GSTR-1 vs GSTR-3B: Differences, Due Dates, and Filing Sequence

Every GST-registered business in India files two core returns each tax period: GSTR-1 and GSTR-3B. Both go to the same portal (gst.gov.in), both carry penalties for late filing, and both deal with your sales data. Yet they serve completely different purposes, and confusing what goes where is one of the fastest ways to trigger a mismatch notice from the GST system. GSTR-1 is your detailed report of every outward supply (sale) you made, filed under Section 37 of the CGST Act. GSTR-3B is the summary return where you self-assess your total tax liability, claim Input Tax Credit, and actually pay the tax due under Section 39. Since January 2022, you cannot file GSTR-3B until GSTR-1 for the same period is submitted. This sequential filing rule changed the compliance game for over 1.4 crore registered taxpayers.

What Is GSTR-1? Invoice-Level Sales Return Under Section 37

GSTR-1 is a GST return that captures the complete details of all outward supplies (sales, transfers, exports) made by a registered taxpayer during a tax period. It is filed under Section 37 of the Central Goods and Services Tax (CGST) Act, 2017, and is administered through the GST portal at gst.gov.in. Every registered dealer, manufacturer, and service provider must file GSTR-1 regardless of whether any sales were made.

Think of GSTR-1 as the invoice-by-invoice diary of everything you sold. It does not involve any tax payment. You are simply telling the government: here is who I sold to, what I sold, at what rate, and how much tax I charged. This data is not just for the tax department; it directly feeds into your buyer's GSTR-2B, which determines how much Input Tax Credit they can claim. File GSTR-1 with errors, and your buyer pays the price.

What GSTR-1 Reports

What Is GSTR-3B? Summary Return for Tax Payment Under Section 39

GSTR-3B is a self-assessed summary return where a registered taxpayer consolidates the total output tax liability for a period, claims Input Tax Credit, adjusts ITC against liability, and pays the balance tax through cash or electronic credit ledger. It is filed under Section 39 of the CGST Act, 2017. Unlike GSTR-1, this is the return where actual money moves from your pocket to the government.

GSTR-3B was introduced as a "temporary" simplified return when GST launched on 1st July 2017. The original plan was to replace it with a full return system (GSTR-2 and GSTR-3), but that plan was scrapped. Nine years later, GSTR-3B remains the primary return for tax payment. It is a summary document: you do not report individual invoices here. You report totals: total taxable supplies, total exempt supplies, total ITC available, total ITC reversed, and the net tax you owe.

What GSTR-3B Covers

GSTR-1 vs GSTR-3B: Comprehensive Comparison Table

This table breaks down every meaningful difference between GSTR-1 and GSTR-3B across 16 parameters. If you have ever confused the two or filed the wrong numbers in the wrong return, this comparison will clear things up permanently.

Filing Due Dates: GSTR-1 and GSTR-3B Calendar for 2026

Missing a due date by even a single day triggers late fees. For GSTR-3B, interest also starts accruing at 18% per annum on the unpaid tax amount from the day after the due date. Here is the complete filing calendar for both returns.

Monthly Filers (Turnover Above ₹5 Crore)

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

Sequential Filing Rule: Why You Must File GSTR-1 Before GSTR-3B

If you have tried to file GSTR-3B on the GST portal and found the button greyed out, you already know this rule firsthand. Since 1st January 2022, the GST system enforces sequential filing: GSTR-3B for any tax period cannot be filed until GSTR-1 (or IFF for QRMP taxpayers) for the same period is filed and processed.

This rule was introduced through Rule 59(6) of the CGST Rules, inserted by CBIC Notification No. 1/2022, dated 24th February 2022. The logic is straightforward. Before January 2022, some taxpayers would file GSTR-3B (and pay tax) without filing GSTR-1. This meant the government received tax money, but buyers had no GSTR-2B data, so they could not claim ITC. The mismatch created chaos in the ITC chain.

With sequential filing, the government ensures that your outward supply data is on record before you settle your tax. This protects your buyers, reduces mismatches, and makes reconciliation significantly easier. The trade-off is that if you miss your GSTR-1 deadline, you also miss GSTR-3B by default, stacking penalties for both returns.

Impact of Mismatch Between GSTR-1 and GSTR-3B

Mismatches between GSTR-1 and GSTR-3B are among the top triggers for GST scrutiny notices. The GST system runs automated comparison checks between these two returns, and differences beyond a threshold generate system-level alerts. Here is what happens on both sides of the equation.

When GSTR-1 Shows Higher Liability Than GSTR-3B

If the total tax reported in your GSTR-1 exceeds the tax paid in GSTR-3B, the GST portal generates a Form DRC-01B intimation. This automated notice asks you to either pay the differential tax with interest or explain the discrepancy within 7 days. Ignoring a DRC-01B can escalate to a show-cause notice under Section 73 (non-fraud) or Section 74 (fraud/suppression) of the CGST Act, with penalties ranging from 10% to 100% of the tax due.

When GSTR-1 Shows Lower Sales Than Actual (Under-Reporting)

Under-reporting sales in GSTR-1 while paying correct tax in GSTR-3B creates a different problem. Your buyers will not see those invoices in their GSTR-2B, which means they cannot claim ITC on those purchases. Your buyers may contact you to rectify the GSTR-1, or worse, they may find a supplier who files correctly. Under-reporting also attracts scrutiny during GST audits, where officers compare GSTR-1 with e-way bills, e-invoices, and bank statements.

ITC Reversal Risk for Buyers

Under Rule 36(4) of CGST Rules, a buyer can claim ITC only to the extent it appears in their GSTR-2B (which is generated from suppliers' GSTR-1 data). If your supplier fails to report a sale in GSTR-1 or reports it with incorrect amounts, the ITC on that transaction will not appear in your GSTR-2B. You must either get the supplier to correct their GSTR-1 or reverse the ITC in your GSTR-3B. GSTR-2B is the single source of truth for ITC eligibility.

QRMP Scheme: Quarterly Filing for Small Taxpayers

The Quarterly Return Monthly Payment (QRMP) scheme, introduced from 1st January 2021 through CBIC Notification No. 84/2020, is designed for taxpayers with aggregate turnover up to ₹5 crore. Under QRMP, you file GSTR-1 and GSTR-3B quarterly, but you must still pay tax monthly by the 25th of each month using either the fixed-sum method or the self-assessment method.

How QRMP Works

You opt into QRMP on the GST portal at the beginning of each quarter. Once opted in, you file GSTR-1 once per quarter (by the 13th of the month following the quarter) and GSTR-3B once per quarter (by the 22nd or 24th, depending on your state category). For the two non-filing months within the quarter, you deposit tax via PMT-06 challan by the 25th. The amount can be calculated using the fixed-sum method (equal to the tax paid in the last quarter, divided by three) or the self-assessment method (actual liability for that month).

Invoice Filing Facility (IFF): Helping Your Buyers Claim ITC Monthly

The Invoice Filing Facility (IFF) is an optional tool for QRMP taxpayers. Since you file GSTR-1 only quarterly under QRMP, your B2B buyers would normally wait the entire quarter to see your invoices in their GSTR-2B. IFF solves this. You can upload B2B invoices for the first two months of each quarter (not the third month, which is covered by the quarterly GSTR-1) using IFF on the portal. The upload limit is ₹50 lakh per month. Invoices uploaded through IFF automatically flow into your buyer's GSTR-2B and also auto-populate in your quarterly GSTR-1.

Common Mistakes in GSTR-1 and GSTR-3B Filing

Even experienced accountants slip up on these returns. These are the errors we see most often across the businesses we serve, along with how to avoid them.

GSTR-1 Mistakes

1. Wrong GSTIN of buyer: Entering an incorrect GSTIN means the invoice shows up in the wrong buyer's GSTR-2B. The actual buyer cannot claim ITC. Always verify GSTIN before filing using the GST portal's "Search Taxpayer" feature.
2. Missing B2C large invoices: Inter-state invoices to unregistered persons above ₹2.5 lakh must go in Table 5, not Table 7. Placing them in the wrong table distorts state-wise liability calculations.
3. Not reporting credit/debit notes promptly: Credit notes must be reported in GSTR-1 within the time limit under Section 34 (September of the following year or the date of annual return, whichever is earlier). Delayed reporting means your buyer cannot reduce their ITC.
4. HSN code errors in Table 12: Businesses with turnover above ₹5 crore must report 6-digit HSN codes. Below ₹5 crore, 4-digit codes are required. Wrong HSN codes trigger system-level validation errors.
5. Ignoring IFF under QRMP: Not using IFF means B2B buyers wait a full quarter for their ITC. This is not technically an error, but it damages business relationships.

GSTR-3B Mistakes

1. Claiming excess ITC beyond GSTR-2B: After Rule 36(4) tightening, ITC claims in GSTR-3B Table 4 should not exceed the amount in your GSTR-2B. Excess claims trigger auto-notices.
2. Not reversing ineligible ITC: Blocked credits under Section 17(5), like motor vehicles for personal use, food and beverages, or club memberships, must not appear in ITC. Many businesses claim these and face reversal plus interest during audits.
3. Interest calculation errors: Interest at 18% is calculated on the net tax liability after ITC adjustment, not on the gross tax amount. Overpaying interest is common.
4. Filing nil GSTR-3B when RCM applies: Businesses with no outward supplies but reverse charge liability on services (like legal, GTA) still owe tax. Filing nil GSTR-3B when RCM applies results in short payment.
5. Wrong place of supply for inter-state transactions: Reporting an IGST transaction as CGST+SGST (or vice versa) creates payment mismatches that require adjustment through GSTR-3B of the next period.

How to Reconcile GSTR-1, GSTR-2B, and GSTR-3B

Reconciliation is the process of verifying that the numbers across your GST returns match. If GSTR-1, GSTR-2B, and GSTR-3B tell different stories about the same transactions, you have a problem. Here is a step-by-step approach that works for businesses of any size.

Step 1: Match GSTR-1 Outward Supply Totals With GSTR-3B Table 3.1

Download your GSTR-1 summary and compare the total taxable value and tax amount with what you reported in GSTR-3B Table 3.1. The numbers should match. Common causes of mismatch: invoices entered in GSTR-1 but omitted from GSTR-3B calculation, or adjustments (credit/debit notes) reported in GSTR-1 but not reflected in GSTR-3B. Document every difference with the invoice number and amount.

Step 2: Match GSTR-2B ITC With GSTR-3B Table 4

Your GSTR-2B (generated on the 14th of every month) shows the ITC available based on your suppliers' GSTR-1 filings. Compare the ITC in GSTR-2B with the ITC you claimed in GSTR-3B Table 4. If GSTR-3B ITC exceeds GSTR-2B, you have over-claimed and must reverse the excess. If GSTR-2B shows more ITC than you claimed, you can claim the difference in a subsequent period (subject to the time limit under Section 16(4)).

Step 3: Invoice-Level Reconciliation for B2B Transactions

For B2B transactions, match individual invoices. Download GSTR-1 (your reported sales), GSTR-2B (your suppliers' reported sales to you), and your books of accounts. Use the GST portal's reconciliation utility or any accounting software that supports GST matching. Flag invoices that appear in books but not in GSTR-2B (supplier has not filed) and invoices in GSTR-2B that do not appear in your books (possible duplicate or error from supplier).

Step 4: Rectify Differences in the Next Period's Returns

For GSTR-1 errors, file amendments in the next month's GSTR-1 using Table 9 (for credit/debit notes) or the amendment tables. For GSTR-3B differences, adjust in the next period's GSTR-3B. Maintain a reconciliation register documenting each adjustment for audit trail purposes. The last date for claiming missed ITC or reporting missed invoices is 30th November of the following financial year (for FY 2025-26, the deadline is 30th November 2026).

Penalties for Late or Non-Filing of GSTR-1 and GSTR-3B

The GST law treats late filing and non-filing as compliance defaults, and the penalty structure is designed to hurt. Here is the complete penalty framework for both returns.

E-Invoicing and Its Effect on GSTR-1 and GSTR-3B

E-invoicing has fundamentally changed how GSTR-1 gets populated for larger businesses. If your aggregate turnover exceeds ₹5 crore in any financial year since 2017-18, you must generate e-invoices through the Invoice Registration Portal (IRP) before issuing them to buyers. The e-invoice data automatically flows into GSTR-1 tables for B2B invoices, export invoices, and credit/debit notes. You still need to manually add B2C transactions and any non-e-invoice data.

For GSTR-3B, e-invoicing does not directly auto-populate. However, since GSTR-1 data flows into the auto-populated liability statement of GSTR-3B, the accuracy improvement in GSTR-1 (thanks to e-invoicing) indirectly improves GSTR-3B accuracy. Businesses that adopted e-invoicing report a 30% to 40% reduction in GSTR-1 vs GSTR-3B mismatches because the data entry errors are eliminated at the invoice generation stage itself.

GSTR-1 and GSTR-3B for Specific Business Scenarios

Not every business files these returns the same way. Here is how GSTR-1 and GSTR-3B work in specific situations that cause the most confusion.

Exporters

Exporters report shipments in Table 6 of GSTR-1 with shipping bill number, port code, and invoice details. Exports can be with payment of IGST (claimed as refund later) or under bond/LUT (Letter of Undertaking) without tax payment. In GSTR-3B, export value goes in Table 3.1(b) as "outward taxable supplies (zero-rated)." Exporters can claim refund of IGST paid on exports through Form RFD-01 or RFD-11, which is cross-verified against GSTR-1 Table 6 data.

Businesses With Reverse Charge Obligations

If you receive supplies subject to reverse charge (legal services from advocates, goods from unregistered suppliers under notification, GTA services), the reverse charge liability appears in GSTR-3B Table 3.1(d). GSTR-1 is not involved in reporting inward supplies. The ITC on reverse charge paid can be immediately claimed in the same GSTR-3B period in Table 4, effectively making it a cash-neutral exercise for most transactions.

Multi-State Businesses

Businesses registered in multiple states file separate GSTR-1 and GSTR-3B for each GSTIN. A company with registrations in Maharashtra, Karnataka, and Delhi files 6 returns per month (3 GSTR-1 + 3 GSTR-3B) if filing monthly. Reconciliation becomes complex because inter-branch transfers (stock transfers between states) require proper invoicing with IGST. Each state's GSTR-1 must correctly report supplies to and from other state registrations of the same entity.

Step-by-Step: How to File GSTR-1 on the GST Portal

1. Log in to gst.gov.in: Use your GSTIN, username, and password. Navigate to Services > Returns > Returns Dashboard.
2. Select the return period: Choose the month (monthly filer) or quarter (QRMP) for which you want to file GSTR-1.
3. Add B2B invoices (Table 4): Enter each invoice with buyer GSTIN, invoice number, date, taxable value, rate, and tax. For e-invoice users, this data auto-populates.
4. Add B2C large invoices (Table 5): Enter inter-state invoices to unregistered persons above ₹2.5 lakh with place of supply.
5. Add export data (Table 6): Enter shipping bill details, port code, and invoice values for exports.
6. Add B2C small supplies (Table 7): Enter rate-wise aggregate values for remaining B2C supplies.
7. Add credit/debit notes (Table 9): Report any notes issued against previously filed invoices.
8. Report HSN summary (Table 12): Enter HSN-wise breakup of outward supplies. Mandatory for all taxpayers.
9. Preview and submit: Review the auto-computed summary. Click Submit, then File with DSC or EVC.

Step-by-Step: How to File GSTR-3B on the GST Portal

1. Log in and navigate to Returns Dashboard: Select the period and click "Prepare Online" for GSTR-3B.
2. Review auto-populated data: GSTR-3B now auto-populates liability from GSTR-1 and ITC from GSTR-2B. Review these figures carefully.
3. Table 3.1 (Outward supplies): Verify total outward supply values, including taxable, exempt, nil-rated, and reverse charge supplies.
4. Table 4 (ITC): Confirm the ITC you are claiming matches GSTR-2B. Add any ITC on imports or ISD invoices not auto-populated.
5. Table 5 (Exempt and non-GST supplies): Enter values of exempt, nil-rated, and non-GST inward supplies.
6. Table 6 (Payment of tax): The system calculates IGST, CGST, SGST, and Cess payable. Use ITC from electronic credit ledger first, then pay balance from electronic cash ledger.
7. Create challan and pay: Generate PMT-06 challan for any cash payment due. Pay via net banking, NEFT/RTGS, or over-the-counter.
8. File the return: After payment, submit GSTR-3B using DSC or EVC. Once filed, it cannot be revised.

GSTR-1 vs GSTR-3B: Which Should You Focus On?

This is not an either-or question, but if you asked where to invest more time and attention, the answer is GSTR-1. Here is why: GSTR-3B errors affect you (your tax payment, your ITC claims). GSTR-1 errors affect both you and every buyer you transact with. A single wrong GSTIN entry in GSTR-1 means a buyer somewhere cannot claim their ITC. Multiply that across hundreds of invoices, and you are directly damaging business relationships.

From a practical standpoint, if your GSTR-1 is accurate, GSTR-3B becomes almost automatic. The auto-populated liability in GSTR-3B comes from GSTR-1. The ITC in GSTR-3B comes from GSTR-2B (your suppliers' GSTR-1). So the entire GST system revolves around GSTR-1 accuracy. Invest in getting your invoice data right, and GSTR-3B filing becomes a 15-minute verification and payment exercise.

Key GST Returns Beyond GSTR-1 and GSTR-3B

GSTR-1 and GSTR-3B are the two primary returns for regular taxpayers, but they exist within a broader GST return ecosystem. Understanding how related returns connect to GSTR-1 and GSTR-3B helps you see the full picture.

Related Services for GST-Registered Businesses

GST return filing does not exist in isolation. If you are filing GSTR-1 and GSTR-3B regularly, these related services ensure your broader compliance stays current:

• GST Registration: If you are not yet registered or need state-wise additional registrations for multi-state operations.
• GST Return Filing: Professional monthly or quarterly filing of GSTR-1, GSTR-3B, annual returns, and TDS returns by our in-house GST team.
• Private Limited Company Compliance: Annual ROC filings, board resolutions, and statutory registers alongside GST compliance.
• MSME Registration: Udyam registration for micro, small, and medium enterprises, often required alongside GST registration for government tenders and loan benefits.

Summary

GSTR-1 is the detailed invoice-level return that reports what you sold; GSTR-3B is the summary return where you pay tax and claim ITC. Both are mandatory, filed in sequence (GSTR-1 first), and carry late fees of ₹50 per day plus 18% interest on delayed tax. The sequential filing rule since January 2022 means you cannot skip or delay GSTR-1 without blocking GSTR-3B. For businesses under ₹5 crore turnover, the QRMP scheme offers quarterly filing relief with IFF for B2B invoice reporting. Getting GSTR-1 right is the single most impactful thing you can do for GST compliance, because it feeds GSTR-2B, determines your buyers' ITC, and auto-populates your own GSTR-3B liability. If your GST return filing is overdue or you are receiving mismatch notices, professional assistance can resolve the backlog and set up a system to prevent future issues.