GSTR-3B vs GSTR-1: What Every E-commerce Seller Must Know

Every GST-registered seller files both GSTR-1 and GSTR-3B, every single month, for as long as their registration stays active. Yet a genuinely large number of sellers can't explain the difference between the two beyond "they're both due monthly and I file them with my CA." That gap is exactly where reconciliation errors, missed ITC, and GST notices come from.

The One-Line Difference

GSTR-1 is what you sold. GSTR-3B is what you owe and what you're claiming back.

GSTR-1 is an invoice-level disclosure — every sale, listed individually, by GSTIN, invoice number, tax rate, and value. GSTR-3B is a summary self-assessment — one set of totals for outward tax liability, ITC claimed, and net tax paid. Neither replaces the other. Both are mandatory. They must agree with each other.

Side-by-Side Comparison

	GSTR-1	GSTR-3B
What it reports	Invoice-level outward supplies (every sale)	Summary of tax liability, ITC claimed, and tax paid
Level of detail	Invoice-by-invoice	Consolidated totals only
Due date (monthly filers)	11th of the following month	20th of the following month
Due date (QRMP filers)	Quarterly (IFF monthly option for B2B)	22nd/24th of month after quarter, by state group
Editable after filing?	Amendments only in a later period's return	No — once filed, it's final for that period
Feeds into	Buyers' GSTR-2B (their ITC claim)	Your GST liability payment and your own ITC claim
Payment happens here?	No — informational only	Yes — this is where you pay net GST
Common triggers for notices	Wrong HSN codes, missing invoices, B2B in wrong table	ITC claimed exceeding GSTR-2B, outward supply mismatch with GSTR-1

Why the Order Matters

GSTR-1 is due before GSTR-3B for a reason: your GSTR-1 data becomes your buyers' GSTR-2B, which they use to claim their own ITC. If you file GSTR-1 late, your B2B buyers can't claim ITC on time — a fast way to damage a wholesale relationship. Conversely, your own ITC claim in GSTR-3B depends on your suppliers filing their GSTR-1 correctly and on time, since the ITC portal restricts your claim to whatever shows up in your GSTR-2B.

This creates a chain: your GSTR-1 accuracy affects your buyers → your suppliers' GSTR-1 accuracy affects your GSTR-3B → both returns' accuracy affects your annual GSTR-9. An error anywhere in this chain surfaces later, usually as a notice, rarely as something easy to fix retroactively.

The Reconciliation Every Seller Should Run Monthly

Before filing GSTR-3B, check that:

1. Table 3.1 outward supply value in GSTR-3B matches your GSTR-1 total for the same period. A gap here is the single most common source of a GST mismatch notice.
2. ITC claimed in GSTR-3B Table 4A doesn't exceed what's reflected in your GSTR-2B — since January 2026, the portal actively blocks filing if this gap crosses a threshold (see our GSTR-3B filing guide for the exact restriction).
3. TCS entries from your marketplace (Amazon, Flipkart, Meesho) appear consistently in both returns where applicable.

If you find a mismatch, fix it in the current period's GSTR-1 amendment table rather than trying to force GSTR-3B numbers to reconcile artificially — the department's automated matching will catch a forced reconciliation faster than a genuine late correction.

Which Guide to Read Next

If you need the full step-by-step filing walkthrough rather than the comparison, we have dedicated guides for each:

• How to File GSTR-1 for E-commerce Sellers (FY 2026-27) — table-by-table walkthrough, the 2026 HSN enforcement change, B2B vs B2C entry, and IMS updates.
• How to File GSTR-3B: ITC Reconciliation Guide (FY 2026-27) — the reconciliation-first workflow, the January 2026 ITC claim restriction, and the full portal walkthrough.

For claiming Input Tax Credit correctly once your GSTR-2B is reconciled, see our Input Tax Credit guide. For the annual return that both of these feed into, see GSTR-9 and GSTR-9C explained.

A Quick Example

Say you sold ₹6 lakh worth of goods on Flipkart last month, split across ₹4 lakh B2C and ₹2 lakh B2B. Your GSTR-1 lists every one of those invoices individually — the B2C total in Table 7, the B2B invoices with buyer GSTINs in Table 4. Your GSTR-3B, filed nine days later, simply states: outward taxable value ₹6 lakh, output tax ₹1.08 lakh (at 18%), ITC claimed ₹40,000 (matched against your GSTR-2B), net tax paid ₹68,000. If the ₹6 lakh in GSTR-3B doesn't match the sum of your GSTR-1 invoices for the same period, that's the mismatch the department's system flags automatically — regardless of whether your actual tax payment was correct.

For sellers running quarterly QRMP filing, this reconciliation matters even more, since GSTR-1 detail for the first two months of the quarter only shows up via the optional IFF (Invoice Furnishing Facility), not a full GSTR-1 — meaning three separate data points (two IFF submissions plus one quarterly GSTR-1) all have to tie back to one quarterly GSTR-3B.

Where This Fits With TCS and TDS

E-commerce sellers have an extra reconciliation layer: marketplaces deduct TCS under GST (reflected in GSTR-3B via GSTR-8 filed by the platform) and TDS under Section 194O (an income tax matter, reflected in your AIS/Form 26AS, not your GST returns). Keeping GSTR-1 and GSTR-3B aligned doesn't automatically reconcile these — check the TCS refund guide and the TDS credit guide separately, and use the Section 194O TDS Calculator to estimate what should show up in your AIS before you file.

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Useful tools: GST Due Dates Calendar · GST Late Fee Calculator · Section 194O TDS Calculator · File GST Returns with a CA