GSTR-1 vs GSTR-3B: Due Dates, Differences and the Mismatches That Trigger Notices

For businesses registered under GST, two returns play a critical role in maintaining a clean compliance record: GSTR-1 and GSTR-3B. Although both returns relate to your business transactions and are filed regularly, they serve different purposes. Any significant difference between the information reported in these returns can attract scrutiny and may result in a GST notice.

This guide explains the key differences between GSTR-1 and GSTR-3B, their filing deadlines, common mismatches that may trigger notices, and practical ways to maintain accurate GST compliance.

What Is GSTR-1?

GSTR-1 is a return that reports your outward supplies, or the sales made by your business. It provides detailed, invoice-level information about your transactions, including the customer, goods or services supplied, and applicable tax.

A typical GSTR-1 includes:

• B2B invoices reported with the buyer’s GSTIN

• B2C sales reported in applicable large-value or summary formats

• Exports and supplies to SEZs

• Credit notes and debit notes

• Amendments to previously reported invoices

• HSN/SAC-wise summary of supplies

• Advances received and adjusted

GSTR-1 is a reporting return and does not involve direct payment of tax. However, the information submitted has an important impact on your customers because invoice details reported in GSTR-1 flow into their GSTR-2B. Incorrect or delayed reporting can therefore affect their ability to claim input tax credit.

What Is GSTR-3B?

GSTR-3B is a summary GST return through which tax liability is reported and paid. Unlike GSTR-1, it does not contain invoice-level details. Instead, it consolidates the relevant figures for the tax period.

GSTR-3B generally captures:

• Total outward taxable, zero-rated, nil-rated and exempt supplies

• Supplies subject to reverse charge

• Inter-state supplies to specified categories of recipients

• Eligible ITC, along with reversed or ineligible ITC

• Exempt, nil-rated and non-GST inward supplies

• Interest and applicable late fees

• Tax payment through electronic cash and credit ledgers

Simply put, GSTR-1 reports what you sold, while GSTR-3B reports your tax liability, ITC, and tax payment.

GSTR-1 vs GSTR-3B: Key Differences at a Glance

Parameter	GSTR-1	GSTR-3B
Purpose	Detailed reporting of outward supplies	Summary of sales, ITC, and tax payment
Level of detail	Invoice-wise	Consolidated figures
Tax payment	No	Yes
ITC reporting	No	Yes
Impact on others	Feeds information into the buyer’s GSTR-2B	Determines tax payment and ITC utilisation
Frequency	Monthly or quarterly under QRMP	Monthly or quarterly under QRMP
Late fee exposure	Applicable under GST law	Applicable, with interest on delayed tax payment

The key point is simple: GSTR-1 and GSTR-3B should present a consistent picture of your business transactions.

GSTR-1 and GSTR-3B Due Dates

The applicable due date depends on whether you file returns monthly or under the Quarterly Return Monthly Payment (QRMP) scheme.

Monthly Filers

• GSTR-1: 11th of the following month

• GSTR-3B: 20th of the following month

For example, for the September 2026 tax period, GSTR-1 was due on 11 October 2026, while GSTR-3B was due on 20 October 2026.

QRMP Filers

Under the QRMP scheme:

• GSTR-1: 13th of the month following the quarter, with the option of using the Invoice Furnishing Facility (IFF) for the first two months

• GSTR-3B: 22nd or 24th of the month following the quarter, depending on the state

• PMT-06: 25th of the month for the first two months of the quarter

For Karnataka, quarterly GSTR-3B is filed by the 22nd. Therefore, a Bengaluru-based QRMP taxpayer filing for the July–September quarter would generally file GSTR-1 by 13 October and GSTR-3B by 22 October.

A Note on Due Date Extensions

GST authorities may extend filing deadlines for specific tax periods or regions through official notifications. Therefore, businesses should verify the latest due dates on the GST portal or with a qualified tax professional instead of relying solely on standard deadlines.

Late Fees and Interest

Missing GST filing deadlines can result in additional financial costs.

• Late fee: A per-day late fee may apply to delayed returns, with applicable concessions and limits depending on the return and circumstances.

• Interest on delayed tax payment: Interest may apply to unpaid tax from the applicable due date.

• Interest on wrongly availed ITC: Higher interest may apply where ITC is wrongly claimed and utilised.

Even when there is no tax liability, applicable returns must still be filed. Continuous non-filing can create compliance issues and may contribute to cancellation proceedings against a GST registration.

Why GSTR-1 and GSTR-3B Mismatches Can Trigger Notices

The GST compliance system uses automated data comparisons. Information reported in GSTR-1 and GSTR-3B can be compared, along with supplier and recipient data. Significant differences may attract attention from the tax authorities.

Some common mismatches include:

1. Sales Reported Higher in GSTR-1 Than GSTR-3B

This is one of the most important mismatches. For example, if GSTR-1 reports ₹50 lakh of taxable sales while GSTR-3B reports only ₹40 lakh, the difference may be viewed as under-reporting of turnover.

Common reasons include:

• Invoices reported in GSTR-1 but omitted from GSTR-3B

• Credit notes adjusted differently

• Timing differences between reporting periods

• Data-entry or reconciliation errors

2. Tax Liability Difference Between GSTR-1 and GSTR-3B

Even when taxable turnover appears consistent, differences in tax liability can attract scrutiny.

Possible causes include:

• Incorrect GST rate

• Incorrect place-of-supply treatment

• IGST versus CGST/SGST classification errors

• Manual data-entry mistakes

3. ITC Claimed in GSTR-3B Exceeds GSTR-2B

GSTR-2B provides an auto-drafted view of eligible input tax credit based on supplier filings. If the ITC claimed in GSTR-3B exceeds the available credit reflected in GSTR-2B, the difference may require clarification or reversal.

Businesses should regularly reconcile their purchase records and GSTR-2B before claiming ITC.

4. Reverse Charge Mismatches

Reverse-charge transactions need to be reported correctly in the applicable sections of GSTR-3B. Differences between RCM tax liability, payment, and corresponding ITC can result in reconciliation issues.

5. Locked Inter-State Figures

For the November 2025 tax period onward, certain auto-populated inter-state supply details in Table 3.2 of GSTR-3B are locked and cannot be directly edited. These figures are sourced from GSTR-1 or GSTR-1A.

If the underlying figure is incorrect, the correction needs to be addressed through the applicable GSTR-1A process before filing GSTR-3B. This makes accurate GSTR-1 reporting even more important.

6. Delayed or Non-Filing of GSTR-1

Delayed or missed GSTR-1 filing can prevent customers from seeing their invoices in GSTR-2B. This can affect their ITC claims and may result in follow-ups from customers as well as compliance concerns.

7. Unreported Advances and Amendments

Advances, invoice amendments, and credit notes can easily be missed during reconciliation. When such transactions appear in one return but not the other, differences may arise.

Types of GST Notices You May Receive

Understanding the type of notice received can help you determine the appropriate response.

• GSTR-3A: Reminder notice for non-filing of a return.

• ASMT-10: Scrutiny notice issued when discrepancies are identified during return examination.

• DRC-01B: Intimation relating to differences between liability reported in GSTR-1 and tax paid through GSTR-3B.

• DRC-01: Show cause notice proposing tax, interest, and applicable penalty under relevant provisions.

• ITC mismatch notice: May arise where the ITC claimed does not align with available credit or other GST records.

Ignoring a GST notice can make the situation more complicated. Unanswered notices may lead to further proceedings, demand orders, and other enforcement actions.

Time Limits You Cannot Ignore

From 1 July 2025, certain GST returns, including GSTR-1 and GSTR-3B, cannot be filed on the GST portal once three years have passed from their original due date.

Businesses with pending returns should therefore review and clear outstanding filings as soon as possible to avoid losing the ability to file them through the portal.

How to Prevent GSTR-1 and GSTR-3B Mismatches

Preventive compliance is much easier than resolving a notice. Businesses can adopt the following practices:

1. File GSTR-1 Before GSTR-3B

Complete and verify your outward-supply reporting before filing GSTR-3B to maintain consistency between the two returns.

2. Reconcile Sales Every Month

Compare your books, GSTR-1, and GSTR-3B before filing. Any difference should be identified and properly explained.

3. Reconcile ITC With GSTR-2B

Regularly compare purchase records with GSTR-2B and follow up with suppliers when invoices are missing or incorrectly reported.

4. Record Invoices Regularly

Avoid leaving invoice entries until the end of the month. Timely accounting reduces the possibility of omissions and data-entry errors.

5. Process Credit Notes and Amendments Promptly

Ensure credit notes, debit notes, and invoice amendments are accurately reflected in the relevant GST records.

6. Perform an Annual Reconciliation

Before filing the annual return, reconcile your books, GSTR-1, GSTR-3B and GSTR-2B to identify unresolved differences.

7. Maintain a GST Compliance Calendar

Set reminders before each filing deadline so that returns are not left until the last day.

8. Keep Supporting Documents Organised

Maintain invoices, e-way bills, e-invoice records, bank statements and reconciliation statements. These documents can be valuable when responding to a GST query or notice.

What to Do If You Receive a GST Notice

If you receive a GST notice, take the following steps:

1. Read the notice carefully and identify the notice type, tax period, amount involved, and response deadline.

2. Do not ignore it. Review the issue calmly and determine what caused the discrepancy.

3. Reconcile the figures with your books, GST returns, and supporting records.

4. Pay admitted liability where applicable, along with the required interest.

5. Submit your response within the prescribed deadline with a clear explanation and relevant documents.

6. Consult a GST professional if the issue involves significant tax exposure, ITC disputes or a show cause notice.

Key Takeaway

GSTR-1 and GSTR-3B are closely connected parts of your GST compliance process. GSTR-1 communicates your outward-supply details, while GSTR-3B reports your tax liability, ITC, and payment.

Keeping both returns aligned, reconciling your records regularly, and matching ITC with GSTR-2B can significantly reduce the risk of discrepancies, penalties, interest, and unnecessary GST notices.

Need Help With GST Returns and Notices?

At Mambiz Solutions, we support businesses with monthly and quarterly GSTR-1 and GSTR-3B filing, GSTR-2B reconciliation, GST notice responses, and annual return preparation across Karnataka and India.

Avoid the stress of mismatches and missed deadlines. Contact Mambiz Solutions for a GST compliance consultation and let our experts help keep your GST returns accurate and compliant.

👉 https://mambizsolutions.com/