How to file GSTR-1, step by step (2026)

If the words ‘GSTR-1’ make your stomach drop, here's the calm version: GSTR-1 is simply a return that lists the sales you made in a period. The tax department already knows you raised invoices — GSTR-1 is how you report them. That's it.

What is GSTR-1?

GSTR-1 is your outward-supplies (sales) return under GST. It groups your invoices into B2B (sales to GST-registered businesses), B2C (sales to end customers), credit/debit notes, exports and an HSN summary.

Here's the part most people miss: your buyers' GSTR-2B — the document they use to claim Input Tax Credit — is built from what you file in GSTR-1. So filing accurately and on time isn't just your compliance; it directly affects whether your customers can claim the tax they paid you.

When is GSTR-1 due?

If you file monthly, it's usually due on the 11th of the following month. If you're under the QRMP (Quarterly Return, Monthly Payment) scheme, it's the 13th of the month after the quarter, though you can push invoice data monthly using IFF. Your turnover and scheme decide which applies — when in doubt, confirm on the GST portal or with your CA.

• Turnover over ₹5 crore: monthly filing.
• Turnover up to ₹5 crore: option of QRMP (quarterly).
• Late filing attracts late fees and delays your buyers' ITC.

The hard way vs the easy way

The hard way is exporting invoices to Excel, reformatting them into the government template, and praying nothing breaks. The easy way: if your invoices already live in one place, the return prepares itself.

In MGH Books, every invoice you raise is already captured, so GSTR-1 is generated for you — B2B, B2C, notes and HSN grouped automatically. You review, fix anything flagged, export the JSON and file.

Step by step

• Enter all your sales invoices for the period (you already do this as you bill).
• Open GST → GSTR-1 and select the month or quarter.
• Review the grouped summary and fix any flagged invoice (a missing GSTIN is the usual culprit).
• Export the JSON, upload it on the GST portal, and file with OTP.

Common mistakes to avoid

• Skipped or duplicate invoice numbers — keep the series unbroken.
• Wrong place of supply — it decides CGST+SGST vs IGST.
• Forgetting credit notes for sales returns — they reduce your liability.
• Filing late — it delays your buyers' ITC and attracts late fees.
• Mismatched HSN summary — keep item HSN codes filled so the summary is correct.

How GSTR-1 connects to 3B and 2B

GSTR-1 (your sales) and GSTR-3B (your monthly summary and payment) should tell the same story; a mismatch is the most common trigger for a GST notice. And your purchases should be reconciled against GSTR-2B to claim the right ITC. When all three are built from one set of books, they reconcile by design instead of by late-night cross-checking.

The bottom line

GSTR-1 is only painful when your sales data is scattered. Keep billing in one connected system and the return becomes a five-minute review, not a monthly scramble — and your customers get their ITC on time, which makes you easier to do business with.