GSTR-1 is the return in which you report your sales: every invoice to a registered buyer, a summary of sales to consumers, credit and debit notes, exports and an HSN summary. Your buyers' input tax credit comes from what you report here, so a late GSTR-1 is felt by them as much as by you.
01The due dates
| You file | GSTR-1 is due | Example |
|---|---|---|
| Monthly | 11th of the next month | October 2026 return by 11 November 2026 |
| Quarterly under QRMP | 13th of the month after the quarter | July to September 2026 by 13 October 2026 |
| IFF (optional, QRMP only) | 1st to 13th of the next month, for the first two months of a quarter | October 2026 invoices by 13 November 2026 |
These dates are set by the law and the GST portal shows them on your dashboard, as of October 2026. The government sometimes extends a date by notification, usually after a portal outage or a natural disaster, so check the portal before you plan around an extension.
Monthly or quarterly
If your aggregate turnover in the previous financial year was up to ₹5 crore, you can choose the QRMP scheme and file GSTR-1 every quarter. Above ₹5 crore, you file every month. The QRMP guide explains the choice and the payment rules that come with it.
02What goes into GSTR-1
| Section | What you report |
|---|---|
| B2B | Each invoice to a registered buyer, with the buyer's GSTIN |
| B2CL | Inter-state invoices to unregistered buyers above the limit set for this table |
| B2CS | Other sales to consumers, summarised by state and rate |
| Exports | Export invoices, with or without IGST |
| Credit and debit notes | For registered and unregistered buyers |
| Advances | Tax on advances received, and their adjustment |
| HSN summary | Quantity, value and tax by HSN, split between B2B and B2C |
| Documents issued | The serial ranges of invoices and notes issued in the period |
A Rajkot pump spares dealer with 140 invoices in a month, 60 of them to registered mechanics and workshops, reports those 60 one by one under B2B. The other 80 counter sales go in B2CS as totals by rate.
03How GSTR-1 connects to GSTR-3B
The tax on your sales flows from GSTR-1 into Table 3 of your GSTR-3B. From the July 2025 tax period, the GST portal no longer lets you edit these auto-filled sales figures in GSTR-3B. If GSTR-1 is wrong, you correct it through GSTR-1A for the same period before you file GSTR-3B, or in a later GSTR-1.
So the order each month is: GSTR-1 first, check it, correct anything in GSTR-1A if needed, then GSTR-3B.
04What happens if you file late
Your buyers lose credit for the month
A buyer's GSTR-2B is built from the GSTR-1s that suppliers file by the cut-off. An invoice you report late shows up in the buyer's next GSTR-2B, so their credit slips by a month. Buyers notice, and some hold payment until it appears.
Late fee
GSTR-1 attracts a late fee of ₹50 a day (₹25 CGST and ₹25 SGST), or ₹20 a day for a nil return. Since June 2021 the total is capped by turnover:
| Your case | Maximum late fee per return |
|---|---|
| Nil return | ₹500 |
| Turnover up to ₹1.5 crore | ₹2,000 |
| Turnover above ₹1.5 crore and up to ₹5 crore | ₹5,000 |
| Turnover above ₹5 crore | ₹10,000 |
The late fee and interest guide covers how GSTR-3B is charged, which is where interest applies.
Filing gets blocked
Returns are filed in sequence. If an earlier GSTR-1 or GSTR-3B is pending, the portal will not accept the next GSTR-1. Since the Finance Act, 2023, a return also cannot be filed once three years have passed from its due date, and the GST portal now enforces that limit. Old pending returns should be cleared well before that point.
E-way bills can stop
If you have not filed returns for two consecutive tax periods, generating e-way bills can be blocked until you catch up.
05A monthly routine that works
- On the last working day of the month, make sure every invoice, credit note and debit note for the month is entered.
- Between the 1st and the 5th, check the buyer GSTINs on B2B invoices and the HSN summary.
- File by the 10th, a day before the due date, so that any portal delay does not push you past the 11th.
- Share the filing acknowledgement with buyers who ask, especially large buyers who match credit before they pay.
An Ahmedabad CA firm with a few hundred clients usually runs this as a calendar: sales data from clients by the 5th, GSTR-1 filed by the 10th, GSTR-3B by the 18th.
06Common reasons a GSTR-1 goes wrong
- A buyer's GSTIN typed wrongly, so the credit appears in the wrong account.
- A sale reported as B2CS when the buyer was registered.
- Credit notes forgotten until the end of the year.
- HSN summary totals that do not match the invoice totals.
07Amending a GSTR-1
After filing, you can still correct details in two ways. GSTR-1A lets you add or amend records for the same tax period before you file GSTR-3B for that period. A later GSTR-1 lets you amend an earlier invoice, such as a wrong GSTIN or value, in the amendment tables. Amendments for a financial year are allowed until 30 November after the year ends, or the date you file the annual return, whichever is earlier.
This guide is general information as of October 2026 and does not amount to tax advice.
MatruOS builds the GSTR-1 file from your invoices, with the B2B, B2CS and HSN lines ready to check.