GSTR-3B vs GSTR-1 Mismatch Notices: Why They're Issued, How to Reconcile, and the Penalty Exposure

The GST department has one of the most automated tax audit systems in the world. GSTR-1 and GSTR-3B data are compared electronically for every taxpayer, every month. When the numbers don't match, the system flags it — and you receive a scrutiny notice (ASMT-10). If you've received one, or if you want to understand how to prevent it, this step-by-step guide covers the mechanics, the sources of mismatch, the legal exposure, and the exact reconciliation process.

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Understanding the Two Returns

GSTR-1: Invoice-Level Outward Supply Statement

GSTR-1 is a statement of all outward supplies (sales) you made during the tax period. It is filed at the invoice level for B2B supplies and at a consolidated level for B2C supplies.

• For monthly filers: due by the 11th of the following month
• For quarterly QRMP filers: due by the 13th of the month after the quarter

GSTR-1 is a disclosure return — it does not involve any tax payment. When you file GSTR-1, the invoice data flows into your buyers' GSTR-2B, allowing them to see and claim ITC on your supplies.

GSTR-3B: Summary Return with Tax Payment

GSTR-3B is a summary return that covers:

• Total outward taxable supplies (aggregate, not invoice-level)


• Total ITC available and claimed


• Net tax liability


• Actual tax payment (CGST, SGST, IGST)

GSTR-3B is where tax is actually paid. It is filed by the 20th of the following month (for most taxpayers) or the 22nd/24th for QRMP taxpayers.

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What a Mismatch Looks Like

The system compares specific fields between GSTR-1 and GSTR-3B:

Example mismatch: In June 2025, your GSTR-1 shows taxable supplies of ₹30 lakh. Your GSTR-3B for June 2025 shows taxable supplies of ₹26 lakh. The ₹4 lakh gap triggers an automated flag.

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Why Mismatches Occur: Five Common Reasons

Reason 1: Advance Receipts Reported in GSTR-3B but Not in GSTR-1

When you receive an advance for a supply of goods, GST is payable on the advance at the time of receipt (Section 12(2) of CGST Act). Many businesses report this in GSTR-3B (paying tax on the advance) but forget to report the advance in GSTR-1 (Table 11 — Advances and adjustment of advances).

Reason 2: Credit Notes After GSTR-1 Filed Without Adjusting 3B

You issue a credit note in April. You amend GSTR-1 (Table 9B credit notes) in the April return. But you forget to reduce the taxable value in GSTR-3B for April. Now GSTR-1 shows lower taxable value than GSTR-3B — still a mismatch.

Reason 3: Exempt and Nil-Rated Supplies Included Incorrectly

Exempt supplies are reported in GSTR-1 (Table 8) but carry zero tax. In GSTR-3B, they appear in Table 3.1(d) as "exempt supply" with zero tax. The mismatch happens when the taxpayer includes them in the taxable supply columns of either return by mistake.

Reason 4: Inter-State vs Intra-State Classification Error

You sold goods to a customer in another state but treated it as intra-state in GSTR-3B (paying CGST + SGST instead of IGST). When you correctly declared it as inter-state in GSTR-1 (IGST column), the tax component creates a mismatch by component even if total tax is the same.

Reason 5: Clerical Errors and Rounding

Mistyping ₹10 lakh as ₹1 lakh in GSTR-3B, or vice versa. Using invoice-level data with rounding that accumulates into a difference. Entering net-of-discount value in one return and gross in the other.

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The Notice Sequence and Legal Exposure

ASMT-10: Scrutiny Notice

The department issues ASMT-10 under Section 61 of the CGST Act. You have 30 days to respond.

How to respond: File ASMT-11 — a reply to the scrutiny notice — via the GST portal. Your reply must:

• Accept the discrepancy and pay the differential tax (using DRC-03, voluntary payment challan) if it's a genuine error


• Explain why there is no discrepancy with supporting evidence

If Not Resolved: DRC-01 (Show Cause Notice / Demand)

If your ASMT-11 reply is unsatisfactory, the department issues a DRC-01 — a show cause notice under Section 73 or 74.

Section 73 (non-fraud cases):

• Tax + interest under Section 50 (18% per annum from due date)


• Penalty: 10% of tax (minimum ₹10,000) — but if you pay the full demand before the notice or within 30 days of DRC-01, the penalty is waived entirely

Section 74 (fraud / wilful misstatement / suppression of facts):

• Tax + interest


• Mandatory penalty: 100% of tax. Cannot be waived.

Interest under Section 50: 18% per annum on unpaid tax from the due date of filing 3B to the date of actual payment. On ₹10 lakh of differential tax for 12 months, that's ₹1.8 lakh in interest alone.

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Step-by-Step Reconciliation Process

Step 1: Download Your GSTR-1 Data

From the GST portal (gst.gov.in → Returns → GSTR-1 → View Filed Returns), download the filed GSTR-1 for the period(s) under scrutiny. Export to Excel.

Step 2: Download Your GSTR-3B Data

Download GSTR-3B for the same period(s). Note the figures in Table 3.1:

• 3.1(a): Outward taxable supplies (other than zero-rated, nil, and exempt)


• 3.1(b): Outward taxable supplies (zero-rated)


• 3.1(c): Other outward supplies (nil, exempt)

Step 3: Column-by-Column Match

Build a reconciliation table comparing GSTR-1 value, GSTR-3B value, difference, and reason for each supply type and tax component.

Step 4: Identify the Source of Each Difference

For each difference, determine:

• Timing difference: An invoice filed in GSTR-1 for Month 1 was accidentally included in GSTR-3B for Month 2. The overall FY numbers match but the monthly comparison shows differences.


• Genuine error: A figure was mis-entered in one of the returns.


• Classification error: Interstate/intrastate mix-up, taxable/exempt mix-up.

Timing differences resolve themselves when you look at the full year (cumulative GSTR-1 vs cumulative GSTR-3B). If the FY total matches but monthly figures don't, that's the explanation for ASMT-11.

Step 5: Correct the Error or File Explanation

If genuine under-reporting in GSTR-3B: Pay the differential tax via Form DRC-03 (voluntary payment) on the GST portal. Interest is still payable but the penalty is lower (and can be waived if paid before or within 30 days of a notice).

If GSTR-1 error: You can amend GSTR-1 in a subsequent return period using Table 9A (amendment of B2B invoices) or Table 9B (credit notes/debit notes). Note: GSTR-1 amendments can only go up to the return for October of the following financial year.

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The GSTR-2B vs GSTR-3B ITC Mismatch: A Separate but Equally Common Notice

Under Rule 36(4) of the CGST Rules, the ITC you can claim in GSTR-3B cannot exceed the ITC shown in your GSTR-2B (which is auto-populated from your suppliers' GSTR-1 filings). If you claimed ₹5L ITC in GSTR-3B but your 2B shows only ₹4L (because a supplier hasn't filed their GSTR-1), the excess ₹1L is not available.

The only remedy: get your supplier to file their GSTR-1. Until they do, you cannot claim ITC on their invoice.

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FAQ

Q: I received ASMT-10 for a FY 2023-24 mismatch. The period is more than 3 years ago. Is the notice time-barred?

Section 73 demands can be issued within 3 years from the due date of the annual return (GSTR-9) for the relevant FY. For FY 2023-24, the GSTR-9 due date was 31 December 2024, so the Section 73 limitation runs until 31 December 2027. An ASMT-10 in 2026 for FY 2023-24 is well within time.

Q: My GSTR-1 shows higher turnover than GSTR-3B because I included export invoices in GSTR-1 but didn't pay tax on them (exported under LUT). Is this a mismatch problem?

Not a liability mismatch, but it will show as a difference. In GSTR-3B, exports under LUT/bond appear in Table 3.1(b) with zero tax. In your ASMT-11, explain that the difference is zero-rated exports under LUT and provide the LUT reference number.

Q: I voluntarily paid the mismatch amount via DRC-03 before receiving ASMT-10. Does the department still issue a notice?

A DRC-03 voluntary payment ideally stops a notice from being issued. If ASMT-10 still arrives after your DRC-03, reference the DRC-03 challan in your ASMT-11 reply. The payment extinguishes the demand and, under Section 73, the penalty is waived.

Q: My accountant filed GSTR-3B but made errors in five months. The total for the year is correct. How do I explain this?

In your ASMT-11, present a month-by-month reconciliation showing that the FY cumulative GSTR-1 and GSTR-3B values are identical. The monthly mismatches are timing differences, not suppression of income. This is a strong defence under Section 73.

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Fix It Before the Notice Arrives

The GSTR-1 vs GSTR-3B reconciliation should be done every quarter — not only when you receive a notice. A self-initiated DRC-03 payment for a discovered gap costs only the tax and interest. A department-initiated demand after ASMT-10 adds a penalty. A Section 74 fraud determination multiplies the penalty by 10.

For assistance with GST reconciliation, ASMT-10 responses, or proactive mismatch resolution, contact us at harunraaj.com/contact.

Harun Raaj & Associates | NRI Tax Specialists

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