Filing GSTR-3B accurately every month is essential for maintaining GST compliance and avoiding penalties. Even small data entry errors or mismatches can lead to issues such as incorrect tax liability, ITC disallowance, or unnecessary scrutiny.

This guide explains how to file GSTR-3B correctly, step-by-step, and highlights the most common mistakes businesses make — so you can avoid them and ensure error-free filing.

What is GSTR-3B?

GSTR-3B is a monthly self-declaration summary return that every registered taxpayer must file under the Goods and Services Tax (GST) regime. It contains:

• Outward supplies (sales),

• Inward supplies (purchases),

• Input Tax Credit (ITC) claimed, and

• Tax paid for a given month.

It does not require invoice-level details, but the total values must match your GSTR-1 and GSTR-2B data to avoid discrepancies.

Due Dates and Frequency

• Monthly filing: For most taxpayers, GSTR-3B must be filed by the 20th of the following month.

• Quarterly filing (QRMP Scheme): Taxpayers with turnover up to ₹5 crore can file quarterly GSTR-3B but must pay tax monthly via PMT-06 challan.

Missing the due date attracts late fees and interest on unpaid tax, so timely filing is crucial.

Step-by-Step Guide: How to File GSTR-3B Correctly

Step 1: Log in to the GST Portal

Visit www.gst.gov.in and log in using your GSTIN, username, and password.

Navigate to ‘Returns Dashboard’ → ‘Monthly Return GSTR-3B’.

Step 2: Choose the Return Period

Select the month or quarter for which you are filing the return.

Check the due date displayed — filing beyond this date may incur late fees and interest.

Step 3: Fill Out the Relevant Sections

1️⃣ Outward Supplies (Sales)

• Enter details of all taxable outward supplies, zero-rated supplies, and exempt or nil-rated supplies.

• Separate data for intra-state (CGST/SGST) and inter-state (IGST) transactions.

• Ensure values match your GSTR-1 for the same period.

2️⃣ Inward Supplies (Purchases)

• Enter details of inward supplies attracting reverse charge.

• Verify these with your GSTR-2B statement before filing.

3️⃣ Input Tax Credit (ITC)

• Claim only eligible ITC based on GSTR-2B and actual invoices.

• Adjust ineligible ITC (blocked credits) under the correct head — do not claim them.

• Common examples of ineligible ITC: motor vehicles (except for specific uses), personal expenses, and certain rent or catering costs.

4️⃣ Tax Payment

• The system auto-calculates your total tax liability.

• Use your Electronic Credit Ledger to utilize ITC, and Electronic Cash Ledger to pay any balance due.

Step 4: Preview and Validate Before Submission

Always preview the return before submission. Verify:

• GSTIN and return period

• Total taxable value

• Tax payable and ITC utilized

• Reverse charge entries

Use the “Check for Errors” option on the portal to identify calculation or format issues.

Step 5: File Using DSC or EVC

• Companies and LLPs must file using Digital Signature Certificate (DSC).

• Others (proprietorships, partnerships, individuals) can file using Electronic Verification Code (EVC) sent via OTP.

After filing, download the acknowledgment (ARN) for record-keeping.

10 Common Mistakes to Avoid While Filing GSTR-3B

1️⃣ Mismatch Between GSTR-1 and GSTR-3B

Always ensure your outward supplies in GSTR-3B match the data filed in GSTR-1. Mismatches can trigger notices and block ITC for your buyers.

2️⃣ Claiming ITC Without Verification

Claim ITC only after cross-checking invoices in GSTR-2B. Do not rely on vendor data manually shared — use the official portal for verification.

3️⃣ Not Reporting Reverse Charge Liabilities

If you are liable under reverse charge (like import of services, GTA, or legal services), report and pay the tax in the same month.

4️⃣ Wrong Tax Head Selection

Filing IGST instead of CGST/SGST (or vice versa) is a common mistake — it leads to payment issues and time-consuming corrections.

5️⃣ Failing to Report Nil-Rated or Exempt Supplies

Even if you have no taxable turnover, report nil-rated, exempt, or non-GST supplies to maintain transparency and accurate turnover records.

6️⃣ Ignoring Negative ITC Adjustments

If ITC from earlier months is found to be ineligible later, it must be reversed in the current filing period.

7️⃣ Late Payment of Tax

Pay tax before the due date to avoid 18% interest on unpaid liability.

8️⃣ Not Using Proper Ledgers

Understand how GST ledgers work — use the credit ledger for ITC adjustment and the cash ledger for fresh payments.

9️⃣ Filing Under Wrong GSTIN

Multi-location businesses often mix up state-wise GSTINs; verify before submission.

🔟 Submitting Without Preview

Filing without reviewing summary totals can result in irreversible errors. Once filed, GSTR-3B cannot be revised.

Post-Filing: Best Practices

✔️ Reconcile Regularly

• Reconcile GSTR-1, GSTR-3B, and GSTR-2B monthly.

• Identify missing invoices or mismatches early to avoid notices.

✔️ Maintain Digital Records

Keep a copy of your GSTR-3B acknowledgment and payment challan for audit and future reference.

✔️ File Nil Returns on Time

If no sales or purchases occurred during the period, file a Nil GSTR-3B — non-filing attracts the same late fees as regular returns.

Penalties for Errors or Delays

• Late Fee: ₹50 per day (₹25 each under CGST & SGST), capped at ₹5,000.

• Nil Return Late Fee: ₹20 per day (₹10 each under CGST & SGST).

• Interest: 18% per annum on unpaid tax.

Filing GSTR-3B correctly isn’t just about compliance — it’s about maintaining seamless cash flow, accurate ITC, and avoiding future disputes with the tax department.

Double-check your data, cross-verify with GSTR-1 and GSTR-2B, and use the GST portal’s validation tools before submission.
By following these steps and avoiding the common mistakes, you can ensure error-free, compliant GSTR-3B filings every month.

Also read:
How to Register for GST Online – Your Step-by-Step Guide
Decoding GST Slabs: 5%, 12%, 18%, 28% — Which Applies to You?
Check GSTIN Status & Verify Any Business in India (2025 Guide)
How to File GSTR-3B Correctly (Avoid Common Mistakes)
Penalties for Late GST Filing & How to Avoid Them
Common GST Filing Mistakes Small Businesses Make (and How to Fix Them)