How to Log In and File GSTR One Step by Step in 2026

GST Login & GSTR One Filing Step-by-Step Guide 2026

Quick Overview

GSTR One is your outward supplies return. The first return in the GST filing cycle. Every invoice you issue goes here. Your buyer's GSTR TwoA is auto-populated from your GSTR One, so accuracy matters.

Filing Deadlines 2026:

• Monthly Filers: 11th of next month
• Quarterly Filers (QRMP): 13th of month after quarter ends

Estimated Reading Time: 25 minutes | Difficulty: Easy for freshers, routine for professionals

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Step 1: GST Portal Login - Complete Instructions

Before You Start

Have ready:

• Your 15-digit GSTIN (Goods and Services Tax Identification Number)
• Registered email address or User ID
• Your GST portal password
• 2FA mobile number linked to your GSTIN

How to Log In to GSTN Portal

1. Visit the GST Portal

   • Go to www.gst.gov.in in your web browser
   • Click "Login" in the top-right corner

2. Enter Your Credentials

   • GSTIN/UIN: Enter your 15-digit GSTIN (the unique ID assigned after GST registration)
   • User ID: Enter your registered email address or custom User ID
   • Password: Enter your GST portal password

3. Two-Factor Authentication 2FA)

   • The portal sends an OTP (One-Time Password) to your registered mobile number
   • Enter the 6-digit OTP in the prompt box
   • Click "Submit" or "Verify"

4. Dashboard Access

   • Once verified, you'll see your GST Dashboard
   • Look for "Services" or "File Return" menu on the left sidebar
   • Select "File GSTR One" to begin

Forgot Your Password?

1. On the login page, click "Forgot Password"
2. Enter your GSTIN or User ID
3. Verify via OTP sent to registered mobile
4. Create a new strong password (min 12 characters with numbers & symbols)
5. Click "Update Password" and log in with new credentials

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Step 2: Navigate to GSTR One Filing Section

Once logged in:

1. From dashboard, click "Services" (left sidebar)
2. Select "Returns" → "File GSTR One"
3. Choose Assessment Year (e.g., 2026-27 for FY 2025-26)
4. Click "Prepare Offline" or "File Now" depending on your data readiness

Pro Tip for Freshers: If you have many invoices, use "Prepare Offline" to fill in Excel, then upload bulk. For small businesses (< 50 invoices), fill directly online.

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Step 3: Understanding GSTR One Tables & Tabs

GSTR One has 13 tables. Not all apply to your business. Here's a quick guide:

Business Type & Applicable Tables

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Step 4: How to Fill GSTR One (Line-by-Line Instructions)

For B2B Invoices (Table 4A - Most Common)

Example Calculation 18% GST)

Scenario: You sold goods to another registered business:

• Invoice Value: Rs. 10,000
• HSN Code: 6204 (Garments)
• Within same state (Telangana)
• GST Rate: 18%

How to Fill:

• Invoice Amount: Rs. 10,000
• Taxable Amount: Rs. 10,000
• SGST: Rs. 900 10,000 × 9%)
• CGST: Rs. 900 10,000 × 9%)
• IGST: Rs. 0 (not applicable for intra-state)
• Total Tax: Rs. 1,800
• Final Invoice to Customer: Rs. 11,800 10,000 + 1,800)

What If Buyer Doesn't Have GSTIN?

Use Table 4B (B2B with missing GSTIN):

• Enter invoice details same as Table 4A
• GSTIN field: Leave blank or enter "UNREGISTERED"
• GST treatment: Same as Table 4A (you still charge GST)
• Risk: No ITC benefit for buyer; may attract GST notice

Tip: Always request GSTIN from buyers. If they're registered and claim no GSTIN, flag it.

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Step 5: HSN Code Selection (Critical for Compliance)

Why HSN Codes Matter

✅ Affects your GST audit: Mismatched HSN codes trigger Department queries ✅ Determines ITC eligibility: Buyer needs matching HSN to claim ITC ✅ Tax rate verification: Wrong HSN = wrong tax rate = penalties

How to Find Your HSN Code

Method 1: Official GST Portal Search

1. Go to www.gst.gov.in
2. Click "Services" → "Search" → "Search HSN Code"
3. Enter your product description (e.g., "Ladies Trousers", "Software Development")
4. Portal returns 6-digit code, description, and applicable GST rates
5. Copy the code; use it in Table 12 (HSN Summary)

Method 2: Common HSN Codes by Business Type

Pro Tip: Document your HSN code once. Use it consistently across all invoices. If product changes, update HSN.

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Step 6: Table 12 - HSN Summary (Aggregate View)

What is Table 12? Sum of all HSN codes used across Tables 4A, 5B, 5C, etc. Portal auto-calculates this when you add line items.

Example for Multi-Product Business:

The portal auto-populates Table 12 from your individual entries. No manual action needed unless you spot errors.

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Step 7: Upload & File Your GSTR One

Option A: Direct Online Filing (Small Businesses)

1. Fill all tables directly in portal
2. Review each entry for accuracy
3. Click "Save" → "Submit"
4. Generate "Provisional ID" (PRN) - save this
5. Done - Filing complete within 2 minutes

Option B: Offline File Upload (Large Businesses)

For businesses with 100+ invoices:

1. Download "Excel Template" from portal
2. Fill invoice details in Excel (one row = one invoice)
   • Column A: Invoice No.
   • Column B: Invoice Date
   • Column C: GSTIN
   • ... (same columns as Table 4A)
3. Save as .csv or .xlsx
4. Go to portal → "Upload"
5. Select your file → "Validate"
6. Fix any errors shown in validation report
7. Re-upload corrected file
8. Click "Submit" once validation passes

Validation Checks Before Submitting

✓ All GST rates correct for product/service
✓ HSN codes match your business type
✓ Invoice dates fall within the filing period 1st to last date of month)
✓ GSTIN format correct 15 digits, no spaces)
✓ Tax calculation correct (no manual math errors)
✓ Credit/Debit notes linked to original invoices

Pro Tip: If system shows "No errors", take a screenshot before submitting. File in portal always keeps a copy, but your backup helps with reference.

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Step 8: After Filing - What Happens Next?

Timeline

Deadline Timeline

Post-GSTR One Filing: What Happens Next

Your filing triggers a chain of events in the GST ecosystem

1. Day 0

   GSTR One Filed

   PRN generated. Status on dashboard changes to Filed. Acknowledgment sent to registered email.

2. Day 1-2

   System Validates Entries

   GSTN handles GSTIN formats, HSN codes, tax calculations. Errors appear in Messages section of dashboard.

3. Day 2-10

   Buyers' GSTR TwoA Updated

   All your B2B invoices appear in your buyers' GSTR TwoA. They can view and match against their purchase register.

4. By 13th

   GSTR OneA Amendment Window Open

   Use GSTR OneA to add omitted invoices or correct errors before GSTR ThreeB deadline.

5. 20th

   GSTR ThreeB Deadline

   File GSTR ThreeB and pay net GST due. Uses the outward supply data from your GSTR One.

Source: GST return filing cycle, CGST Rules 2017

If You Make a Mistake After Filing

✓ Can amend: Use "GSTR OneA" to add/modify invoices (file anytime before GSTR ThreeB deadline)
✗ Cannot change: Cannot delete already-filed invoices in original GSTR One

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Step 9: Common Mistakes & How to Avoid Them

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Checklist: Before You File GSTR One

• All invoices issued in the period accounted for
• Buyer GSTIN verified 15 digits, format: XX000XXXXXOXZ)
• HSN codes selected for all products/services
• Tax rates verified against current GST 2.0 slabs 5%, 18%, 40%; 0%, 0.25%, 3% for specific goods; 0% for zero-rated)
• Credit/Debit notes linked to original invoices
• Export invoices marked with Shipping Bill No. (if applicable)
• B2C sales aggregated by tax rate (not individual line items)
• No duplicate invoices listed
• Portal login working; password reset done if needed
• Offline file validated before upload (if uploading Excel)

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FAQ - GSTR One Filing

Q: Can I file GSTR One late?
A: Yes, but Rs. 50/day late fee applies (Rs. 25 CGST + Rs. 25 SGST) up to capped amount. File within 11 days of month-end to avoid.

Q: What if my buyer doesn't have GSTIN?
A: They're likely unregistered (turnover < Rs. 40 lakh). File in Table 4B. They can't claim ITC. Some states/businesses must register even below threshold. Flag for verification.

Q: How do I amend a filed GSTR One?
A: Use GSTR OneA (amendment form). Add missing invoices or correct amounts. File before month-end of next month.

Q: What's HSN code for services?
A: Services are 5-digit SAC codes, not HSN. Example: SAC 6202 for consulting. GST portal searchable under "SAC Code" tab.

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Next Steps

✅ Filed GSTR One? Now file GSTR Two (purchases) by month-end
✅ Reconcile with buyer's GSTR ThreeB
✅ File GSTR ThreeB by deadline 20th for monthly filers)
✅ Make GST payment on same day

Need help? Contact us via WhatsApp or email. We handle GSTR One filing for 500+ businesses monthly, checked for common errors before submission.