How to File GSTR-1 in 2026 - Complete Step-by-Step Guide for Indian Businesses

Every Indian business registered for GST must file a GSTR-1 return - monthly if turnover is above ₹5 crore, quarterly otherwise. Miss the 11th of the month and your buyer can't claim ITC. Get one row wrong and your GSTR-2A reconciles to nothing. This guide walks you through filing GSTR-1 on the gst.gov.in portal end-to-end, with the exact tables you need, and how to skip the manual data-entry pain entirely.

1. What is GSTR-1 (and why it matters)

GSTR-1 is the monthly (or quarterly) return where you report every outward supply - every invoice you raised in the period. The government uses it for two things:

1. To allow your buyer to claim Input Tax Credit (ITC). Until you file GSTR-1, every B2B invoice you raised is invisible in your buyer's GSTR-2A. They can't claim the GST you charged them. This becomes a relationship killer fast.
2. To match against your buyer's GSTR-2. Mismatches trigger inquiries.

Think of GSTR-1 as your "outward sales declaration to the government." Get it wrong, three things suffer: your buyer's ITC, your GSTR-3B liability, and your future credit reputation.

2. GSTR-1 due dates for 2026

3. Late fees and consequences

The portal calculates late fees automatically the moment the deadline passes:

• Nil return: ₹50 per day (₹25 CGST + ₹25 SGST), capped at ₹500 per return per Act
• Other returns: ₹200 per day (₹100 + ₹100), capped at ₹10,000 per return per Act
• Indirect cost: Your buyer cannot claim ITC. They might delay your next payment.
• Compliance rating: GST portal tracks late filings; affects future audits
• Cannot file GSTR-3B: If GSTR-1 isn't filed, GSTR-3B for the same period is blocked

4. What you need before filing

Before you log in to the portal, gather:

1. All invoices raised in the period - invoice number, date, customer GSTIN/name, place of supply, taxable value, CGST/SGST/IGST amounts, HSN/SAC code
2. All credit notes and debit notes issued in the period
3. Export invoices with shipping bill number, port code, and date (if applicable)
4. HSN-wise summary of all outward supplies
5. Document numbers - invoices used, cancelled, missing (this is a separate table)
6. Login credentials: GSTIN, username, password, and OTP-receiving phone

5. Step-by-step portal walkthrough

Step 1: Login to gst.gov.in

Go to https://www.gst.gov.in. Click Login (top right). Enter your username and password. You'll receive an OTP on your registered phone - enter it.

Step 2: Open Returns Dashboard

Once logged in, click Services - Returns - Returns Dashboard. You'll see a list of returns to file.

Step 3: Select financial year and month

Pick the financial year (e.g., 2026-27) and the month or quarter you're filing for. The page will show a tile for GSTR-1 (Details of outward supplies of goods or services).

Step 4: Choose preparation method

Click PREPARE ONLINE if you have fewer than 500 invoices. For more, click PREPARE OFFLINE, download the offline tool, fill the Excel template, generate the JSON, and upload it back.

Step 5: Fill the tables (in order)

The portal shows tiles for each table. Fill them in this order - it's how the system validates internally:

1. B2B (Table 4) - invoices to GSTIN-registered buyers
2. B2CL (Table 5) - interstate B2C invoices > ₹2.5 lakh
3. B2CS (Table 7) - all other B2C, aggregated by state and rate
4. EXP (Table 6A) - export invoices (with LUT or with payment of IGST)
5. CDNR (Table 9B) - credit/debit notes against B2B invoices
6. CDNUR (Table 9B) - credit/debit notes against unregistered (B2C)
7. HSN summary (Table 12) - total outward supplies grouped by HSN/SAC
8. Documents issued (Table 13) - list of invoice numbers used, cancelled, etc.

Step 6: Verify totals

After filling each table, click SAVE. The portal recalculates totals. Compare them with your books - they must match exactly.

Step 7: Submit

Click SUBMIT. Once submitted, you cannot edit the return - only file or delete. Read the summary carefully.

Step 8: File with EVC or DSC

Click FILE GSTR-1. Choose:

• EVC (Electronic Verification Code) - OTP sent to authorised signatory's phone. For most freelancers and small businesses.
• DSC (Digital Signature Certificate) - required for companies and LLPs. Plug in your DSC token, enter PIN.

Once filed, you'll get an Acknowledgement Reference Number (ARN). Save it. Email yourself a copy.

6. The tables explained

7. The 7 most common GSTR-1 mistakes

1. Wrong tax type: Charging IGST when the customer is in the same state (should be CGST+SGST). Read our CGST vs SGST vs IGST guide
2. Wrong place of supply: For services, it's the customer's location, not yours. See place of supply rules
3. Missing HSN/SAC summary: Mandatory if turnover > ₹1.5 crore. Buyers complain to the gov when this is missing.
4. Late entry of credit notes: Issue a credit note in May? It must appear in May's GSTR-1, not later.
5. Forgetting export shipping bill details: EXP table without shipping bill number = system rejection.
6. Filing nil GSTR-3B but having GSTR-1 sales: The two must reconcile. Mismatch = notice.
7. Re-filing instead of amending: Once filed, you cannot re-file. Use Table 9 (amendments) in next month's GSTR-1.

8. Skip the manual data entry - auto-prep your ledger

Most of the time spent on GSTR-1 is not the portal. It's the data preparation: pulling invoices from Tally/Excel, splitting into B2B vs B2C, aggregating HSN, formatting state codes, etc. For a CA handling 30 clients, that's 4 hours of mind-numbing data entry per month per client.

Our Claude AI plugin auto-maintains a GSTR-1-ready ledger. Every invoice you raise gets appended to a CSV in the exact column structure the gst.gov.in portal expects:

v1.2 (released yesterday) also ships a one-click GSTR-1 portal-format JSON exporter. Run python scripts/gstr1_export.py --gstin YOUR_GSTIN --month 04-2026 and it generates a JSON in v3.1.6 format ready to upload to the GST portal's offline tool. 4 hours becomes 4 minutes.

9. Frequently asked questions