GST compliance in India has evolved significantly since the tax's rollout in 2017. In 2026, the return filing system has stabilised around a core set of forms — GSTR-1, GSTR-3B, and the annual GSTR-9 — with mandatory e-invoicing now covering businesses above ₹5 crore annual turnover and the threshold progressively lowering. For Kerala businesses — whether a Kochi trading firm, a Trivandrum-based IT service provider, or a Kozhikode spice exporter — GST compliance is now a monthly operational requirement that, if mismanaged, generates cascading penalties, blocked input tax credits, and supplier relationship problems. This guide is a practical operational reference, not a legal document — always verify current provisions with your CA or tax professional, as GST rules continue to be amended.
The Core GST Returns — Who Files What
GSTR-1 is filed by all regular registered taxpayers and reports all outward supplies (sales and export invoices, debit notes, credit notes) made during the month. Monthly filers must submit by the 11th of the following month. Quarterly filers under the QRMP scheme (Quarterly Return Monthly Payment, available to taxpayers with turnover up to ₹5 crore) submit by the 13th of the month following the quarter.
GSTR-3B is the monthly summary return filed by all regular taxpayers; it reports total outward supplies, input tax credit claimed, and tax paid. The due date is the 20th of the following month for Category 1 states — Kerala falls in Category 1, so GSTR-3B is due by the 20th. Category 2 and 3 states get extensions to the 22nd and 24th respectively.
GSTR-9 is the annual return reconciling the year's GSTR-1 and GSTR-3B filings. It is mandatory for taxpayers with turnover above ₹2 crore, and optional (though advisable) for turnover between ₹2 crore and ₹5 crore. The due date is 31st December of the following financial year — GSTR-9 for FY 2025–26 is due 31 December 2026.
GSTR-2B is NOT filed by taxpayers — it is auto-populated by the GST system showing the input tax credit available to you based on what your suppliers have filed in their GSTR-1. Reconcile your purchase records against GSTR-2B monthly before claiming ITC.
Additional special returns include GSTR-4 (annual return for composition scheme dealers), GSTR-5 (non-resident foreign taxable persons), GSTR-6 (input service distributors), GSTR-7 (entities required to deduct TDS under GST), and GSTR-8 (e-commerce operators such as Amazon and Flipkart).
GSTR-1 — Filing Your Outward Supplies
GSTR-1 must capture every invoice raised to a registered GST buyer (B2B invoice) and summaries of sales to unregistered buyers (B2C). For B2B invoices, you enter the buyer's GSTIN, invoice number, date, taxable value, and GST breakdowns — CGST plus SGST for intrastate transactions, and IGST for interstate transactions.
Each B2B invoice you report in GSTR-1 appears directly in your buyer's GSTR-2B. If you file late or incorrectly, your buyer loses ITC for that period, which damages your commercial relationship in ways beyond the immediate compliance issue.
Common GSTR-1 errors that create downstream problems:
- Wrong buyer GSTIN: verify against the GST portal before filing — an invalid GSTIN fails the return entirely.
- Incorrect HSN code: every B2B line item must carry the correct 4-digit or 8-digit HSN/SAC code; businesses above ₹5 crore turnover must use 6-digit HSN minimum.
- Wrong tax rate: a ₹1 lakh invoice filed at 12% instead of 18% creates a ₹6,000 ITC difference for your buyer and a tax liability gap for you.
- Missing credit notes: credit notes raised against previously filed invoices must be declared in GSTR-1 to cancel the original tax liability.
QRMP scheme taxpayers can use the Invoice Furnishing Facility (IFF) in months 1 and 2 of the quarter to report B2B invoices — this ensures buyers can claim ITC without waiting for the quarterly GSTR-1 filing deadline.
GSTR-3B — Monthly Tax Payment and Summary
GSTR-3B is where you actually pay GST. The process: calculate total output tax liability on all sales for the month; calculate eligible ITC from GSTR-2B and your own purchase records; net off ITC against output liability; pay the balance in cash via the electronic cash ledger on the GST portal.
ITC eligibility rules are frequently misunderstood. ITC is available only on goods or services used for business purposes. It is blocked on personal consumption, motor vehicles (passenger vehicles, unless in the transport or driving school business), food and beverages, club memberships, beauty treatment, health services, and construction of immovable property for personal use.
The 180-day rule catches many businesses off guard: if you do not pay your supplier within 180 days of the invoice date, the ITC you claimed on that invoice must be reversed in your GSTR-3B. Track supplier payment timelines and ensure all invoices are settled within 6 months of the invoice date.
On the provisional ITC rules: the 20% buffer rule was removed in 2022. You can now only claim ITC that actually appears in your GSTR-2B. Do not claim ITC on invoices that have not yet been filed by your supplier — it will be reversed upon reconciliation and create a cascading liability.
Recommended GSTR-3B filing sequence: file GSTR-1 first (by 11th or 13th), then check GSTR-2B after it populates on the 14th, then file GSTR-3B and pay any outstanding cash tax liability before the 20th.
E-Invoicing — Current Thresholds and Requirements
E-invoicing mandates that businesses above specified turnover thresholds generate all B2B invoices through the government's Invoice Registration Portal (IRP), which assigns a unique Invoice Reference Number (IRN) and QR code to each invoice before it is sent to the buyer.
Current threshold in 2026: mandatory for businesses with aggregate annual turnover above ₹5 crore in any preceding financial year from FY 2017–18 onwards. The government has signalled further lowering of the threshold — verify the current applicable threshold at einvoice1.gst.gov.in before assuming your business is exempt.
What e-invoicing means operationally: you cannot issue a regular Word or Excel invoice and manually enter it into GSTR-1. Your accounting or billing software must be integrated with the IRP API to generate a valid IRN-stamped e-invoice before the invoice reaches your buyer.
Compatible software options: Tally Prime (built-in IRP integration from version 3.0 onward); Zoho Books (built-in); Vyapar (built-in from recent versions); and custom ERP or billing systems (which must integrate with one of the approved IRP APIs). A critical clarification: e-invoicing does not mean emailing invoices. It means every B2B invoice receives an IRN from the IRP before dispatch.
Exemptions from e-invoicing: B2C invoices to unregistered buyers; export invoices (though many exporters generate e-invoices voluntarily to simplify customs clearance); banking institutions, insurance companies, NBFCs, and SEZ units.
Input Tax Credit Reconciliation — Monthly Discipline
ITC reconciliation is the most operationally important GST task for Indian businesses and the one most frequently neglected or performed incorrectly. When reconciliation is skipped month after month, the cumulative liability discovered during annual assessment can be significant.
The monthly reconciliation process:
- Download your GSTR-2B from the GST portal — available by the 14th of each month.
- Compare GSTR-2B entries against your purchase invoice register (the complete list of all invoices received and entered into your accounting system).
- Identify mismatches in three categories:
- Invoices in your purchase register but not in GSTR-2B: your supplier has not filed GSTR-1; you cannot legally claim ITC on these invoices until they appear. Follow up with the supplier immediately.
- Invoices in GSTR-2B but not in your purchase register: the supplier filed their return but you did not enter the invoice — locate and enter it to claim the available ITC.
- Invoices where the amount or tax differs between GSTR-2B and your records: this is a data entry error on either side; resolve with a credit note or an amended invoice from your supplier.
A practical note for Kerala businesses with multiple suppliers: if a supplier's invoices are consistently absent from your GSTR-2B, that supplier is either filing late or not filing at all. Beyond the ITC loss, this is also a commercial risk signal — a supplier with persistent GST non-compliance faces registration cancellation, which would disrupt your supply chain.
Penalties, Late Fees, and Interest
GST penalty and interest provisions as applicable in 2026 — always verify current rates as Union Budget amendments can change these figures:
Late filing of GSTR-1: ₹50 per day (₹25 CGST + ₹25 SGST) for returns with transactions; ₹20 per day (₹10 CGST + ₹10 SGST) for NIL returns. Maximum late fee: ₹10,000 per return (₹5,000 CGST + ₹5,000 SGST).
Late filing of GSTR-3B: same ₹50 per day structure, plus interest at 18% per annum on any unpaid tax calculated daily. If you owe ₹1 lakh in GST and pay 30 days late, the interest is ₹1,00,000 × 18% ÷ 365 × 30 = ₹1,479. Manageable in isolation, but if this recurs across multiple months and multiple heads of tax, the cumulative interest becomes a material liability.
Late filing of GSTR-9: ₹200 per day (₹100 CGST + ₹100 SGST), capped at 0.25% of turnover for the financial year.
Non-filing consequences: e-way bill generation is blocked after 2 consecutive missed returns; e-invoicing is blocked after defaults; GST registration is liable for cancellation after 6 consecutive missed returns for regular taxpayers. For product-based businesses in Kerala, blocked e-way bills mean you legally cannot transport goods above ₹50,000 value — which halts operations immediately.
If you have accumulated multiple unfiled returns, check GST.gov.in for any current amnesty scheme before paying the full accumulated late fee. The GST Council periodically announces reduced-fee windows for clearing backlogs, and these can substantially reduce your outstanding dues.
GST Compliance Calendar for Kerala Businesses
A monthly compliance calendar for a regular GST-registered business in Kerala (Category 1 state):
By the 11th of each month: file GSTR-1 reporting all sales invoices for the previous month. If above the e-invoicing threshold, all B2B invoices should already carry IRNs from the IRP — these feed directly into GSTR-1.
By the 14th: GSTR-2B is auto-populated by the GST system. Download it, reconcile against your purchase invoice register, and resolve any mismatches before GSTR-3B filing.
By the 20th: file GSTR-3B and pay any outstanding tax liability for the previous month using the electronic cash ledger on the GST portal.
Ongoing: maintain e-invoice generation for all B2B invoices if above the ₹5 crore threshold; keep your purchase invoice register updated in real time; follow up with suppliers whose invoices are absent from GSTR-2B.
For QRMP scheme taxpayers: file GSTR-1 by the 13th of the month following the quarter (or use IFF for B2B invoices in months 1 and 2 of the quarter). Pay GST via PMT-06 challan by the 25th of months 1 and 2 of the quarter — either a fixed amount or a self-assessed payment.
Annual: file GSTR-9 by 31st December for the previous financial year.
Kerala-specific compliance note: Kerala imposes the Kerala Flood Cess (KFC) — a 1% additional cess on most taxable supplies to consumers in Kerala (B2C transactions). This is separate from the standard GST and requires a distinct column in your invoice and a separate declaration in GSTR-3B. Businesses with operations in Kerala must confirm their billing software correctly handles KFC calculation and reporting — a gap here creates both compliance exposure and reconciliation problems.
Digital Tools for GST Compliance
Manual GST filing through the GST portal is error-prone and impractical for businesses with more than 20 to 30 invoices per month. The right accounting software pays for itself within the first month through time saved on data entry and errors avoided during reconciliation.
Tally Prime remains the dominant GST accounting software for Indian SMBs. It generates GSTR-1, GSTR-3B, and GSTR-9 reports directly from your transaction data and includes built-in e-invoicing integration and e-way bill generation. Annual licence cost: ₹18,000–₹27,000 depending on edition. For businesses that already use Tally for bookkeeping, upgrading to Tally Prime's GST-compliant version is the lowest-friction path to full compliance.
Zoho Books is a cloud-based accounting platform with full GST compliance built in. It is accessible from any browser and supports multiple user access — useful for businesses with remote teams or owners who want CA access without sharing a local system. Annual subscription: ₹9,000–₹25,000 depending on the plan and number of users.
Clear (formerly ClearTax) is a compliance-focused platform popular with chartered accountants managing multiple clients. It handles GSTR-1, GSTR-3B, GSTR-9, ITC reconciliation, and bulk filing — particularly useful if your CA manages your GST filings on your behalf.
Vyapar is a mobile-friendly billing and accounting application widely used among small traders and retail businesses in Kerala. It handles standard GST categories, e-invoicing, and e-way bill generation. A free tier is available; paid plans range from ₹4,000 to ₹8,000 per year. For a small Kochi retailer or a Thrissur wholesale trader with straightforward GST categories, Vyapar covers the basics effectively.
GST.gov.in (direct portal filing) is free and suitable for very small businesses with fewer than 10 invoices per month. For anything above that volume, the manual data entry burden and the absence of reconciliation assistance make it impractical as a sole compliance tool.
For Kerala businesses processing 50 or more invoices per month: the return on investment from paid accounting software is immediate. The time saved on data entry, the ITC recovered through proper reconciliation, and the late fees avoided through timely filing easily exceed annual software costs in the first quarter alone.
Frequently Asked Questions
What happens if I miss filing GSTR-1 or GSTR-3B for one month?
Missing one month triggers a late fee of ₹50 per day (₹20 per day for NIL returns) from the due date. For GSTR-3B, interest at 18% per annum accrues on any unpaid tax from the due date. More seriously, after 2 consecutive missed returns, your ability to generate e-way bills is blocked — which means you legally cannot transport goods above ₹50,000 value, effectively halting operations for product-based businesses. File the missed return as soon as possible, paying the accumulated late fee and any tax interest. If you have missed multiple months, check for any GST Council amnesty scheme that may have reduced the late fee — these are periodically announced and can significantly reduce the outstanding penalty.
Can I claim ITC on purchases made before GST registration?
Yes, with specific conditions and limits. A newly registered taxpayer can claim ITC on stock of inputs (raw materials and goods held for supply) held on the date immediately before the date of GST registration. You must file Form GST ITC-01 within 30 days of registration to claim this transitional ITC. ITC on capital goods — machinery, computers, vehicles used for business — is allowed subject to a reduction of 5% for every quarter from the original date of invoice. Inputs embedded in semi-finished or finished goods held in stock are also eligible. Inputs already consumed or goods already sold before the registration date are not eligible. This provision is particularly relevant for Kerala businesses that operate informally for some years before registering for GST when their turnover crosses the threshold or they decide to register voluntarily.
Is there any GST advantage to registering voluntarily if my turnover is below ₹20 lakhs?
Yes, in specific situations. Voluntary GST registration (below the mandatory ₹20 lakh threshold for most states, ₹10 lakh for special category states) makes commercial sense when you supply to GST-registered businesses who need to claim ITC on your invoices — unregistered suppliers block ITC for their buyers, making your services less commercially attractive; when you export goods or services and need to claim refund of ITC on inputs used in those exports; or when you plan to scale past the threshold within 12 months and want to establish a compliance track record. Disadvantages include monthly GSTR-1 and GSTR-3B filing obligations and accountant fees for compliance management. For Kerala freelancers and consultants whose clients are primarily GST-registered companies offering B2B services, voluntary registration often improves client win rates — registered clients prefer suppliers who provide GST invoices they can claim ITC on.