How to File GSTR-1: Step by Step (2026)

GSTR-1 reports your outward supplies: every sales invoice, credit note and debit note for the period. It is the first return in the cycle and, since 2025, the one that determines what appears in your GSTR-3B.

That change is why care at this stage matters more than it used to. A GSTR-1 mistake no longer stays in GSTR-1.

When it is due

• Monthly filers: the 11th of the following month.
• QRMP filers: the 13th of the month after the quarter ends.
• IFF (QRMP, months 1 and 2): B2B invoices by the 13th of each month.

The IFF catches people out. Being on the quarterly scheme does not mean nothing is due in months one and two — your B2B invoices still have to be furnished monthly, or your customers cannot claim their credit on time.

Filing it, step by step

1. Log in and open the return. On the GST portal, go to the Returns Dashboard, select the financial year and tax period, and choose GSTR-1.
2. Enter or upload your data. Each transaction type has its own table: B2B, B2C large, B2C small, exports, credit and debit notes, advances, and nil-rated or exempt supplies. Most accounting software exports a JSON in the portal’s format, which is faster and less error-prone than typing.
3. Check the auto-populated e-invoice data. If you generate e-invoices, IRN-linked invoices arrive pre-filled. Verify them against your records before editing anything — a manual edit over correct auto-populated data is a common source of mismatch.
4. Validate before you submit. Check GSTIN formats, invoice numbers and tax computation. The portal will reject malformed GSTINs, but it will happily accept a correctly-formatted GSTIN belonging to the wrong customer.
5. Review the summary. The portal generates a summary of all tables. Cross-check the totals against your sales register. This is the last cheap opportunity to catch an error.
6. Submit and file with DSC or EVC.

The mistakes that cost most

Ranked by how expensive they are to fix rather than how often they happen.

• Wrong customer GSTIN. Your customer does not get their credit, and they will find out and call. Correcting it means an amendment in a later period.
• Missing invoices. Under-reported outward supply flows into GSTR-3B, so you under-pay tax and accrue interest at 18% until it is corrected.
• Editing over correct e-invoice data. Creates a mismatch between the IRN and the return.
• Treating GSTR-1 as a draft. The most expensive habit, and the one the 2025 change made obsolete. See below.

Why a GSTR-1 error is now harder to undo

Before July 2025, an error in GSTR-1 could often be worked around by entering the correct figure in GSTR-3B, because those tables were editable. That is no longer possible: the outward liability in Tables 3.1 and 3.2 of GSTR-3B is auto-populated from GSTR-1 and non-editable on the portal.

Corrections now go through GSTR-1A, and must be made before GSTR-3B is filed for that period. Once GSTR-3B goes in, you are amending in a later period and explaining a mismatch.

In practice this means the reconciliation that used to happen after filing has to happen before it.

GSTR-1 vs GSTR-3B: how the two returns differ

GSTR-1 and GSTR-3B are often described as a pair, and since 2025 they are more tightly linked than ever, but they do not report the same thing and they are not interchangeable. The table below sets out where each stands.

The practical reading is that GSTR-1 is a record and GSTR-3B is a transaction. Get the record wrong and the transaction inherits the mistake, which is the entire reason the 2025 change put more weight on getting GSTR-1 right the first time.

The e-invoicing threshold and what it actually auto-populates

Auto-population of e-invoice data into GSTR-1 only applies to businesses required to generate e-invoices in the first place, and that requirement is turnover-based. E-invoicing became mandatory in stages, starting with the largest taxpayers and extending downward through successive notifications, and the threshold has been lowered several times since it began. Confirm the aggregate turnover figure that currently triggers mandatory e-invoicing on the GST portal or the applicable CBIC notification before assuming a business sits above or below it, because a figure that was accurate a year ago may not be now.

Below the threshold, e-invoicing is optional and invoices have to be entered or uploaded into GSTR-1 the ordinary way, table by table. Above it, IRN-linked invoices arrive pre-filled, which is faster but only safe if it is checked rather than trusted. The auto-populated data reflects what was reported to the Invoice Registration Portal at the time the e-invoice was generated; if a sale was cancelled, amended, or issued with a corrected value afterward outside the IRP process, the GSTR-1 entry will not reflect that automatically.

Worked example: what a missed invoice actually costs

Take a B2B invoice for Rs 2,00,000 taxable value, GST at 18%, Rs 36,000, that gets left out of August’s GSTR-1 entirely. Because GSTR-3B’s outward figure is pulled from GSTR-1, the return for August understates liability by the same Rs 36,000, and that amount goes unpaid for as long as the omission goes unnoticed.

Say the gap is found in October, roughly two months later. Interest under Section 50(1) accrues on the shortfall at the notified rate, currently 18% per annum, for the period it stayed outstanding: Rs 36,000 x 18% x (61/365) works out to a little over Rs 1,000 in interest alone, for an error a same-month reconciliation would have caught for free.

The knock-on cost lands on someone else’s return. The customer’s GSTR-2B for August never showed that invoice, because it was never in your GSTR-1, so the customer’s own August GSTR-3B claimed less input tax credit than it was entitled to. Fixing your GSTR-1 in October does not retroactively fix the customer’s August filing; it shows up in their GSTR-2B for a later period instead. A missed invoice is rarely a problem contained to one business.

The late fee is a waiver, not the full amount

Rs 50 per day, capped at Rs 10,000, is the figure businesses actually pay today, but it is not what Section 47 sets. Section 47 fixes the late fee at Rs 100 per day under each Act, CGST and SGST or UTGST counted separately, subject to a cap tied to turnover in the state or union territory. The lower Rs 50 per day figure in everyday use is a partial waiver of that amount, issued under the government’s power in Section 128, and it applies for as long as the waiver notification stays in force.

That distinction matters because a waiver can be narrowed or withdrawn. If it is, the fee that applies reverts toward the Section 47 figure unless a new waiver replaces the old one. The full late fee breakdown covers the Section 47 figure, the current waiver, and the separate nil-return rate in detail; treat Rs 50 per day as current practice rather than a fixed statutory number.

A short checklist before you file

• Confirm the due date that applies: 11th for monthly filers, 13th after quarter-end for QRMP, and check the IFF deadline separately if the business is on QRMP.
• Check whether the business sits above the current e-invoicing turnover threshold, since that decides whether auto-population applies at all.
• Reconcile the sales register against the return before submitting, not after; this is the cheap correction window described earlier in this guide.
• Verify auto-populated e-invoice data against records rather than assuming it is correct, and resist editing over it unless the underlying record is actually wrong.
• Cross-check GSTIN entries for new or unfamiliar customers specifically, since this is where the wrong-customer error above tends to originate.

Frequently asked questions