GSTR-1 vs GSTR-3B: Key Differences, Reconciliation & Due Dates

A complete 10-minute guide to GSTR-1 vs GSTR-3B: key differences, filing due dates, mismatch risks between sales and summary returns, and step-by-step reconciliation best practices.

If your business is registered under the Goods and Services Tax (GST) in India, two monthly filings govern your tax life: GSTR-1 and GSTR-3B.

For many business owners, tax managers, and accountants, keeping track of these two returns—and ensuring their figures match perfectly every month—is a critical operational task. Filing incorrect data in GSTR-1 or claiming un-reconciled Input Tax Credit (ITC) in GSTR-3B can lead to severe tax notices under Section 73 or 74, automatic recovery proceedings under Rule 88C, blocked e-way bills under Rule 138E, and interest penalties.

In this comprehensive 2026 guide, we break down everything you need to know about GSTR-1 vs GSTR-3B: the fundamental differences, line-by-line comparison, filing schedules, common reconciliation mismatches, automated notice mechanisms, and how to streamline your GST workflow so you never miss a deadline.

1. What is GSTR-1?

GSTR-1 is a statement of outward supplies (sales) made by a registered GST taxpayer during a tax period. It is an information return where you detail every tax invoice, debit note, credit note, advance payment received, and tax rate applicable to your sales.

Core Functions of GSTR-1:

Invoice-Level Data Breakdown: Captures B2B sales with buyer GSTIN, invoice numbers, HSN/SAC codes, place of supply, taxable values, and tax rates.
Passes Credit to Buyers: When you upload B2B invoices in GSTR-1, the GST portal automatically populates your buyers' GSTR-2B statement, allowing them to claim Input Tax Credit (ITC).
No Direct Tax Payment: Filing GSTR-1 does not involve paying tax directly at the time of submission; it simply reports the sales you made.

Structure of GSTR-1 Tables:

GSTR-1 is organized into several key tables that categorize your sales transactions:

Table 4A, 4B, 4C, 6B, 6C: B2B Supplies (Sales to registered buyers).
Table 5: B2C Large Supplies (Inter-state sales to unregistered buyers where invoice value > ₹2.5 Lakh).
Table 7: B2C Small Supplies (Net intra-state & inter-state sales to unregistered buyers).
Table 8: Nil Rated, Exempted, and Non-GST Outward Supplies.
Table 9A, 9B, 9C: Amendments to previously filed invoices, debit notes, and credit notes.
Table 11: Advances received and advances adjusted for services.
Table 12: HSN-wise summary of outward supplies (mandatory 4-digit or 6-digit HSN codes depending on turnover).
Table 13: Documents issued summary (number of tax invoices, credit notes, and delivery challans issued).

2. What is GSTR-3B?

GSTR-3B is a monthly summary return and tax payment statement. Unlike GSTR-1, which requires invoice-by-invoice breakdown, GSTR-3B requires aggregated totals of your sales, output tax liabilities, eligible Input Tax Credit (ITC), and net tax payable.

Core Functions of GSTR-3B:

Summary Totals: Total taxable value and tax split by CGST, SGST, IGST, and Cess.
ITC Claim: Claiming eligible Input Tax Credit based on auto-populated GSTR-2B data.
Actual Tax Payment: Paying net tax liability after setting off ITC against output tax liability using cash ledger deposits.

Structure of GSTR-3B Tables:

Table 3.1(a)-(e): Details of Outward Supplies and Inward Supplies liable to Reverse Charge (RCM).
Table 3.1.1: Supplies made through E-Commerce Operators (under Section 9(5)).
Table 3.2: Inter-State supplies made to unregistered persons, composition dealers, and UIN holders.
Table 4: Eligible Input Tax Credit (ITC Available, Reversed, and Ineligible ITC).
Table 5: Values of exempt, nil-rated, and non-GST inward supplies.
Table 6.1: Payment of Tax (Setting off ITC against Output Liability & Paying Cash Balance).

3. Side-by-Side Comparison: GSTR-1 vs. GSTR-3B

To understand how these two returns complement each other, review this comprehensive comparison matrix:

Feature / Aspect	GSTR-1	GSTR-3B
Nature of Return	Outward Sales Statement	Summary Return & Tax Payment
Detail Level	Invoice-level details (B2B, HSN, Credit Notes)	Aggregated totals (Category-wise summary)
Tax Payment	No tax payment required at filing	Net tax liability must be paid to file
Impact on Buyers	Passes Input Tax Credit (ITC) to your buyers	Does not directly affect buyer's ITC
Filing Frequency	Monthly or Quarterly (QRMP Scheme)	Monthly or Quarterly (QRMP Scheme)
Due Dates (Regular)	11th of the following month	20th of the following month
Revision Allowed?	Amendments allowed in subsequent periods	Amendments allowed in subsequent periods
Late Fee Structure	₹50/day (₹20 for Nil return)	₹50/day (₹20 for Nil return) + 18% p.a. interest
Blocking Mechanism	Blocked if previous GSTR-3B not filed	Blocks GSTR-1 if current GSTR-3B not filed

4. Due Dates and Filing Frequency (2026 Schedule)

Taxpayers are divided into two main categories based on aggregate annual turnover (AATO):

1. Monthly Filers (Turnover > ₹5 Crore)

GSTR-1: Due on or before the 11th of the following month.
GSTR-3B: Due on or before the 20th of the following month.

2. QRMP Scheme Filers (Quarterly Return Monthly Payment, Turnover ≤ ₹5 Crore)

Taxpayers under the QRMP scheme file returns quarterly while depositing tax monthly using Form PMT-06:

IFF (Invoice Furnishing Facility): Optional upload of B2B invoices on 13th of Month 1 & Month 2.
Fixed Sum Method vs Self Assessment Method: In Month 1 & Month 2, pay 35% of past tax or self-assessed tax via PMT-06 by the 25th.
Quarterly GSTR-1: Due on the 13th of the month following the quarter.
Quarterly GSTR-3B: Due on the 22nd or 24th of the month following the quarter (depending on State Category A/B).

5. Automated Tax Notices: Rule 88C and Rule 88D

The GST portal runs automated data validation algorithms between GSTR-1, GSTR-2B, and GSTR-3B to catch discrepancies instantly.

Rule 88C: GSTR-1 vs. GSTR-3B Sales Discrepancy (Form DRC-01B)

If the output tax liability reported in your GSTR-1 exceeds the output tax paid in GSTR-3B by a pre-defined threshold percentage or amount, the portal automatically issues a system-generated notice in Form DRC-01B.

Requirement: You must either pay the differential tax along with interest OR submit an acceptable explanation within 7 days.
Consequence of Non-Compliance: If you fail to respond or pay within 7 days, your GSTR-1 for the subsequent month will be automatically blocked, and recovery proceedings under Section 79 may be initiated by the tax department.

Rule 88D: GSTR-2B vs. GSTR-3B ITC Discrepancy (Form DRC-01C)

If the Input Tax Credit claimed in GSTR-3B exceeds the ITC available in GSTR-2B by a specified threshold, an automated notice in Form DRC-01C is generated.

Requirement: You must pay back the excess ITC with 18% annual interest OR submit a reconciliation response explaining the discrepancy within 7 days.
Consequence of Non-Compliance: Non-response leads to blocking of subsequent GSTR-1 filings.

6. Understanding Input Tax Credit Reversals (Rule 37 and Rule 42/43)

In addition to matching GSTR-1 and GSTR-3B, taxpayers must correctly handle ITC reversals in Table 4(B) of GSTR-3B:

1. Rule 37: Non-Payment to Vendor within 180 Days

Under GST law, if you fail to pay your vendor the invoice value + tax within 180 days from the invoice date, you must reverse the ITC previously claimed on that invoice in GSTR-3B, along with 18% annual interest. Once payment is made to the vendor in a future month, the ITC can be reclaimed in Table 4(A)(5).

2. Rule 42 & 43: Common ITC Reversal for Exempt Supplies

If you use inputs or capital goods for making both taxable and exempt supplies (or for personal use), you must reverse the proportionate ITC calculated as per Rule 42 (inputs/input services) and Rule 43 (capital goods).

7. Common Causes of GSTR-1 vs. GSTR-3B Mismatches

Understanding why mismatches occur helps you fix your internal accounting workflows before filing:

Credit Note Adjustments: Issuing a credit note in GSTR-1 but forgetting to adjust output liability in GSTR-3B.
Reverse Charge Mechanism (RCM): Failing to include RCM liability in Table 3.1(d) of GSTR-3B while reporting vendor invoices.
Unadjusted Advances: Tax paid on advances received in GSTR-1 Table 11 not properly adjusted against final invoice issuance in subsequent months.
Data Entry Errors: Rounding differences or manual typing mistakes when entering figures directly on the GST portal without software integration.

8. Step-by-Step Monthly GST Filing & Reconciliation Workflow

To ensure 100% compliance and zero tax notices, follow this monthly 5-step checklist:

  Step 1: Record All Sales & Purchase Invoices in Accounting System
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  Step 2: File GSTR-1 on or before 11th (Upload B2B & B2C Sales)
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  Step 3: Download Auto-Populated GSTR-2B Statement on 14th
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  Step 4: Reconcile Books Purchase Register against GSTR-2B
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  Step 5: File GSTR-3B on 20th (Setoff ITC & Pay Cash Tax Liability)

9. Penalties, Late Fees, and Interest for Late Filing

Missing GST deadlines leads to cumulative financial penalties and operational disruptions:

Late Fees (Per Day):

Regular Taxpayer with Sales: ₹50 per day (₹25 CGST + ₹25 SGST) up to maximum capped limits (₹500 to ₹10,000 based on turnover).
Nil Taxpayer (Zero Sales & Purchases): ₹20 per day (₹10 CGST + ₹10 SGST).

Interest on Unpaid Tax:

If tax liability is paid after the due date, 18% per annum interest is calculated on net cash tax paid late.
If ineligible ITC is wrongly claimed and utilized, 18% per annum interest is levied on the utilized amount.

E-Way Bill Blocking (Rule 138E):

If a taxpayer fails to file GSTR-3B for two consecutive months, their E-Way Bill generation facility is automatically blocked on the E-Way Bill portal, halting all physical goods movement.

10. Automating GST Filing & Reconciliation with ForkOST

Manual GST filing using spreadsheets and manual portal uploads is slow, error-prone, and risky.

ForkOST streamlines your entire GST compliance lifecycle:

Instant GSTR-1 Generation: Automatically compiles B2B, B2C, HSN, and Credit Note summaries directly from your sales vouchers.
Automated GSTR-2B Reconciliation: Matches supplier bills against portal GSTR-2B data, highlighting un-reconciled invoices in one click.
Auto-Calculated GSTR-3B: Pre-populates GSTR-3B tax liabilities and eligible ITC limits, preventing DRC-01B/C mismatch notices.
Audit-Ready Logs: Tracks every amendment, credit note, and tax adjustment with complete ledger traceability.

11. Frequently Asked Questions (FAQ)

Q1: Can I file GSTR-3B without filing GSTR-1?

No. Under current GST rules, the GST portal blocks GSTR-3B filing if the GSTR-1 for the corresponding tax period has not been submitted.

Q2: What should I do if I made a mistake in GSTR-1?

You cannot revise a filed GSTR-1 return directly. However, you can make amendments (Table 9A, 9B, 9C) in the next month's GSTR-1 filing to correct invoice numbers, values, or tax rates.

Q3: What is the difference between GSTR-2A and GSTR-2B?

GSTR-2A: A dynamic, real-time read-only statement that updates whenever a supplier uploads an invoice.
GSTR-2B: A static, monthly auto-drafted ITC statement generated on the 14th of every month. Legal ITC claims in GSTR-3B must strictly be based on GSTR-2B, not GSTR-2A.

Q4: What happens if I claim ITC in GSTR-3B that is not in GSTR-2B?

Claiming ITC not reflected in GSTR-2B triggers an automated Form DRC-01C notice under Rule 88D. You will be required to explain the mismatch or pay back the excess ITC with 18% annual interest.

12. Conclusion

Understanding the distinct roles of GSTR-1 and GSTR-3B is essential for running a compliant, stress-free business in India. By maintaining clean books, filing GSTR-1 on the 11th, and reconciling purchase registers against GSTR-2B before filing GSTR-3B on the 20th, you protect your cash flow and avoid costly penalties.

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GSTR-1 vs GSTR-3B: Key Differences, Reconciliation, and Due Dates (2026)