GSTR-1 vs GSTR-3B: Key Differences, Due Dates & Filing Rules 2026

GSTR-1 vs GSTR-3B: What's the Real Difference, and Why Does It Matter?

If you're registered under GST, you'll file both GSTR-1 and GSTR-3B, usually within days of each other, every single month or quarter. Yet a surprising number of business owners still treat them as two versions of the same thing. They aren't.

In one line: GSTR-1 is an invoice-wise statement of everything you sold, filed only for reporting — it carries no tax payment. GSTR-3B is a summary return where you actually calculate and pay your net GST liability. One tells the government what you sold; the other tells it how much you owe and settles that amount.

Getting this distinction wrong is not a paperwork technicality. In 2026, a mismatch between the two returns can auto-trigger a notice, block your next filing, or freeze your buyer's input tax credit (ITC). This guide breaks down exactly how the two returns differ, when each is due, what happens if they don't match, and how to file both correctly — in sequence, on time, every period.

If you'd rather have a professional handle the actual filing for you instead of tracking every rule yourself, LegalDev's GST return filing service takes care of GSTR-1, GSTR-3B, and GSTR-9 end to end.

What Is GSTR-1?

GSTR-1 is the Statement of Outward Supplies — a return where you report every sale, export, credit note, debit note, and advance received during the tax period, invoice by invoice. It's filed under Section 37 of the CGST Act and forms the backbone of India's invoice-matching system.

Think of GSTR-1 as the "evidence" return. It doesn't calculate what you owe; it simply lays out your sales data so the system can flow that information to your buyers' GSTR-2B (their auto-drafted ITC statement).

What GSTR-1 covers:

• B2B and B2C invoices (with GSTIN-wise detail for B2B)
• Exports and supplies to SEZ units
• Credit notes and debit notes issued
• Advances received against future supplies
• Nil-rated, exempt, and non-GST outward supplies
• HSN-wise summary of goods/services sold

Who files it, and when:

• Monthly filers (turnover above ₹5 crore, or smaller taxpayers who haven't opted into QRMP): due on the 11th of the following month.
• QRMP filers (turnover up to ₹5 crore, opted into Quarterly Return Monthly Payment): file GSTR-1 quarterly by the 13th of the month after the quarter, but can optionally upload B2B invoices monthly via the Invoice Furnishing Facility (IFF) so their buyers get ITC visibility without waiting a full quarter.

Once filed, GSTR-1 cannot be revised for that period. Corrections flow through GSTR-1A (a same-period amendment window before GSTR-3B is filed) or through amendment tables in a later period's GSTR-1, subject to the standard cut-off of 30 November following the end of the financial year.

What Is GSTR-3B?

GSTR-3B is the monthly (or quarterly) self-declared summary return. This is where the actual tax gets paid. It consolidates your outward supplies, inward supplies liable to reverse charge, ITC claimed, and net cash/ITC liability into a single set of totals — no invoice-level detail required.

What GSTR-3B covers:

• Summary of outward and inward supplies
• ITC available (auto-populated from GSTR-2B), claimed, and reversed
• Tax payable and tax paid, split across IGST, CGST, SGST, and cess
• Interest and late fee, where applicable

Who files it, and when:

• Monthly filers: due on the 20th of the following month.
• QRMP filers: due on the 22nd or 24th of the month after the quarter, depending on whether your registered state falls in Category X or Category Y — but note that QRMP taxpayers still pay tax every month using Form PMT-06, even though the return itself is filed quarterly.

A GSTR-3B (Nil or otherwise) must be filed for every period, even with zero transactions. And since 2022, the GST portal auto-populates your outward-supply figures in GSTR-3B directly from GSTR-1/1A/IFF — which is exactly why filing sequence and accuracy in GSTR-1 matters so much (more on this below).

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

GSTR-1 and GSTR-3B Due Dates for FY 2026-27

Note: these are the standard due dates. CBIC does occasionally extend deadlines through formal notifications — for instance, the GSTR-3B due date for March 2026 was pushed from 20 April to 21 April 2026 following a GST portal outage. Always cross-check the GST portal or a current CBIC notification before assuming a date, especially close to a deadline.

Why GSTR-1 Must Be Filed Before GSTR-3B

This isn't just good practice — it's now a structural rule. A few things make the sequence non-negotiable in 2026:

1. Auto-population is hard-linked. Since the 2025 hard-locking update, the tax liability tables in GSTR-3B pull directly from your GSTR-1, GSTR-1A, and IFF data and are no longer manually editable. If GSTR-1 has an error, that error flows straight into GSTR-3B.
2. Sequential filing is enforced. Under Rule 59(6), you cannot file GSTR-1 for the current period if you haven't filed GSTR-3B for the prior one. In effect, the two returns lock each other's filing chain — skip one and the next period's filings stall.
3. Buyer ITC depends on it. Your customer's GSTR-2B — and therefore their ability to claim ITC — is built from your GSTR-1. A late or incorrect GSTR-1 delays credit for every buyer downstream, which is a real relationship cost, not just a compliance one.

Practical filing order every period: File GSTR-1 (or IFF) with correct invoice data → review/amend via GSTR-1A if needed → file GSTR-3B, claiming only the ITC that actually appears in your GSTR-2B → pay any balance tax and file.

Late Fees and Interest: GSTR-1 vs GSTR-3B

A useful rule of thumb: GSTR-1 late fees punish delay in reporting; GSTR-3B late fees plus interest punish delay in paying. Missing GSTR-3B is almost always the costlier mistake because interest compounds daily on top of the flat late fee.

How GSTR-1 and GSTR-3B Reconcile: Rule 88C, Rule 88D, DRC-01B & DRC-01C

Because GSTR-1 reports what you sold and GSTR-3B reports what you paid, the two are supposed to agree. When they don't, the system reacts automatically — no manual scrutiny required anymore.

Rule 88C — outward tax mismatch (Form DRC-01B): If the tax liability shown in your GSTR-1/IFF for a period is higher than what you actually declared and paid in GSTR-3B, beyond a threshold (commonly cited as more than 20% of the difference, or ₹25 lakh, whichever applies), the portal auto-generates an intimation in Form DRC-01B. You get 7 calendar days to either:

• Pay the shortfall through Form DRC-03 along with Section 50 interest, or
• File a written explanation on the portal (genuine reasons include credit notes issued later, amendments, or a timing difference).

Ignore the notice, and the department can treat the gap as unpaid tax and move straight to recovery under Section 73 or 74 — no separate show-cause notice required first.

Rule 88D — excess ITC claimed (Form DRC-01C): This works on the input side. If the ITC you've claimed in GSTR-3B exceeds what's actually available in your auto-drafted GSTR-2B beyond the prescribed threshold, you'll receive a DRC-01C intimation with the same 7-day window to pay back the excess or explain it. Since Section 16(2)(aa) is strictly enforced, provisional ITC claims beyond what GSTR-2B reflects are no longer accepted — you can only claim what your suppliers have actually reported in their own GSTR-1.

Why this matters for buyers, not just sellers: if a key vendor delays their GSTR-1, your GSTR-2B — and your eligible ITC — gets delayed with them. It's worth building GST-compliance checks into how you choose vendors, not just how you file your own returns.

Common GSTR-1 vs GSTR-3B Mismatches — and How to Fix Them

GSTR-1 vs GSTR-3B: Quick Decision Summary

• Need to report your sales for buyer ITC visibility? That's GSTR-1.
• Need to actually pay your GST liability? That's GSTR-3B.
• Filing order: Always GSTR-1 (or IFF) first, GSTR-3B second — the system enforces this and auto-populates accordingly.
• Both mandatory, even with no transactions: file Nil returns for both to avoid late fees and to keep your compliance record clean, since a clean filing history also matters for your GST compliance rating visible to potential business partners.

For a full walkthrough of registration, return types (GSTR-1, 3B, 9, 9C), and expert-assisted filing, see LegalDev's complete GST return filing guide.

Frequently Asked Questions

1. Can I file GSTR-3B without filing GSTR-1 first?

Technically the portal may allow it in some situations, but doing so almost guarantees a mismatch under Rule 88C, since GSTR-3B's liability tables are auto-populated from GSTR-1. It also risks your buyers' ITC visibility. Always file GSTR-1 first.

2. What happens if I file GSTR-1 but skip GSTR-3B for that period?

Under Rule 59(6), you'll be blocked from filing GSTR-1 for the next period until the pending GSTR-3B is filed. Interest also starts accruing on any unpaid tax from the original due date.

3. Is GSTR-1 required if my GSTR-3B shows Nil tax liability?

Yes. GSTR-1 and GSTR-3B are separate, independent obligations. Even a Nil GSTR-3B period still requires a GSTR-1 (Nil, if there were genuinely no outward supplies).

4. How is GSTR-9 different from GSTR-1 and GSTR-3B?

GSTR-9 is the annual return that reconciles all your monthly/quarterly GSTR-1 and GSTR-3B filings for the full financial year. GSTR-1 and GSTR-3B are periodic; GSTR-9 is a once-a-year summary and cross-check of everything already filed.

5. What triggers a DRC-01B or DRC-01C notice, and how urgent is it?

DRC-01B fires when GSTR-1 liability exceeds GSTR-3B tax paid beyond the prescribed threshold; DRC-01C fires when ITC claimed in GSTR-3B exceeds what's available in GSTR-2B. Both give you exactly 7 calendar days to pay the difference via DRC-03 or file an explanation — treat it as urgent, since unresolved notices can escalate to formal demand proceedings.

6. Can GSTR-1 be revised after filing?

No, GSTR-1 cannot be revised once submitted. Same-period corrections go through GSTR-1A before you file GSTR-3B; later corrections go through amendment tables in a subsequent GSTR-1, subject to the 30 November cut-off following the relevant financial year.

In Short

GSTR-1 and GSTR-3B aren't interchangeable, and they aren't optional extras of each other — they're two legally distinct returns that the GST system now checks against each other automatically. File GSTR-1 accurately and on time, let it flow into GSTR-3B, reconcile against GSTR-2B before claiming ITC, and pay by the due date. Get that sequence right every period, and mismatch notices like DRC-01B and DRC-01C simply stop being a recurring problem.

If tracking due dates, reconciling ITC, and responding to portal notices isn't something you want to manage manually, LegalDev's GST experts can handle your GSTR-1, GSTR-3B, and GSTR-9 filing end to end — accurate, on time, every period. You can also explore other GST tools and compliance guides at legaldev.in.

Sources for Verification

• GST Portal — www.gst.gov.in
• CGST Act, 2017 — Sections 37, 39, 47, 50
• CGST Rules — Rules 59(6), 88C, 88D
• CBIC Notifications on late fee caps (Notification Nos. 19/2021 and 20/2021 – Central Tax) and periodic due-date extensions