GST Return Filing: Complete GSTR-1 and GSTR-3B Guide 2026

The Goods and Services Tax (GST) return filing system in India is one of the most comprehensive indirect tax compliance frameworks in the world. Every registered taxpayer must periodically report their sales, purchases, tax collected, and tax paid to the government through a set of prescribed returns on the GST portal. While the system has been simplified considerably since its 2017 launch, the number of returns, their interdependencies, and the strict deadlines continue to challenge businesses of all sizes.

This guide walks you through everything you need to know about GST return filing in 2026 — from understanding the different return types to filing GSTR-1 and GSTR-3B step by step, managing Input Tax Credit (ITC) claims, navigating the QRMP scheme, and avoiding the penalties and mistakes that catch thousands of taxpayers off guard every month. Whether you are a small business owner filing your own returns or an accountant managing dozens of GSTINs, this guide will serve as your go-to reference.

Understanding the GST Return Filing System

The GST framework replaced over a dozen central and state taxes with a single unified system. At its core, the return filing mechanism is designed to create a self-policing ecosystem: your outward supply data (what you sold) flows to your buyers as their inward supply data (what they purchased), and any mismatch is flagged automatically. This is why accurate and timely filing is not just a compliance requirement — it directly impacts your trading partners' ability to claim ITC.

Every regular taxpayer interacts primarily with two returns: GSTR-1 (outward supplies) and GSTR-3B (summary return with tax payment). Beyond these, there are annual returns, reconciliation statements, and specialized returns for specific categories of taxpayers. If you need a refresher on when each return is due, see our complete GST filing dates calendar.

Types of GST Returns

The GST Act prescribes several return forms, each serving a distinct purpose. The table below summarizes the most important ones that regular taxpayers need to know about.

For businesses operating under the composition scheme, the filing requirements are different and considerably simpler — they file CMP-08 quarterly and GSTR-4 annually instead of GSTR-1 and GSTR-3B. This guide focuses on the regular taxpayer returns: GSTR-1 and GSTR-3B.

GSTR-1: Filing Your Outward Supplies

GSTR-1 is where you report all the sales and outward supplies you made during the tax period. It is an invoice-level return, meaning you report each invoice individually for B2B (business-to-business) supplies and in aggregate for B2C (business-to-consumer) supplies below the threshold. The data you enter in GSTR-1 flows directly into your buyers' GSTR-2B, allowing them to verify and claim ITC on their purchases from you.

What Data Goes Into GSTR-1

GSTR-1 is divided into several tables, each capturing a specific type of outward supply:

• Table 4 — B2B Invoices: All invoices issued to registered recipients (buyers with a GSTIN). Each invoice is reported individually with the recipient's GSTIN, invoice number, date, taxable value, and tax amounts (CGST, SGST/UTGST, IGST, and cess). This is the most critical section because it directly impacts your buyers' ITC eligibility.
• Table 5 — B2C (Large) Invoices: Invoices to unregistered persons (consumers) where the invoice value exceeds Rs 2.5 lakh. These are inter-state supplies and must be reported with the Place of Supply.
• Table 7 — B2C (Others): Aggregate value of all other B2C supplies (intra-state supplies and inter-state supplies up to Rs 2.5 lakh), reported rate-wise for each state.
• Table 6 — Exports and SEZ Supplies: All export invoices and supplies to Special Economic Zones, with shipping bill details where applicable.
• Table 9 — Credit and Debit Notes: All credit notes (for returns, discounts, or corrections) and debit notes (for additional charges) issued during the period against invoices from the current or previous periods.
• Table 10 & 11 — Amendments: Corrections to B2B and B2C invoices reported in previous periods. This is how you fix errors in earlier GSTR-1 filings since the return cannot be revised.
• Table 12 — HSN Summary: A summary of outward supplies by HSN code. This is mandatory for taxpayers with turnover exceeding Rs 5 crore (at 6-digit HSN level) and for turnover between Rs 1.5 crore and Rs 5 crore (at 4-digit HSN level). Understanding HSN codes and GST rates is essential for accurate reporting.
• Table 13 — Documents Issued: A summary of all documents (invoices, credit notes, debit notes, delivery challans) issued during the period, with serial number ranges.

Step-by-Step GSTR-1 Filing Process

1. Log in to the GST portal (gst.gov.in) using your credentials and navigate to Returns > Returns Dashboard.
2. Select the return period (month or quarter, depending on your filing frequency) and click "Prepare Online" for GSTR-1. You can also prepare the return offline using the GST Offline Tool and upload it.
3. Enter B2B invoice details in Table 4. For each invoice, enter the receiver's GSTIN (you can verify it using our GSTIN verification tool), invoice number, date, total value, taxable value, and tax rate. The portal auto-calculates CGST and SGST/IGST based on the Place of Supply.
4. Enter B2C large invoices in Table 5 and aggregate B2C data in Table 7 with rate-wise breakup for each state.
5. Report credit and debit notes in Table 9 against the original invoice references.
6. Add any amendments to previous period invoices in Tables 10 and 11.
7. Fill the HSN summary in Table 12 with the appropriate level of HSN codes based on your turnover.
8. Complete the documents issued summary in Table 13 with serial number ranges.
9. Preview the return carefully and verify all totals against your books of accounts.
10. Submit and file with DSC (Digital Signature Certificate) or EVC (Electronic Verification Code). Once filed, GSTR-1 cannot be revised.

GSTR-1 Due Dates

• Monthly filers: 11th of the following month (e.g., September 2026 GSTR-1 is due by October 11, 2026)
• Quarterly filers (QRMP scheme): 13th of the month following the quarter (e.g., July-September 2026 quarter is due by October 13, 2026)

GSTR-3B: Summary Return and Tax Payment

GSTR-3B is the monthly or quarterly self-assessment return where you declare your total outward and inward supplies, claim Input Tax Credit, and pay the net tax due. Unlike GSTR-1 which is invoice-level, GSTR-3B deals with aggregate figures. It was introduced as an interim simplified return in 2017 and has since become a permanent fixture of the GST return filing system.

Important: You must file GSTR-1 before you can file GSTR-3B for the same period. The portal enforces this dependency.

What Goes Into GSTR-3B

• Table 3.1 — Outward Supplies: Total taxable value and tax on all outward supplies, divided into taxable, zero-rated, nil-rated, and exempt categories. These figures should reconcile with your GSTR-1.
• Table 3.2 — Inter-state Supplies to Unregistered Persons: State-wise breakup of supplies to unregistered persons and composition dealers.
• Table 4 — Input Tax Credit (ITC): This is the most critical section. It includes ITC available (from imports, domestic purchases, and ISD), ITC reversed (as per Rules 42 and 43, or for other reasons), net ITC available, and ineligible ITC. Your ITC claims must be reconciled with GSTR-2B, the auto-drafted statement generated from your suppliers' GSTR-1 filings.
• Table 5 — Exempt, Nil-Rated, and Non-GST Supplies: Values of supplies that do not attract GST, broken into inter-state and intra-state.
• Table 6.1 — Tax Payable and Paid: The final computation showing total tax liability, ITC utilized, and the balance payable in cash through the Electronic Cash Ledger.

Step-by-Step GSTR-3B Filing Process

1. Ensure GSTR-1 is filed for the same period. The portal will not allow GSTR-3B filing otherwise.
2. Log in and navigate to Returns > Returns Dashboard, select the period, and click "Prepare Online" for GSTR-3B.
3. Review auto-populated values. The portal now auto-populates GSTR-3B with data from your GSTR-1 (liability side) and GSTR-2B (ITC side). Verify these figures against your records.
4. Reconcile ITC with GSTR-2B. Cross-check the ITC suggested by GSTR-2B with your purchase register. Only claim ITC that you are eligible for — matching invoices, received goods/services, and tax paid by the supplier. Do not blindly accept or exceed the GSTR-2B figures.
5. Make any required ITC reversals in Table 4(B) for blocked credits, proportionate reversals for exempt supplies, or ITC on capital goods used partly for personal purposes.
6. Enter exempt and nil-rated supplies in Table 5.
7. Review the tax computation in Table 6.1. The system calculates the net liability after offsetting ITC. Pay the balance through the Electronic Cash Ledger by creating a challan.
8. Offset tax liability following the mandatory order: IGST credit must be used first against IGST liability, then against CGST, then SGST. CGST credit can only offset CGST and IGST. SGST credit can only offset SGST and IGST.
9. Generate the payment challan and deposit the required amount via net banking, NEFT/RTGS, or over-the-counter at authorized banks.
10. Submit and file the return with DSC or EVC after the payment is credited to your Electronic Cash Ledger.

GSTR-3B Due Dates

Penalties and Late Fees for Non-Filing

The GST law imposes strict penalties for late filing or non-filing of returns. Understanding the penalty structure helps you prioritize compliance and avoid unnecessary costs that can add up significantly over multiple periods.

Interest at 18% per annum is calculated on the net tax liability — that is, the total tax payable minus the ITC available. The interest runs from the day after the due date until the actual date of payment. For example, if your GSTR-3B for September 2026 (due October 20) has a net tax payable of Rs 1,00,000 and you file it on November 20, the interest would be approximately Rs 1,479 for the 30-day delay (Rs 1,00,000 x 18% x 30/365).

Common Mistakes to Avoid

Thousands of taxpayers receive notices and face penalties every year due to avoidable errors in their GST returns. Here are the most common mistakes you should guard against:

1. Mismatched Invoice Data Between GSTR-1 and Books

When the invoice details in your GSTR-1 do not match your accounting records — wrong amounts, incorrect GSTINs, transposed invoice numbers — it creates reconciliation issues during annual filing and can trigger scrutiny notices. Always generate GSTR-1 data directly from your accounting software rather than entering it manually on the portal.

2. Incorrect HSN Codes

Applying the wrong HSN code can result in incorrect tax rates, leading to either underpayment (which attracts interest and penalty) or overpayment (which requires a refund claim). Use a reliable HSN code lookup tool to verify codes before filing. Remember that HSN reporting at the 6-digit level is mandatory for businesses with turnover above Rs 5 crore.

3. Overclaiming Input Tax Credit

Claiming ITC in excess of what appears in your GSTR-2B is one of the fastest ways to attract a demand notice. Since the introduction of rule 36(4), you cannot claim ITC beyond the amount auto-populated in GSTR-2B. Always reconcile your purchase register with GSTR-2B before filing GSTR-3B, and follow up with non-compliant suppliers whose invoices are not appearing.

4. Ignoring GSTR-2B Reconciliation

GSTR-2B is auto-generated on the 14th of each month based on the GSTR-1, GSTR-5, and GSTR-6 filed by your suppliers. Failing to review it regularly means you may miss discrepancies until it is too late to rectify them. Set a monthly process to download and reconcile GSTR-2B with your purchase register before the GSTR-3B due date.

5. Missing Amendments for Previous Periods

Since GSTR-1 cannot be revised, the only way to correct errors in a previously filed return is through the amendment tables (Tables 9, 10, and 11) in subsequent months. Many taxpayers forget to report amendments, leaving permanent mismatches in their data. The deadline for amendments is November 30 of the following financial year or the date of filing the annual return, whichever is earlier.

6. Not Filing Nil Returns

Many taxpayers assume that if they had no transactions in a period, they do not need to file returns. This is incorrect. Nil returns are mandatory, and failing to file them attracts late fees of Rs 20 per day. The GST portal offers a quick nil filing option via SMS that takes less than a minute.

QRMP Scheme and Invoice Furnishing Facility (IFF)

The Quarterly Return Monthly Payment (QRMP) scheme is available to taxpayers with an aggregate turnover of up to Rs 5 crore in the preceding financial year. Under this scheme, you file GSTR-1 and GSTR-3B quarterly instead of monthly, significantly reducing the compliance burden. However, tax payment remains a monthly obligation.

How Monthly Tax Payment Works Under QRMP

In the first two months of each quarter, you must pay tax using one of two methods:

• Fixed Sum Method (FSM): Pay an amount equal to the tax paid in the last quarter, divided equally across the three months. This is simpler but may lead to over- or under-payment.
• Self-Assessment Method (SAM): Calculate the actual tax liability for the month based on your transactions and pay accordingly. This is more accurate and recommended for businesses with variable turnover.

The payment must be made by the 25th of the following month using Form GST PMT-06. Any shortfall is adjusted when you file the quarterly GSTR-3B.

Invoice Furnishing Facility (IFF)

One significant drawback of quarterly filing is that your B2B buyers cannot see your invoices in their GSTR-2B until you file your quarterly GSTR-1 — potentially a three-month wait. The Invoice Furnishing Facility (IFF) addresses this by allowing quarterly filers to upload their B2B invoices in the first two months of each quarter.

Key points about IFF:

• It is optional — you are not required to use it
• Only B2B invoices, credit notes, and debit notes can be uploaded (not B2C data)
• The total invoice value uploaded through IFF in any month cannot exceed Rs 50 lakh
• The deadline for IFF is the 13th of the following month (same as quarterly GSTR-1)
• Invoices uploaded via IFF are auto-populated into the quarterly GSTR-1 — you do not need to enter them again
• If you do not use IFF, all your B2B invoices for the quarter will appear in your buyers' GSTR-2B only after you file the quarterly GSTR-1

Using IFF is highly recommended if your buyers depend on timely ITC claims. It maintains your business relationships and ensures your customers are not disadvantaged by your choice of quarterly filing. To understand whether the QRMP scheme is right for your business, also review the GST registration requirements and thresholds.

Tips for Timely and Accurate Filing

Filing GST returns accurately and on time every period requires discipline, good processes, and the right tools. Here are practical tips that can make a real difference:

1. Maintain real-time books: Do not wait until the end of the month to enter invoices. Record every transaction as it happens so your books are always ready for return preparation.
2. Reconcile monthly: Compare your sales register with GSTR-1 data, and your purchase register with GSTR-2B, every month without fail. Catch discrepancies early when they are easy to resolve.
3. Set calendar reminders: Mark the 11th (GSTR-1), 13th (IFF), and 20th (GSTR-3B) of every month. Use our GST filing dates reference to stay ahead of deadlines.
4. Use the correct HSN codes: Invest time in mapping your products and services to the right HSN/SAC codes at the beginning. A reliable HSN lookup tool saves hours of research.
5. Monitor supplier compliance: Your ITC depends on your suppliers filing their GSTR-1. Periodically check their filing status and follow up with non-compliant vendors before it impacts your tax position.
6. File GSTR-1 first: Always file GSTR-1 well before the GSTR-3B deadline. This gives you time to verify the auto-populated GSTR-3B values and make any corrections.
7. Keep digital copies: Maintain organized digital records of all invoices, credit/debit notes, import documents, and payment proofs. The GST law requires records to be maintained for at least six years from the due date of the annual return.
8. Use automation tools: Leverage GST software and tools that integrate with your accounting system to auto-generate returns. Manual data entry on the GST portal is error-prone and time-consuming.

Frequently Asked Questions