What GSTR-1 is
GSTR-1 is the monthly return that every regular GST taxpayer files to declare the supplies they have pushed OUT of their business during a tax period. In plain terms: every invoice you raised, every credit note you issued, every debit note you booked, all of it has to be summarised here and uploaded to the GSTN portal. The return has separate tables for B2B sales (where the buyer is a registered taxpayer and you need their GSTIN) and B2C sales (where the buyer is unregistered or a consumer), plus a separate table for credit and debit notes, advances received, and amendments. Once filed, GSTR-1 feeds straight into your GSTR-3B summary where you actually pay the tax, and it also flows into your customers’ GSTR-2B so they can claim the input tax credit they are entitled to.
Who must file
If you are registered under GST as a regular taxpayer, you file GSTR-1 every month whether or not you did any business in that month — a NIL return is still a return. Composition scheme taxpayers are exempt; they file a single GSTR-4 every quarter instead and never touch GSTR-1. A handful of special categories have their own returns: non-resident taxable persons, OIDAR (online information and database access or retrieval) service providers, and suppliers of online services to unregistered consumers each have separate provisions. The threshold that catches most small traders is the basic vs. composite turnover limit — cross the basic exemption and the moment you register as a regular taxpayer, GSTR-1 becomes your monthly obligation, regardless of whether your turnover is ₹5 lakh or ₹5 crore.
The 11th-of-next-month deadline
The filing date is hard-coded: the 11th of the month following the tax period. So invoices you raised in March are due in GSTR-1 by 11 April. No extensions; no "I’ll do it next week". If you miss it, Section 47 of the CGST Act kicks in with a late fee of ₹50 per day — split as ₹25 CGST and ₹25 SGST — capped at ₹1,000 per return (₹500 each). NIL returns carry a smaller penalty of ₹20 per day (₵10 CGST + ₵10 SGST), capped at ₵500. And interest under Section 50 is a separate beast: 18% per annum on the actual tax that should have been paid but wasn’t, computed day by day. The QRMP scheme is the one legal escape hatch for small taxpayers — you can opt in and pay tax monthly through a challan while filing returns once a quarter — but opting into QRMP does NOT remove your GSTR-1 obligation; the return just shifts from monthly to quarterly.
Common mistakes small traders make
The mistakes that cost traders the most are usually small clerical ones with outsized consequences. First, wrong HSN or SAC codes — the required digit count depends on your aggregate turnover (4 digits below ₹1.5 crore, 6 digits from ₹1.5 to ₹5 crore, 8 digits above ₹5 crore), and a column showing a 4-digit code where a 6-digit one was required can trigger notices. Second, mixing B2B and B2C into a single lump sum without breaking them out — GSTR-1 has distinct tables and reconciling them later is painful. Third, invoice numbers in your books that don’t match what was uploaded; the GSTN cross-checks serial ranges and a missing or duplicated number will halt the next upload. Fourth, forgetting credit and debit notes — they have their own table and are the easiest line item to skip. Fifth, late amendments — you can amend a previous month’s GSTR-1 only up to the November return of the following financial year; after that the figures are frozen. Sixth, GSTR-1 figures drifting away from GSTR-3B — because the 3B self-declaration does not pull live from 1, you can easily end up with mismatched totals that surface as a 2B reconciliation gap during your customer’s ITC claim review.