GST Return Filing Handbook 2026: Compliance Calendar

TL;DR

Every regular GST taxpayer files GSTR-1 by the 11th and GSTR-3B by the 20th each month. The annual GSTR-9 is due December 31, and GSTR-9C is required for turnover above ₹5 crore. Late fee under Section 47 runs ₹50 per day (₹20 per day for NIL), capped at ₹10,000 per Act. Interest under Section 50 runs 18% per annum on unpaid tax. The four returns serve different purposes. GSTR-1 feeds customers’ ITC claims. GSTR-3B triggers your tax payment. GSTR-9 reconciles the year. GSTR-9C bridges with the audit.

The 2026 Filing Calendar

The GST return filing calendar for a regular taxpayer (non-QRMP) follows a fixed monthly cycle. It also includes the annual return and (for turnover above ₹5 crore) the reconciliation statement.

Monthly cycle (12 times per year):

Day 1–10 of month M+1: Prepare GSTR-1 for month M.
Day 11 of month M+1: GSTR-1 due (13th for QRMP).
Day 12–13: GSTR-2B auto-generated from suppliers’ GSTR-1 filings.
Day 14–19 of month M+1: Prepare GSTR-3B for month M.
Day 20 of month M+1: GSTR-3B due (22nd–24th for QRMP).

Annual cycle (1 time per year):

December 31 of FY+1: GSTR-9 (annual return) due for the FY that just ended on March 31.
December 31 of FY+1: GSTR-9C (reconciliation statement) due if aggregate turnover during the FY exceeded ₹5 crore.

Quarterly cycle (composition scheme only):

18th of month following the quarter: CMP-08 due for the quarter.

Special-period returns:

GSTR-5 (non-resident): 20th of the month following the tax period.
GSTR-5A (OIDAR): 20th of the month following the tax period.
GSTR-6 (input service distributor): 13th of the following month.
GSTR-7 (TDS deductor): 10th of the following month.
GSTR-8 (TCS collector): 10th of the following month.

The due dates are fixed by Section 37 (GSTR-1), Section 39 (GSTR-3B), and Section 44 (GSTR-9). There is no relaxation for weekends or holidays. Late fee accrues every day, including non-working days.

What Each Return Captures

GSTR-1 — outward supplies register. Filed by every regular taxpayer. Captures every invoice. This includes B2B with customer GSTIN, B2C by state and rate, exports with shipping bill, advances, credit notes, and debit notes. HSN summary is in Table 12. Once filed, data flows into every supplier’s GSTR-2B within 24–48 hours. Customers can then claim ITC on what they bought from you.

GSTR-3B — summary self-assessment. The only return that triggers tax payment. Captures output tax, eligible ITC (auto-populated from GSTR-2B), ITC reversed under Rule 42 or 43, ineligible ITC under Section 17(5), and interest plus late fee. Net cash outflow equals output tax minus eligible ITC, plus interest and late fee. All paid via Electronic Cash Ledger.

GSTR-9 — annual reconciliation. A single-document reconciliation between the year’s GSTR-1 and GSTR-3B filings and the audited annual accounts. Tables 8 and 9 capture reversals and ITC claimed. Differences above ₹1 lakh per head attract notice under Section 73.

GSTR-9C — reconciliation statement. Required for turnover above ₹5 crore. Self-certified by the taxpayer (no expert certification needed since FY 2022-23, unless turnover exceeds ₹10 crore). Reconciles GSTR-9 with audited financial statements. Table 5 captures the reconciliations.

CMP-08 — composition quarterly statement. Filed by composition scheme taxpayers instead of monthly GSTR-1 or GSTR-3B. Captures turnover, tax payable at composition rate (1% for traders, 5% for restaurants), and any input used for ineligible purposes. Due on the 18th of the month following each quarter.

ITC Reconciliation Workflow

The most failure-prone part of monthly GST filing is ITC reconciliation between GSTR-2B and the purchase register. The workflow for our 12,000 or more monthly filings:

Day 1–3 of month M+1: data extraction. Pull all purchase invoices entered in Tally, Zoho Books, QuickBooks, or Busy during month M. The accounting system holds the invoices even if the supplier has not filed GSTR-1 yet. So the register is the source of truth for “what we bought”.

Day 4–7: GSTR-2B arrival. On day 13 of month M+1, the GSTN generates GSTR-2B for month M from suppliers’ GSTR-1 filings. We download the GSTR-2B JSON from the GST portal. We compare it line by line against the purchase register.

Day 8–10: reconciliation and supplier follow-up. For each purchase invoice in the register that does NOT appear in GSTR-2B, we:

Verify the supplier’s GSTIN is correct.
Check if the supplier has filed GSTR-1 for that period. Most missing invoices are from suppliers who have not filed yet.
Send a formal email reminder to the supplier with the invoice number and amount.
Flag invoices from suppliers who have stopped filing. This is a potential ITC blockage under Section 16(2).

The reconciliation typically recovers 5–15% of total ITC that would otherwise be lost. In one recent quarter, we recovered ₹14 lakh of ITC across 47 client filings. We did this by systematically chasing 200 or more suppliers. If that month-by-month cycle is the part you would rather not run yourself, our GST return filing service for Gujarat businesses files both returns and runs the same GSTR-2B reconciliation and supplier follow-up.

Day 11: GSTR-1 filing. Output side filed.

Day 12–18: GSTR-3B preparation. Open GSTR-2B in the GST portal. Apply ITC reversals under Rule 42 (for input services used partly for exempt supplies) and Rule 43 (for capital goods used partly for exempt supplies). Add ineligible ITC under Section 17(5). This includes motor vehicles, food and beverages, club membership, cosmetics, health and life insurance (with exceptions). Compute net tax. Generate the PMT-06 challan for the Electronic Cash Ledger.

Day 19–20: GSTR-3B filing. Top up the cash ledger via NEFT or RTGS one day before. Submit. ARN recorded.

Day 21–30: post-filing review. Respond to any officer queries under Section 61 (scrutiny). Manage refund claims if eligible. Update books with the actual cash outflow. Prepare ITC reversals for non-payment to suppliers within 180 days (Section 16(2)(b)).

Reverse Charge Treatment

Reverse charge under Section 9(4) shifts the GST payment obligation from the supplier to the recipient. The recipient includes the supply in GSTR-3B Table 3.1(d) and pays tax via cash ledger. The most common reverse-charge scenarios are:

Legal services from an advocate (Section 9(3) — irrespective of aggregate turnover).
Renting from an unregistered landlord for residential use (above ₹20,000 per month per individual agreement).
Goods transport agency (GTA) services from an unregistered transporter.
Services from a director or a related person (other than salary) where the supplier is not registered.
Import of services from a person outside India (Section 9(4) read with Section 13 — time of supply rules).

For each reverse-charge supply, the recipient self-invoices the supply (Section 31(3)(f)). They include the value in GSTR-3B Table 3.1(d). They pay tax in cash (no ITC on the cash payment, but ITC is available if the supply is for business use). They file GSTR-1 with reverse-charge details in Table 7C.

The reverse-charge workflow is integrated into the monthly GSTR-3B cycle. There is no separate return for it.

Late Fee and Interest Schedule

For FY 2025-26 (assuming no further amendment):

Return	Late fee per day	Cap (per Act per period)	Interest under Section 50
GSTR-1	₹50 (₹25 CGST + ₹25 SGST)	None specified (no cap)	n/a (no tax payment)
GSTR-3B	₹50 (₹25 CGST + ₹25 SGST)	₹10,000 per Act (₹20,000 total)	18% per annum on unpaid tax
GSTR-3B NIL	₹20 (₹10 CGST + ₹10 SGST)	₹5,000 per Act (₹10,000 total)	n/a (no tax)
GSTR-9	₹100 (₹50 CGST + ₹50 SGST)	0.25% of aggregate turnover	n/a (reconciliation only)
GSTR-9C	₹50 per Act	₹10,000 per Act	n/a
CMP-08	₹50 (composition)	₹5,000 per Act	18% per annum

The late fee cap for GSTR-3B of ₹10,000 per Act (₹20,000 combined CGST plus SGST for intra-State filers) was set by Notification 7/2023-CT. Before this notification, the cap was ₹5,000 per Act. So older returns (filed before July 2023) have a lower cap.

Interest under Section 50 starts accruing from the day immediately after the due date of payment till the day of actual cash ledger debit. For GSTR-3B unpaid tax of ₹10 lakh for 90 days, interest equals ₹10,00,000 times 18% times 90 divided by 365. That is ₹44,383.

Section 122 penalty (up to ₹10,000 per offence or amount of tax evaded, whichever is higher) applies only after a Show Cause Notice under Section 73 or 74, personal hearing, and order. For routine monthly late filings, the late fee plus interest is the standard exposure.

E-Invoicing and E-Way Bill

Two complementary electronic systems work alongside GSTR-1:

E-invoicing under Notification 13/2020-CT requires businesses with turnover above ₹5 crore to generate an IRN and QR code through the GSTN e-invoice portal for every B2B invoice. The threshold has dropped from ₹500 crore (FY 2020-21) to ₹5 crore (FY 2023-24). It may drop further. Below the threshold, e-invoicing is voluntary.

E-invoice data flows automatically into GSTR-1. This eliminates the need to manually upload invoices. The e-invoice portal pushes the data. The GSTR-1 form auto-populates from it. For businesses above the threshold, this is a significant time-saving.

E-way bill under Section 68 read with Rule 138 is required for every inter-State movement of goods of value exceeding ₹50,000. For intra-State movement, the threshold varies by State (₹50,000 in most, ₹15,000 in a few smaller States). The e-way bill is generated on the ewaybillgst.gov.in portal. It carries a unique 12-digit number. Validity depends on distance. 100 km equals 1 day for normal goods. 75 km equals 1 day for ODC (over-dimensional cargo). Extension is possible before expiry.

E-way bill is independent of GSTR-1. Both must be generated. Inconsistencies (e-way bill issued but no GSTR-1 invoice, or vice versa) trigger department notices.

The Seven Most Common Filing Errors

Based on FinTax24’s review of 12,000 or more monthly returns:

HSN code mismatch. Using 4-digit HSN when 6-digit is required (or vice versa) for the taxpayer’s turnover band. Since April 1, 2021, 6-digit HSN is mandatory for turnover above ₹5 crore.
Tax rate-versus-HSN mismatch. Charging 18% on a 12% HSN code (or 28% on an 18% code). The 12% slab was discontinued in the 2025-26 rationalisation. Many taxpayers have not updated their master data.
Inter-State versus intra-State confusion. Treating a supply as intra-State when the buyer is in a different State, or vice versa. This causes IGST versus CGST plus SGST mismatches.
ITC claimed on blocked items. Section 17(5) blocks ITC on motor vehicles, food, club, cosmetics, health insurance (with industry-specific exceptions).
Credit note timing. Issuing credit notes in a different period than the original invoice. This causes GSTR-1 mismatch.
Advance receipt treatment. Failing to declare advances against future supply. These are taxable at receipt under Section 12 for goods and Section 13 for services.
Late GSTR-2B reconciliation. Most practitioners download GSTR-2B but fail to reconcile it against the purchase register. The unreconciled invoices are then claimed or missed in subsequent months. This creates cumulative errors.

How FinTax24 Handles Monthly Filing

Our monthly process for a typical mid-size client (turnover ₹5–50 crore):

Day 1–3: Data extraction from accounting system plus manual entry collation.
Day 4–7: GSTR-2B reconciliation plus supplier follow-up emails (recoveries approximately 5–15% of ITC).
Day 8–10: GSTR-1 preparation and filing on day 11.
Day 12–18: GSTR-3B preparation plus GSTR-2B integration plus reversals plus cash ledger top-up.
Day 19–20: GSTR-3B filing.
Day 21–30: Post-filing review, refund management, supplier communication.

For clients above the e-invoice threshold, the IRN generation is integrated into the invoice creation in the accounting system. GSTR-1 auto-populates from the IRN data.

Frequently Asked Questions

What if I miss the GSTR-1 due date but file GSTR-3B on time?

You pay Section 47 late fee for the days GSTR-1 is delayed (₹50 per day, no cap). GSTR-3B can be filed independently. The GST portal does not block GSTR-3B for late GSTR-1. But the late GSTR-1 means your suppliers’ GSTR-2B is missing your invoices. Their ITC is wrong. Their GSTR-3B may be underpaid or over-claimed. The downstream impact is bigger than the late fee itself.

Can I revise a filed GSTR-1 or GSTR-3B?

GSTR-1 can be revised before the GSTR-3B due date (20th of the following month) using Amendment Table 9 or 10. GSTR-3B cannot be revised. Errors are corrected in the next month’s return (Table 4 for ITC, Table 5 or 6 for reversals). For substantive errors, an annual GSTR-9 revision is possible within the Section 44 window (currently December 31 of the following FY).

What happens if I claim ITC on an invoice whose supplier has not filed GSTR-1?

The auto-populated GSTR-2B excludes the supplier’s invoice. If you claim ITC on an invoice not in GSTR-2B, the credit may be reversed under Section 16(2)(c) on audit. The proper workflow: chase the supplier to file GSTR-1 first. Then claim ITC the following month when the invoice appears in your GSTR-2B.

Can I claim ITC on a credit note issued to me?

Yes. The supplier’s credit note appears in your GSTR-2B Table 3 (negative entry). This reduces your eligible ITC the following month. The timing aligns with the supplier’s filing of GSTR-1 with the credit note.

What is the difference between Section 73 and Section 74?

Section 73 covers non-fraud cases. These include late filing, short-payment, and excess ITC claim. The penalty is 10% of the tax short-paid. Section 74 covers fraud cases. These include wilful mis-statement, suppression of facts, and invoices without supply. The penalty is 100% of the tax short-paid. Standard late filing plus interest under Sections 47 and 50 falls under Section 73, not Section 74.

How do I handle e-invoice errors after filing?

E-invoice errors (wrong GSTIN, amount, HSN) can be corrected by cancelling the original IRN within 24 hours (before GSTR-1 filing) and issuing a new invoice with a fresh IRN. After GSTR-1 is filed, the only correction path is via Amendment Table 9 of the next GSTR-1. Or GSTR-9 reconciliation at year-end.

Can I use the QRMP scheme mid-year?

The QRMP (Quarterly Return Monthly Payment) scheme requires an opt-in declaration in Form GST REG-01 (or amendment via GST REG-02) at the start of a quarter. Once opted in, you cannot switch back to monthly filing for that quarter. The scheme applies to small taxpayers with turnover up to ₹5 crore.

What is GSTR-2B and how is it different from GSTR-2A?

GSTR-2A is a dynamic statement that updates as your suppliers file GSTR-1 throughout the month. GSTR-2B is a static statement generated on the 13th of the following month. It locks in the supplier data for ITC claims. You should claim ITC based on GSTR-2B, not GSTR-2A. This is because GSTR-2B is the version the system uses for GSTR-3B auto-population.

How to Get Started

For first-time filers, the GST Registration service sets up your GSTIN in 3–5 working days. For ongoing monthly filing, the GST Return Filing service handles both GSTR-1 and GSTR-3B. It includes full ITC reconciliation, supplier follow-up, and an annual GSTR-9.

For e-invoice enabled businesses, the workflow integrates with Tally, Zoho Books, or QuickBooks. It pushes IRN generation directly from your accounting system. For e-way bill, the FinTax24 portal integration pushes e-way bill generation alongside your GSTR-1 filing. The two are always consistent.

Talk to our indirect-tax desk for a free 30-minute consultation. We will cover which return types apply to your business, what your ITC recovery opportunity is, and the typical compliance cost for your turnover band.