GSTR-1 and GSTR-3B are the two core monthly (or quarterly) GST returns every registered business files, and they serve different purposes. GSTR-1 is a detailed, invoice-level report of all outward supplies (sales) made during the period, businesses list every sales invoice, its GSTIN, value, and tax amount. This is what populates the buyer's GSTR-2B and lets them claim ITC. GSTR-3B, filed shortly after, is a summary return: total sales, total purchases, ITC claimed, and the actual tax payment for the period. It doesn't require invoice-level detail, just the totals. Because GSTR-1 data feeds into buyers' ITC claims, and GSTR-3B is where a business actually pays its GST liability, the two returns must be consistent with each other and with the business's actual books. A mismatch between GSTR-1 and GSTR-3B, or between either return and the general ledger, is a common source of GST department scrutiny and one of the first things reconciled during any GST health check. Two newer mechanisms now sit between the two returns: GSTR-1A lets a supplier amend GSTR-1 data before filing GSTR-3B, and the Invoice Management System (IMS) lets the recipient accept, reject, or keep an invoice pending, with deemed acceptance becoming the statutory basis for claiming ITC from 1 October 2025 onward.
Example: A business's GSTR-1 for the month lists ₹5,00,000 in total sales with ₹90,000 GST. Its GSTR-3B for the same month must report matching sales and tax figures, along with the ITC it's claiming and the net tax actually paid after adjusting for that ITC.
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