Every month, lakhs of Indian businesses scramble to file GST returns before the deadline. GSTR-1 data is incomplete. GSTR-3B liabilities do not match. ITC claims get rejected. And the 20th of every month becomes a stress test for every CA firm in the country.
This does not have to be your reality. If you understand the GST filing process clearly — what goes where, what feeds into what, and what the common failure points are — filing becomes a structured process instead of a panic.
GST Return Filing: The Big Picture
India’s GST return system has multiple forms, but for most regular taxpayers, two returns matter every month (or quarter):
| Return | What It Covers | Due Date | Who Files |
|---|---|---|---|
| GSTR-1 | All outward supplies (sales) | 11th of next month | Regular taxpayers |
| GSTR-3B | Summary return (tax liability + ITC claim) | 20th of next month | Regular taxpayers |
There are also annual returns (GSTR-9) and other forms, but this guide focuses on the monthly cycle that every business must follow.
GSTR-1: Outward Supplies Return
GSTR-1 is where you report every sale you made during the period. Every invoice, every credit note, every export.
What Goes into GSTR-1
GSTR-1 is organized into several tables:
B2B Invoices (Table 4A)
- All invoices where the buyer is GST-registered
- Must include: buyer GSTIN, invoice number, date, taxable value, CGST, SGST, IGST, place of supply
B2C Large (Table 4B)
- Inter-state (different state) B2C invoices above Rs. 2.5 lakhs
- Listed individually
B2C Small (Table 5)
- All other B2C invoices
- Reported as consolidated summaries by rate and state
Credit/Debit Notes (Table 9B)
- All credit notes and debit notes issued during the period
HSN Summary (Table 12)
- Total value and tax grouped by HSN/SAC code and tax rate
Step-by-Step GSTR-1 Filing
- Verify your invoices: Every invoice issued during the period has correct GSTIN, HSN, tax rates, and amounts
- Compile B2B data: List all B2B invoices with full details
- Compile B2C data: Summarize B2C invoices by tax rate and state
- Add credit/debit notes: Include all adjustments
- Generate HSN summary: Group by HSN code and rate
- Upload to GST portal: Enter data or upload JSON
- Preview and verify: Cross-check totals with your books
- Submit and file: E-verify using DSC or OTP
Common GSTR-1 Errors
- Wrong GSTIN: A single wrong digit makes the buyer’s ITC claim fail
- Missing invoices: Forgetting to include an invoice means unreported sales
- Wrong tax type: CGST/SGST instead of IGST for inter-state sales
- Incorrect HSN codes: Wrong classification leads to wrong tax rates
- Invoice number gaps: Unexplained gaps attract scrutiny during audits
- Missing credit notes: If you issued credit notes, they must be reported
GSTR-3B: Summary Return
GSTR-3B is a self-declared summary return. You report your total tax liability and claim Input Tax Credit (ITC). It is not auto-populated from GSTR-1 (unlike the original GSTR-3 design) — you fill it manually.
What Goes into GSTR-3B
Table 3.1: Outward Supplies and ITC
- (a) Outward taxable supplies (other than zero-rated and nil-rated)
- (b) Outward zero-rated supplies (exports)
- (c) Other outward supplies (nil-rated, exempt)
- (d) Inward supplies liable to reverse charge
- (e) Non-GST outward supplies
Table 4: Eligible ITC
- (A) ITC available (including reverse charge)
- (B) ITC reversed (ineligible credit)
Table 5: Exempt and Nil-Rated Supplies
Table 6: Payment of Tax
- Tax paid through ITC
- Tax paid in cash
Step-by-Step GSTR-3B Filing
- Calculate total outward liability: Sum up CGST, SGST, IGST from all sales (should match GSTR-1)
- Calculate eligible ITC: From all purchase invoices where supplier has filed GSTR-1
- Apply ITC correctly: CGST ITC offsets CGST liability, SGST ITC offsets SGST, IGST offsets IGST
- Set off tax in correct order: IGST first, then CGST/SGST
- Pay remaining balance: Through cash ledger (online payment)
- Verify before submission: Ensure liability matches your books
The ITC Set-Off Order (Critical)
This is where most errors happen. The order of set-off is prescribed by law:
- IGST ITC → can offset IGST, then CGST, then SGST (in that order)
- CGST ITC → can offset CGST only
- SGST ITC → can offset SGST only
Example:
- IGST liability: Rs. 50,000
- CGST liability: Rs. 30,000
- SGST liability: Rs. 30,000
- IGST ITC available: Rs. 60,000
- CGST ITC available: Rs. 25,000
- SGST ITC available: Rs. 25,000
Set-off:
- IGST ITC (Rs. 60,000) → offset IGST liability (Rs. 50,000). Remaining IGST ITC: Rs. 10,000
- Remaining IGST ITC (Rs. 10,000) → offset CGST (Rs. 10,000). Remaining CGST: Rs. 20,000
- CGST ITC (Rs. 25,000) → offset remaining CGST (Rs. 20,000). Remaining CGST ITC: Rs. 5,000
- SGST ITC (Rs. 25,000) → offset SGST (Rs. 25,000). Remaining SGST: Rs. 5,000
- Cash payment: Rs. 5,000 (SGST)
Due Dates for 2026
| Month | GSTR-1 Due | GSTR-3B Due |
|---|---|---|
| April 2026 | 11 May | 20 May |
| May 2026 | 11 June | 20 June |
| June 2026 | 11 July | 20 July |
Quarterly filers (QRMP scheme): File GSTR-1 quarterly, GSTR-3B quarterly, but pay tax monthly via challan.
How to Ensure GST Filing Is Always Accurate
The core problem with GST filing in India is not complexity — it is data quality. If your invoices are recorded correctly throughout the month, filing is a matter of compiling the data.
During the Month
- Record every invoice with correct GSTIN, HSN, tax type, and amounts
- Verify purchase invoices against supplier GSTR-1 (ITC matching)
- Reconcile bank statements to ensure all payments and receipts are captured
- Record credit notes and debit notes as they happen
Before Filing
- Cross-check GSTR-1 data against your books (total sales should match)
- Verify ITC eligibility — supplier must have filed GSTR-1
- Reconcile GSTR-2B (auto-populated ITC data) with your purchase register
- Calculate tax liability and ensure cash ledger has sufficient balance
How This Works in Practice
Most CAs and businesses follow a monthly rhythm:
- 1st-10th: Collect data from clients, verify invoices, prepare GSTR-1
- 11th: File GSTR-1
- 12th-18th: Match ITC with GSTR-2B, prepare GSTR-3B
- 19th-20th: File GSTR-3B
The problem is that if invoicing was not done properly during the month, days 1-10 become chaos — re-entering data, fixing errors, chasing clients for GSTINs.
With a System Like Hisaabo
Instead of month-end panic, the workflow becomes:
- All invoices recorded with correct GST data throughout the month
- GSTR-1 and GSTR-3B reports generated from your invoice data automatically
- ITC matching done continuously, not at month-end
- File directly from the system — data is already structured correctly
The key insight: GST filing should be the last step, not the first. If your accounting system enforces correct GST data at the invoice level, the return is a report — not a project.
Frequently Asked Questions
What happens if I file GSTR-1 late?
Late filing attracts a penalty of Rs. 50 per day (Rs. 20 for nil return). Interest also applies on any tax liability.
Can I revise GSTR-1?
No. GSTR-1 cannot be revised once filed. Corrections are made in the next period’s return.
What is the difference between GSTR-2A and GSTR-2B?
GSTR-2A is a dynamic view of all inward supplies (auto-populated from suppliers’ GSTR-1). GSTR-2B is a static, finalized version generated for each period. Use GSTR-2B for ITC claims.
What if my supplier has not filed GSTR-1?
You cannot claim ITC on invoices where the supplier has not filed GSTR-1. This is the single biggest reason for ITC rejection. Regularly check GSTR-2B and follow up with suppliers.
What is the QRMP scheme?
Quarterly Return Monthly Payment. Businesses with turnover up to Rs. 5 crore can file GSTR-1 and GSTR-3B quarterly but must pay tax monthly via challan (self-assessed).
If your GST filing process involves month-end data entry marathons, something is broken upstream. Fix your invoicing and reconciliation during the month, and filing becomes a 20-minute task.