What is GSTR-1?

GSTR-1 is the return of outward supplies where sellers report all sales invoices, debit notes, credit notes, and advances received. The data filed in GSTR-1 is used to populate the recipient's GSTR-2B (their ITC auto-draft).

B2B invoices: Table 4 — invoice-level detail (GSTIN, invoice no., taxable value, GST)
B2C Large (above ₹2.5L inter-state): Table 5 — invoice-level for high-value B2C
B2C Small: Table 7 — consolidated state-wise
Credit/Debit Notes: Table 9 / 10
Advances received: Table 11

Why the 11th Matters for Your Buyers

GSTR-2B for April is generated on 14th May based on all GSTR-1 data submitted by 11th May. If you file GSTR-1 after the 11th:

Your buyers will NOT see these invoices in their May GSTR-2B
They will need to wait until June GSTR-2B — delaying their ITC by one month

Filing GSTR-1 by the 11th is a competitive advantage — your buyers' CFOs will appreciate timely ITC, making you a preferred vendor.

Quarterly Filers (QRMP Scheme)

If your turnover is below ₹5 crore, you may be on the QRMP scheme and file GSTR-1 quarterly (next due: July 2026 for Q1 FY 2025-26). Monthly IFF (Invoice Furnishing Facility) is optional for QRMP filers for B2B invoices.

Action Checklist

[ ] Export all April 2026 sales invoices from accounting system
[ ] Verify GSTIN of all B2B customers (GSTIN search on GST portal)
[ ] Upload B2B invoices, B2C large invoices, CDNs
[ ] Match auto-populated e-invoice/e-waybill data with manual entries
[ ] File GSTR-1 on GST portal by 11th May 2026