GSTR-1 Explained: Reporting Your Sales Correctly

GSTR-1 is the return where you report your outward supplies — your sales — to the GST system, invoice by invoice. It is the other half of the monthly pair with GSTR-3B: GSTR-1 reports the detail, GSTR-3B summarises and pays. And it carries a responsibility beyond your own compliance, because what you file in GSTR-1 becomes the input tax credit your customers can claim. File it wrong or late, and you are affecting their books, not just yours.

This guide covers what goes into GSTR-1, the due date, how B2B and B2C sales are reported differently, and the reconciliation discipline that keeps you off the notice list.

What GSTR-1 is and when it is due

GSTR-1 is a detailed statement of all outward supplies made in a tax period. For monthly filers it is due by the 11th of the following month — so June’s GSTR-1 is due by 11 July. Businesses on the QRMP scheme file GSTR-1 quarterly, with an optional Invoice Furnishing Facility (IFF) to upload B2B invoices in the first two months of the quarter so their customers’ credit is not delayed.

The natural monthly rhythm is GSTR-1 by the 11th, then GSTR-3B by the 20th. Filing GSTR-1 first matters because it populates your customers’ GSTR-2B — the statement they rely on to claim their ITC.

B2B vs B2C: reported differently

GSTR-1 separates your sales by customer type. B2B supplies — to other GST-registered businesses — are reported invoice-by-invoice, with the customer’s GSTIN, because each one flows into that customer’s GSTR-2B as claimable credit. Accuracy here is critical: a wrong GSTIN or invoice number means your customer’s credit does not match, and they may be unable to claim it.

B2C supplies — to unregistered consumers — are generally reported in summary form (rate-wise totals), since there is no buyer GSTIN and no ITC to pass on. However, large B2C inter-state invoices above a threshold are reported individually. The return also captures credit and debit notes, exports, nil-rated and exempt supplies, and advances received.

HSN summary and mandatory detail

GSTR-1 includes an HSN-wise summary of your supplies. The number of HSN digits you must report is tied to your turnover — broadly, more digits for higher turnover. The portal has tightened HSN validation over the last two years, so item masters with correct HSN codes matter: a wrong or vague code can create mismatches and invites scrutiny.

Getting the place of supply right also shows up here — the CGST/SGST vs IGST split reported in GSTR-1 must be correct, or the return will not reconcile with GSTR-3B and the buyer’s state code will not match.

A worked month of GSTR-1

Picture a Bengaluru software services firm in June. It has three kinds of sales to report. First, ₹5,00,000 of services to registered business clients across Karnataka and other states — these are B2B, reported invoice-by-invoice with each client’s GSTIN, so the credit flows to those clients’ GSTR-2B. Second, ₹80,000 of small B2C sales to individual customers — reported as rate-wise summary totals, since there is no GSTIN and no ITC to pass on. Third, one large ₹3,50,000 inter-state B2C invoice — above the threshold, so this one is reported individually rather than in the summary.

The firm also issued a ₹20,000 credit note against an April invoice (a client was over-billed). That credit note is reported in GSTR-1 too, reducing the earlier supply. When all of this is filed by 11 July, each B2B client sees their invoices in their own GSTR-2B, ready to claim — and the firm’s output tax total will need to match what it declares in GSTR-3B by the 20th.

IFF: the QRMP invoice facility

Businesses on the QRMP scheme file GSTR-1 quarterly, but that would leave their B2B customers waiting up to three months to see invoices in their GSTR-2B. The Invoice Furnishing Facility (IFF) solves this: it lets a QRMP taxpayer upload B2B invoices in the first two months of a quarter, so customers get their credit without waiting for the quarterly return. Using the IFF is optional but strongly appreciated by B2B customers, because it keeps their ITC flowing on the normal monthly rhythm.

Amendments: fixing past invoices

GSTR-1 allows amendments to invoices reported in earlier periods, through dedicated amendment tables. If you reported a wrong value, GSTIN, or tax amount, you correct it in a later month’s GSTR-1 rather than editing the original filed return. There is a time limit on amendments — broadly aligned with the annual ITC and return deadlines — so corrections cannot be made indefinitely. The practical lesson is to get invoices right the first time, because downstream amendments ripple into your customer’s credit too.

Why GSTR-1 and GSTR-3B must agree

The output tax you report in GSTR-1 (invoice detail) and the output tax you declare and pay in GSTR-3B (summary) must reconcile. A mismatch between the two is one of the most common automated notice triggers. Mismatches usually arise when the two returns are prepared separately — a credit note in one but not the other, or a manual total that does not tie out. Building both from the same invoice data is the reliable way to keep them aligned.

Frequently asked questions

What is the GSTR-1 due date? The 11th of the following month for monthly filers; quarterly for QRMP taxpayers (with the optional IFF in between).

Do I file GSTR-1 in a month with no sales? Yes — a nil GSTR-1 is still required.

Can I revise GSTR-1 after filing? Not directly — you correct errors through the amendment tables in a later period’s GSTR-1, within the time limit.

Why does my customer say they cannot see my invoice? Usually because the GSTR-1 was filed after their GSTR-2B cut-off, or a GSTIN/invoice-number error means it did not match. It will appear once corrected or in the next 2B.

Does e-invoicing change GSTR-1? Yes, positively — e-invoiced B2B records auto-populate the relevant GSTR-1 tables, reducing manual entry and errors.

How Deskloc Flow files GSTR-1

Deskloc Flow builds GSTR-1 straight from the invoices you have raised — B2B invoices with GSTINs, B2C summaries, credit and debit notes, exports and the HSN summary, all populated automatically. Because the place of supply and tax heads were set correctly at the invoice, the CGST/SGST/IGST split is right, and because GSTR-3B is built from the same data, the two returns reconcile by construction. e-Invoiced records auto-populate, so you are not entering anything twice. The result is a return-ready GSTR-1 for you to review and file on the GST portal.