GSTR-3B Filing Guide: Auto-Populated Liability, ITC Offset, and What to Check Before You File

GSTR-3B's outward liability figures are drawn from your filed GSTR-1 for the period; the ITC side draws from your reconciled GSTR-2B. "Auto-3B" isn't a different return — it's GSTR-3B pre-filled from data you've already reported elsewhere, so the two returns can't silently drift out of agreement. If GSTR-1 for the period isn't filed yet, or GSTR-2B reconciliation isn't complete, the auto-populated GSTR-3B is only as reliable as the inputs feeding it.

Once liability and eligible ITC are established, offset has to follow the prescribed order — IGST credit first against IGST liability, then CGST and SGST — before any cash payment is required through the GSTN ledger. Getting the offset sequence wrong doesn't just complicate the return; it can leave IGST credit stranded when it should have absorbed CGST/SGST liability instead.

The checks that catch most rejections and notices are unglamorous: HSN codes that don't match the GSTN master, place-of-supply values that don't align with the buyer's GSTIN, RCM liability classified incorrectly, and ITC claimed on line items blocked under Section 17(5). Each of these passes an exact-match validation but fails GSTN's own checks — which is why they're worth validating explicitly rather than assuming a clean-looking return is a correct one.

Every liability calculation, offset action, and payment should leave an audit trail — not just the ARN, but the intermediate numbers that produced it. That record is what makes a Section 61/73/74 notice answerable months later, when nobody remembers the reasoning behind a specific offset decision from memory.