashboard, select the tax period, and open GSTR-1. If there were no outward supplies in your first period, file a nil return rather than skipping it — a missed nil filing still triggers late fees and can block subsequent filings. Eligible taxpayers can also file a nil GSTR-1 via the SMS facility, though it's worth verifying the current SMS format on the official portal before relying on it.
Register for and Monitor the Invoice Management System (IMS)
IMS is where your buyers accept, reject, or leave pending each invoice you report in GSTR-1. Their action determines whether it flows into their GSTR-2B for ITC. As a newly registered supplier, get into the habit of checking IMS after every GSTR-1 filing so disputes are caught before they harden into ITC mismatches with your buyers.
Download and Reconcile GSTR-2B for Your Own Purchases
Download the auto-generated GSTR-2B for the period, typically available a few days after the GSTR-1 due date. Match it against your purchase register before claiming any Input Tax Credit.
- Claim ITC only for invoices that actually appear in GSTR-2B — this is now the primary statement the department relies on for ITC eligibility, not GSTR-2A.
- If a vendor hasn't filed their return, the credit simply won't show up yet; follow up with them rather than claiming it unilaterally.
Compute Net Tax Liability and Generate the Payment Challan
Calculate output tax from your filed GSTR-1, net off eligible ITC from GSTR-2B, and compute the IGST/CGST/SGST split. Generate Form PMT-06 on the portal for the net cash amount payable and pay via net banking, NEFT/RTGS, or over-the-counter for amounts within the permitted limit. Reverse charge mechanism (RCM) liability, if applicable, must be paid in cash and cannot be set off against ITC on the same transaction.
File GSTR-3B by the Due Date
Open GSTR-3B for the period. Review the figures auto-populated from your filed GSTR-1 and GSTR-2B — these fields are largely locked for direct editing under current portal rules, so any correction to outward-supply data should be routed through GSTR-1A before you file 3B, not typed over manually. Offset the liability against your Electronic Cash and Credit Ledger balances, then submit and file using DSC or EVC.
Reconcile GSTR-1 and GSTR-3B Figures Against Each Other
Before closing out the month, confirm that the outward-supply liability declared in GSTR-3B is consistent with what you reported in GSTR-1 for the same period. A material gap between the two — especially 3B understating liability relative to 1 — is a common trigger for a departmental notice, since it reads as a deliberate mismatch even when it is a genuine error.
Archive Filing Acknowledgments and Set a Recurring Compliance Calendar
Download and store the ARN (Application Reference Number) for both returns and the payment challan for each period. Set calendar reminders a few days ahead of each due date rather than relying on portal notifications alone, since a missed reminder in the first few months is the most common way new registrants accumulate late fees.
Plan for Annual Return Obligations Alongside Monthly Filing
Monthly GSTR-1/3B filing does not replace the annual return (GSTR-9) or reconciliation statement (GSTR-9C, where applicable by turnover) due after the financial year closes. Keep monthly working papers organized through the year so the annual reconciliation isn't a scramble — this is one of the most common gaps for businesses in their first year of registration.
Common mistakes to avoid
- Assuming no sales means no filing obligation — a nil GSTR-1 and GSTR-3B must still be filed for every period after registration, or late fees accrue regardless.
- Filing GSTR-1 after its due date — this delays your buyers' ITC through GSTR-2B/IMS and attracts a late fee that compounds daily up to a cap; confirm the current fee schedule on the portal rather than assuming it is fixed year to year.
- Claiming ITC based on vendor invoices or GSTR-2A instead of the auto-drafted GSTR-2B, which is the statement the department now relies on for ITC eligibility.
- Treating GSTR-3B's auto-populated figures as freely editable — corrections to outward-supply data generally need to go through GSTR-1A rather than a manual overwrite in 3B.
- Not registering for or checking the Invoice Management System, so buyer rejections or pending flags go unnoticed until they surface as ITC disputes.
- Skipping e-Invoicing once turnover crosses the mandatory threshold — non-compliant invoices can be treated as not having been issued at all for GST purposes, jeopardizing the buyer's ITC.
- Paying the tax challan but forgetting to actually file GSTR-3B — payment alone does not complete the return; the ARN is generated only on filing.
- Letting the first few months' filings pile up because the business is small — late fees and interest accrue per return and per day, so a backlog compounds quickly rather than being a one-time catch-up cost.
Frequently asked questions
When does my monthly GST filing obligation start after registration?
From the effective date of registration shown on your GST certificate — not the date the certificate was approved or issued. If that date falls mid-month, you still owe a return (nil, if there were no supplies) for that first partial period.
What is the due date for monthly GST filing?
GSTR-1 is generally due by the 11th of the following month (the 13th for QRMP filers using the Invoice Furnishing Facility). GSTR-3B is generally due by the 20th for monthly filers, with staggered dates around the 22nd or 24th for some QRMP taxpayers depending on their state group. Always check the portal's return calendar for your specific category, as staggered dates and exceptions apply.
Am I eligible for the QRMP scheme instead of monthly filing?
The Quarterly Return Monthly Payment scheme is available to taxpayers with aggregate annual turnover up to ₹5 crore. It lets you file GSTR-1 and GSTR-3B quarterly while still paying tax monthly through a fixed-sum or self-assessed challan — it reduces filing frequency but not the monthly payment discipline.
Can I file returns late without penalties?
No. Late filing attracts interest on the unpaid tax (18% per annum, calculated from the day after the due date) plus a per-day late fee on GSTR-3B and GSTR-1 separately, subject to a maximum cap — confirm the current fee amounts on the GST portal, as these have been revised in the past and may change again.
Is e-Invoicing mandatory for a newly registered business?
Only once your aggregate turnover (across any financial year since 2017-18) crosses the mandatory threshold currently prescribed by the GST Council — confirm the current figure on the official e-invoice portal, since it has been lowered in phases. Below that threshold, e-Invoicing is optional.
How do I handle discrepancies between GSTR-1 and GSTR-3B?
Ensure the tax liability paid in GSTR-3B matches the outward supplies declared in GSTR-1 for the same period. If a correction is needed after GSTR-1 is filed but before GSTR-3B is due, file GSTR-1A rather than adjusting 3B manually. A persistent, unexplained mismatch is a common trigger for a departmental notice.
What happens if I miss a monthly return deadline?
You face a late fee per return plus interest on any unpaid tax, and your Input Tax Credit for the period may effectively be delayed since a late GSTR-1 also delays your buyers' GSTR-2B. Persistent default can also affect your GST compliance rating and trigger scrutiny.
What is GSTR-2B and how is it different from GSTR-2A?
GSTR-2B is a static, auto-drafted monthly statement of eligible ITC generated once for each period, and it is now the primary reference the department expects you to reconcile against. GSTR-2A is a dynamic, continuously updated ledger reflecting supplier filings as they happen — useful for cross-checking, but GSTR-2B is the authoritative figure for claiming credit.
Do I need a Digital Signature Certificate to file GST returns after registration?
Companies and LLPs are generally required to file using a Class 3 DSC. Proprietorships and most other entity types can typically authenticate using an Electronic Verification Code sent to the registered mobile and email instead — confirm the requirement applicable to your entity type on the portal.
Can I amend a GSTR-1 I already filed?
Yes. Minor invoice-level corrections can be made in the amendment tables of a later month's GSTR-1, and GSTR-1A allows in-period corrections after the original GSTR-1 is filed but before GSTR-3B for that same period is filed.
Does monthly filing cover my annual GST obligations too?
No. Monthly or quarterly GSTR-1/3B filings are separate from the annual return (GSTR-9) and, where applicable by turnover, the reconciliation statement (GSTR-9C) due after the financial year ends. Keep your monthly reconciliation records organized through the year so the annual filing is a compilation exercise, not a fresh reconstruction.
What should a newly registered business do in its very first filing month if there are no sales yet?
File a nil GSTR-1 and nil GSTR-3B for that period rather than assuming no obligation exists. Nil returns are quick to file (including via SMS for eligible taxpayers) and skipping them is one of the most common — and most easily avoided — compliance lapses for new registrants.
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