If you run a GST-registered business in India, you've probably asked this at least once:

"What's the difference between GSTR-1 and GSTR-3B? And why do I have to file both every month?"

You're not alone. These two returns confuse thousands of small business owners every single filing cycle.

Here's the short answer: GSTR-1 tells the government what you sold. GSTR-3B tells the government what tax you owe — and proves you paid it.

Both are mandatory. Both have different due dates. And a mismatch between the two can trigger a GST notice — or worse, block your ability to file future returns.

This guide breaks it all down in plain language, with real examples, exact due dates, and a free tool to check your GST calculations before you file.

Quick Summary — GSTR-1 vs GSTR-3B at a Glance

What is GSTR-1?

GSTR-1 is your sales register submitted to the government.

Every invoice you issue to a customer — whether it's a GST-registered business (B2B) or an individual consumer (B2C) — must be reported in GSTR-1 with full details: invoice number, date, GSTIN of buyer, taxable value, GST rate, and tax amount.

Think of GSTR-1 as your public declaration of what you sold. Your buyers use this data to claim Input Tax Credit (ITC). If you don't file it on time, your buyers can't claim their ITC — which creates friction with your customers and damages your business relationships.

What goes into GSTR-1?

• B2B invoices (sales to registered businesses)

• B2C invoices (sales to consumers, typically above ₹2.5 lakh for interstate)

• Credit notes and debit notes

• Export invoices and zero-rated supplies

• HSN/SAC-wise summary of supplies

• Amendments to previous invoices

GSTR-1 due date in 2026

• Monthly filers (turnover above ₹5 crore): 11th of the following month

• Quarterly filers under QRMP (turnover up to ₹5 crore): 13th of the month following the quarter

• GSTR-1A (amendments): Can be filed anytime before GSTR-3B for the same period

Important 2026 update: From February 2025 onwards, HSN-wise reporting in Table 12 of GSTR-1 is mandatory via a dropdown. You cannot type HSN codes manually anymore — they must be selected from the GST portal's dropdown. This means your invoicing software must have accurate, updated HSN/SAC codes.

What is GSTR-3B?

GSTR-3B is your tax payment return — where you actually pay GST to the government.

Unlike GSTR-1, you don't report individual invoices here. You report totals: total taxable sales, total ITC claimed, total tax payable, and total tax paid. It's a self-declared summary, which means the government trusts you to get the numbers right.

This is also why a mismatch between GSTR-1 and GSTR-3B is such a serious problem — the government cross-checks both and expects them to align.

What goes into GSTR-3B?

• Total outward taxable supplies (sales)

• Zero-rated and exempt supplies

• ITC available on purchases (from GSTR-2B)

• ITC reversal (if any ineligible ITC was claimed)

• Net GST payable (IGST, CGST, SGST/UTGST)

• Actual tax payment via Electronic Cash Ledger or Credit Ledger

GSTR-3B due date in 2026

• Monthly filers (turnover above ₹5 crore): 20th of the following month

• Quarterly filers — Category 1 states: 22nd of the month following the quarter

• Quarterly filers — Category 2 states: 24th of the month following the quarter

Real 2026 example: For the March 2026 tax period, the government extended the GSTR-3B due date from 20th April to 21st April 2026 via Notification No. 01/2026-Central Tax. Always check the GST portal around the due date for last-minute extensions.

Critical 2026 update: From July 2025 onwards, certain figures in GSTR-3B — specifically Table 3.2 (inter-state supplies to unregistered persons) — are now non-editable and are auto-populated from your GSTR-1. If there's an error in your GSTR-1, you must correct it via GSTR-1A before filing GSTR-3B. You can no longer manually edit these fields.

The Relationship Between GSTR-1 and GSTR-3B — Why Both Must Match

Here's how to think about it:

GSTR-1 is the story. GSTR-3B is the math.

GSTR-1 tells the government exactly which invoices you issued. GSTR-3B tells them the total tax you calculated from those invoices and proves you paid it.

If the story (GSTR-1) and the math (GSTR-3B) don't add up, the GST department notices — and it triggers problems.

A simple example to make this clear

Ramesh runs a hardware shop in Surat. In May 2026, he sells goods worth ₹10,00,000 with 18% GST. His total GST liability is ₹1,80,000.

• In GSTR-1, he reports each invoice individually — 45 invoices, each with item details, buyer GSTIN, and GST charged.

• In GSTR-3B, he reports the total: taxable value ₹10,00,000, GST payable ₹1,80,000.

Both should match. If Ramesh accidentally reports only ₹8,00,000 in GSTR-3B (perhaps he forgot 5 invoices), there's a mismatch of ₹2,00,000 in taxable value and ₹36,000 in tax — and the GST system will flag it.

Use hisabkitab's free GST Calculator to instantly verify your GST figures before filing: https://hisabkitab.co/gst-calculator-online Enter your sale amount and GST rate — get the exact tax breakup in seconds.

The Filing Order — Which One Do You File First?

Always file GSTR-1 first. Then file GSTR-3B.

This sequence matters because:

1. GSTR-1 auto-populates certain figures into GSTR-3B on the GST portal

2. Your buyers' GSTR-2B (which they use to claim ITC) is generated based on your GSTR-1

3. From July 2025, some GSTR-3B fields are auto-populated from GSTR-1 and cannot be overridden

Filing GSTR-3B before GSTR-1 is technically possible, but it creates mismatches that attract DRC-01C system notices — and recovering from those is time-consuming.

What Happens If GSTR-1 and GSTR-3B Don't Match?

This is where small businesses get into serious trouble.

Rule 88C — The Automated Mismatch Notice

The CBIC introduced Rule 88C to the CGST Rules 2017, which allows the GST portal to automatically detect mismatches between GSTR-1 and GSTR-3B and send taxpayers a notice in Form DRC-01B.

When you receive a DRC-01B, you have 7 days to either:

• Pay the differential tax amount, or

• Explain why there's a difference (with a valid reason)

If you do neither within 7 days, your GSTR-1 filing for the next period gets blocked. You cannot file future returns until the mismatch is resolved.

As of 2026: While Rule 88C has been notified, the specific threshold amounts that trigger automated blocking are not yet fully operational. However, businesses are already receiving mismatch notices under Section 73 of the CGST Act through manual departmental scrutiny. Don't wait for the system to catch up — reconcile proactively.

The Bharti Airtel Case — A ₹923 Crore Warning

One of the most important GST mismatch cases in Indian legal history involves Bharti Airtel.

The company discovered they had overpaid GST by ₹923 crore due to estimation errors in their GSTR-3B returns during GST's early implementation period. They approached the Delhi High Court seeking permission to correct those returns retroactively. The High Court initially ruled in their favour.

But in October 2021, the Supreme Court overturned that decision, holding that GSTR-3B, once filed, cannot be revised for past periods. The ₹923 crore remained locked. The court noted that the errors were made during a period when taxpayers had sufficient opportunity to verify their filings.

The lesson for every Indian business: GSTR-3B cannot be revised after filing. Every figure must be correct before you submit. There is no "undo" button.

Common Reasons GSTR-1 and GSTR-3B Mismatch — And How to Avoid Them

Here are the most frequent causes of mismatches, drawn from CA practice and GST portal data:

1. Timing difference in invoice reporting You issue an invoice on 31st May but record it in June's books. It appears in May's GSTR-1 but June's GSTR-3B. The system flags a mismatch in May. Fix: Always reconcile invoices to the correct tax period before filing.

2. Wrong tax table in GSTR-3B You correctly report a zero-rated export in Table 6A of GSTR-1, but accidentally enter it under Table 3.1(a) in GSTR-3B as a regular domestic taxable supply. The system now sees unreported domestic taxable sales. Fix: Match the supply categories in both forms — especially for exports, exempt supplies, and RCM transactions.

3. Credit note / debit note timing You issue an invoice in one month and a credit note in the next. The invoice is in one period's GSTR-1, the adjustment shows up in a later period's GSTR-3B. Fix: Track credit and debit notes carefully by period.

4. Inter-state supplies to unregistered persons omitted in GSTR-3B These are often forgotten in GSTR-3B (Table 3.2) even when correctly reported in GSTR-1. Fix: From November 2025, this field is auto-populated from GSTR-1. Ensure your GSTR-1 is accurate.

5. Wrong tax head (IGST vs CGST+SGST) You charge IGST on an inter-state supply correctly in the invoice, but in GSTR-3B you accidentally split it as CGST and SGST. Both are technically "tax paid" but under wrong heads. Fix: Verify whether each supply is inter-state (IGST) or intra-state (CGST + SGST) before filing.

6. Typographical errors A ₹1,00,000 invoice accidentally entered as ₹10,00,000 in GSTR-3B. A common human error with serious consequences. Fix: Use accounting software that auto-calculates GST totals from your invoice data — eliminating manual entry errors entirely.

This is exactly what hisabkitab automates. Your GSTR-1 and GSTR-3B figures are both pulled from the same invoice data, so they always match — automatically.

GST Penalties for Late Filing — Exact Amounts (2026)

Late fee for GSTR-1

• ₹50 per day (₹25 CGST + ₹25 SGST) for returns with tax liability

• ₹20 per day (₹10 CGST + ₹10 SGST) for nil returns

• Maximum cap: ₹5,000 per return

Late fee for GSTR-3B

• ₹50 per day (₹25 CGST + ₹25 SGST) for returns with tax liability

• ₹20 per day (₹10 CGST + ₹10 SGST) for nil returns

• Maximum cap: ₹5,000 per return

Interest on delayed tax payment (GSTR-3B)

• 18% per annum on tax not paid by the due date

• Interest starts from the day after the due date

• Even a one-day delay triggers interest

Practical example: If your GST payable is ₹50,000 for May 2026 and you pay it on 25th June (5 days late), the interest is: ₹50,000 × 18% ÷ 365 × 5 = ₹123 in interest — just for 5 days.

Verify your GST amount before the due date using the free hisabkitab GST Calculator: https://hisabkitab.co/gst-calc

ulator-online Don't let calculation errors delay your filing.

GSTR-1 vs GSTR-3B — Monthly Filing Calendar for 2026-27

Note: Due dates may be extended via CBIC notifications. Always verify on gst.gov.in before filing.

What is the QRMP Scheme? (For Businesses Under ₹5 Crore)

If your annual aggregate turnover is up to ₹5 crore, you can opt for the QRMP (Quarterly Return Monthly Payment) scheme.

Under QRMP:

• GSTR-1 is filed quarterly (by the 13th of month after the quarter)

• GSTR-3B is filed quarterly (22nd or 24th depending on your state)

• Tax is paid monthly via challan (PMT-06) for the first two months of each quarter

This reduces your return filings from 24 per year (12 GSTR-1 + 12 GSTR-3B) to 8 per year (4 GSTR-1 + 4 GSTR-3B), with monthly tax payments.

If you are unsure whether QRMP is right for your business, speak to your CA.

A Real-World Reconciliation Checklist (Before You File GSTR-3B)

Use this before hitting submit every month:

• [ ] Is GSTR-1 filed and accepted on the GST portal?

• [ ] Do the total taxable supplies in GSTR-1 match the total in GSTR-3B (Table 3.1)?

• [ ] Are all inter-state supplies to unregistered persons correctly populated in Table 3.2 of GSTR-3B?

• [ ] Does ITC claimed in GSTR-3B match what appears in GSTR-2B for this period?

• [ ] Have you verified HSN-wise summary in GSTR-1 matches the supply totals?

• [ ] Are all credit notes and debit notes correctly accounted for in the right period?

• [ ] Is the tax paid under the correct head — IGST for inter-state, CGST+SGST for intra-state?

• [ ] Have you checked for any pending DRC-01B or DRC-01C notices before filing?

How hisabkitab Makes GSTR-1 and GSTR-3B Filing Easier

hisabkitab is built by Chartered Accountants who file hundreds of GST returns every year. Here's what the software does to eliminate the GSTR-1 vs GSTR-3B mismatch problem:

Auto-populates both returns from the same invoice data. You create invoices in hisabkitab. The software automatically calculates GSTR-1 and GSTR-3B figures from those invoices — so the numbers always match, because they come from the same source.

Flags wrong GSTINs before filing. Invalid GSTINs on B2B invoices are caught before you file GSTR-1, preventing downstream problems with buyer ITC.

HSN/SAC auto-suggestion on every invoice. Select from HSN codes directly on the invoice screen — no manual lookup needed, no entry errors.

AI-powered GSTR-2B reconciliation. hisabkitab matches your purchase invoices against GSTR-2B automatically — showing matched, partial, and unmatched entries before you file.

One-click GSTR-1 and GSTR-3B filing. File directly from hisabkitab to the GST portal — no data re-entry, no export-import headaches.

7-day free trial. No credit card required. Start at hisabkitab.co

The Bottom Line

GSTR-1 and GSTR-3B are two sides of the same compliance coin. One tells the story (your invoices). The other settles the math (your tax payment). They must match — and the government's systems are increasingly automated to catch mismatches instantly.

For small business owners, the simplest way to stay out of trouble is to:

1. Use accounting software that generates both returns from the same invoice data

2. File GSTR-1 before GSTR-3B every period

3. Reconcile your GSTR-2B before claiming ITC

4. Never miss a due date — interest at 18% adds up fast

Before you file, verify your GST calculation with the free hisabkitab GST Calculator: hisabkitab.co/gst-calculator-online Enter your invoice amount and GST rate — get CGST, SGST, and IGST breakup instantly.