What is GSTR-1?

GSTR-1 is the monthly or quarterly return in which a registered business reports every outward supply it made — effectively its sales register filed with the government.

It is due on the eleventh of the following month for monthly filers, or by the thirteenth after quarter end under the QRMP scheme. Invoice-level detail is required for business-to-business supplies; business-to-consumer sales can be reported in summary unless they exceed ₹2,50,000.

What you file here flows directly into your customers' GSTR-2B.

Why it matters

Filing GSTR-1 late does not just cost you a late fee — it blocks your customers' input tax credit until you do.

The statutory position

Each figure with the provision it comes from, so it can be checked.
What	Position	Source
Due date, monthly filers	11th of the following month	Notification 83/2020-Central Tax
Due date, QRMP filers	13th of the month following the quarter	Notification 84/2020-Central Tax
Invoice-level reporting	Required for all B2B supplies; B2C reported in summary above thresholds	Section 37 read with Rule 59, CGST Rules 2017
Amendment window	Up to 30 November following the financial year	Section 37(3), CGST Act 2017

Not to be confused with

These get used interchangeably, including by tools that should know better. They are different things.

GSTR-3B

GSTR-1 reports what you sold and carries no payment. GSTR-3B is where tax is actually paid after input credit. Filing one does not file the other, and both are due every period.

GSTR-2B

GSTR-2B is generated for you from your suppliers' GSTR-1 filings. Your GSTR-1 feeds your customers' 2B — the credit chain runs one way.

Questions people ask

What happens to my customer if I file GSTR-1 late?

The invoice misses their GSTR-2B for that month, so they cannot claim the credit until the following period. This is why customers chase GSTR-1 filing, and why a reputation for late filing costs registered customers.

Can I correct an invoice after filing?

Yes, through an amendment in a later GSTR-1, up to 30 November following the financial year. After that the error is permanent, and any credit your customer lost stays lost.

What usually goes wrong

Reporting a B2B invoice as B2C, so the customer never sees it in GSTR-2B
Getting the place of supply wrong on an interstate invoice, which puts the tax under the wrong head
Filing GSTR-3B but leaving GSTR-1 unfiled, which blocks every customer's credit
Leaving credit notes out, so the turnover reported is higher than the turnover earned