How to Fix “Tax Amount Mismatch” Error in GSTR-1 Before Filing

Filing GSTR-1 sounds straightforward until the GST portal throws a tax amount mismatch error right before submission. For many business owners and accountants, this error is both confusing and stressful, especially when the filing deadline is close. Understanding why this error appears and how to fix it systematically can save you from penalties, notices, and blocked ITC for your buyers.

This guide breaks down the exact causes of the tax amount mismatch error in GSTR-1 and the step-by-step process to resolve it before you hit the Submit button.

What Is the Tax Amount Mismatch Error in GSTR-1?

The tax amount mismatch error occurs when the taxable value or tax amount reported in one section of GSTR-1 does not match what is reported in another section. The GST portal cross-validates data between multiple tables before allowing you to file. If the numbers do not add up, it flags the return and stops you from proceeding.

The value of supplies in Table 12 is validated against values reported in various other tables, including Tables 4A, 4B, and 6B for B2B supplies, and Tables 5A, 6A, and 7A for B2C supplies. A difference between these tables is what triggers the mismatch warning or error on the portal.

Common Causes of the Tax Amount Mismatch Error

Understanding the root cause is the first step to fixing it correctly.

The most frequent cause is a difference between the invoice-level data entered in the B2B or B2C tables and the HSN-wise summary reported in Table 12. A common issue businesses face is a mismatch between the taxable value reported in the B2B or B2C sections and the HSN summary.

Another common trigger is manually modified tax amounts in invoices. The mismatch due to modified value can be resolved by selecting the exception “Mismatch due to tax amount modified in voucher” and then choosing to recompute the tax values, accept the transaction as is, or resolve based on accounting requirements.

Multi-rate invoices also create problems. If an invoice includes a mix of items, such as one item at 5% GST and another at 0% GST, the entire voucher is reported in the B2B table of the GSTR-1 report, which can result in the HSN summary not matching the invoice-level data.

Wrong or missing HSN codes is another major cause. A mismatched tax rate error occurs when the tax rate applied on an invoice does not match the HSN code of the supply.

Rounding differences, decimal place errors beyond two digits, and zero-value invoices also contribute to the mismatch. GSTR-1 does not accept invoices with a value of zero, and a decimal value in your data with more than two digits will also trigger an error.

The Impact of Ignoring This Error

This error is not just a filing inconvenience. Errors in GSTR-1 do not just affect you — they can block your customers’ ITC, trigger tax notices, and invite penalties. The GST system is interconnected, and one mistake can ripple through the supply chain.

If mismatches are detected, the GST Authority may issue a notice under Rule 88C for clarification on the differing amounts or payment of the tax difference if applicable. Unresolved mismatches can also attract interest at 18% per annum on the unpaid GST amount.

How to Fix the Tax Amount Mismatch Error Before Filing?

The correction process depends on whether you have filed the return yet or are still in the draft stage.

Step 1 — Run a Pre-Filing Reconciliation

Before attempting any fix, reconcile your GSTR-1 data with your sales register and accounting software. Before making any amendment, reconcile your GSTR-1 with your sales register and accounting software to confirm where the actual discrepancy lies.

Step 2 — Cross-Check Table 12 (HSN Summary) Against Invoice Tables

Open your GSTR-1 draft on the portal and compare the taxable value and tax amount in Table 12 against what is entered in Tables 4A, 4B, 5A, and 7A. Taxpayers will see alert messages if there is a mismatch between the values reported in Table 12 and other tables of GSTR-1. Despite the warning, taxpayers can still proceed with filing their GSTR-1 returns in warning mode — but it is always better to correct the numbers before filing to avoid future scrutiny.

Step 3 — Recompute Tax Amounts in Your Accounting Software

If you use TallyPrime, go to the GSTR-1 report, identify the exception flagged, and recompute the tax value. Based on your accounting requirements, you can resolve the mismatch, accept the transaction as is, or recompute the tax values by selecting the relevant exception in the GSTR-1 exceptions report.

For AATO above ₹5 crore, ensure you are using 6-digit HSN codes. As part of the Phase 2 enhancement, reporting HSN codes in Table 12 of GSTR-1 is now mandatory, and businesses with an Aggregate Annual Turnover above ₹5 crore must report 6-digit HSN codes.

Step 4 — Correct B2B and B2C HSN Summary Separately

Table 12 is now divided into two distinct tabs — one for B2B supplies and another for B2C supplies. Taxpayers are required to report the HSN summary separately under these tabs. Mixing up B2B and B2C values in the HSN summary is a direct cause of mismatch errors.

Step 5 — File GSTR-1A If You Discover the Error After Filing

GSTR-1A was reintroduced in August 2024 and allows taxpayers to amend sales invoices reported in GSTR-1 within the same tax period. It should be filed before filing GSTR-3B. This is the cleanest way to correct any mismatch if the error is discovered after the GSTR-1 is filed but before GSTR-3B submission.

Step 6 — Amend in the Next Period If the Deadline Has Passed

If GSTR-3B is already filed, the correction must be done in the GSTR-1 of the subsequent month. You can only make amendments up to 30th November of the following financial year or before you file your annual return, whichever comes first. For FY 2024-25, the deadline falls on 30th November 2025.

Quick Reference: Mismatch Cause and Fix

Mismatch Type	Where It Appears	How to Fix
HSN summary vs B2B invoice value	Table 12 vs Table 4A/4B	Update HSN summary to match invoice totals
Tax rate mismatch on invoice	B2B/B2C table	Verify HSN code and applicable GST rate
Manually modified tax in voucher	TallyPrime exceptions report	Recompute tax or accept as is
Decimal place beyond 2 digits	Invoice entry	Set decimal to 2 digits in software settings
Nil or zero-value invoice	Any table	Remove or correct the zero-value entry
B2B HSN summary left blank	Table 12 (B2B tab)	Add HSN with correct rate or enter nil-rated entry

What Changed in Table 12 from 2025?

From the April 2025 tax period, Table 12 of GSTR-1 now includes two distinct tabs — B2B Supplies and B2C Supplies — and manual entry of HSN codes is no longer permitted. Taxpayers must select the appropriate HSN from a predefined dropdown list.

A new “Download HSN Codes List” button allows taxpayers to download an updated list of HSN and SAC codes in Excel format. Using this list to verify codes before entry eliminates a significant number of mismatch errors.

If you are a B2C-only filer, note that Table 12B (B2C HSN summary) is not mandatory and can be left blank or filled with any value. However, if there are no B2B supplies but there is an entry in Table 8, you still need at least one entry in Table 12A. In this case, you can enter any HSN code with all other fields set to zero to proceed.

How to Prevent This Error in Future Filing Cycles?

Fixing the error once is not enough if the underlying process is broken. To minimize errors, have consistent reporting dates for invoices across both GSTR-1 and GSTR-3B, and provide training to your accounting team on the specifics of GST tables and categories including zero-rated supplies, IGST, CGST, SGST, and credit/debit notes.

It is advisable to have any adjustments such as credit notes, refunds, and advance receipts scheduled for reporting purposes well in advance of the filing date to ensure they accurately reflect in both monthly returns.

Do not amend the same invoice multiple times. Amending the same invoice multiple times not only confuses your records but can also flag your account for scrutiny.

FAQs

Q1. Can I file GSTR-1 despite a tax amount mismatch warning?

Yes, the GST portal currently allows filing in warning mode for HSN-related mismatches. However, filing with a known mismatch can invite scrutiny and may block your buyer’s ITC. It is always advisable to correct the mismatch before filing.

Q2. What is GSTR-1A and how does it help with mismatch errors?

GSTR-1A is an optional amendment form reintroduced from August 2024. It allows you to correct errors in GSTR-1 within the same tax period, before GSTR-3B is filed. This is the most efficient way to fix a mismatch after GSTR-1 submission without waiting for the next filing cycle.

Q3. What happens if the tax amount mismatch between GSTR-1 and GSTR-3B is not corrected? The GST department can issue a notice under Rule 88C asking for clarification or payment of the differential tax amount. Interest at 18% per annum applies on any unpaid liability arising from the mismatch.

Q4. My HSN summary total is slightly off due to rounding. Is that a mismatch?

Yes, even small rounding differences can trigger a mismatch error. Set your accounting software to a maximum of 2 decimal places and verify that the HSN summary is regenerated after any change to invoice data.

Q5. I am a B2C-only business. Why is Table 12 (B2B HSN summary) showing a mandatory error?

From May 2025 onwards, the system mandates at least one entry in Table 12A even for B2C-only filers who have an entry in Table 8. GSTN has clarified that you can add any HSN code with all monetary values set to zero to bypass the validation error without affecting your actual return.

Q6. Can I amend GSTR-1 after filing the annual return GSTR-9?

No. Once GSTR-9 is filed, no further amendments to GSTR-1 for that financial year are permitted. Corrections must be made before filing the annual return or by 30th November of the following financial year, whichever comes earlier.

Q7. Does correcting GSTR-1 automatically update GSTR-3B?

Not automatically. If your amendment or correction in GSTR-1 changes your output tax liability, you must manually adjust the figures in GSTR-3B accordingly and maintain records of all corrections for audit purposes.