GST has been the law of the land for nearly a decade now. Yet, the compliance notices have not slowed down. If anything, the frequency of scrutiny has grown sharper. In FY 2024–25 alone, over 33,000 compliance notices were issued by the GSTN. The reason, in most cases, was not fraud or deliberate evasion - it was a string of avoidable procedural errors that quietly accumulated over months.
The GST system today is not the same as it was in 2017. The portal uses AI-powered data matching, invoice-level reconciliation, and real-time analytics. A mismatch that once may have gone unnoticed for a quarter now triggers an automated notice within days. For any business owner or finance team that relies on manual processes or last-minute filing habits, this environment carries very real financial risk.
At CA Pramod Singhal, we have worked with 500+ clients across India and guided over 300 businesses through the 2017 GST migration. Over the years, a set of recurring mistakes surfaces across virtually every type of entity - startups, SMEs, trading firms, and service providers alike. This blog post covers the most consequential ones, and more importantly, what can be done to prevent them.
What are GST Compliance Mistakes?
GST compliance mistakes are procedural or reporting errors made during return filing, ITC claims, or tax payments that violate India's GST regulations. These include GSTR-1 and GSTR-3B mismatches, wrongful input tax credit claims, missed deadlines, and reverse charge non-compliance, often resulting in penalties, notices, or blocked credits from the GSTN.
8 GST Compliance Mistakes That Cost Indian Businesses Every Year
1. Mismatch Between GSTR-1 and GSTR-3B
This is the single most flagged issue by the GSTN system. GSTR-1 captures your invoice-wise outward supplies, while GSTR-3B is the monthly summary return where you declare total tax liability and claim input credit. When the numbers in both do not match, the portal raises a flag immediately - no manual intervention needed. The mismatch usually creeps in when sales data lives in two places at once: an accounting software and a separate spreadsheet, each updated at different times.
Invoices entered after the GSTR-1 cutoff but included in GSTR-3B create a gap the portal detects automatically.
Sales reported higher in GSTR-1 than GSTR-3B signals an underpayment, triggering automated tax demand notices quickly.
Your buyers' ITC claims get blocked when your return data doesn't match what shows in their GSTR-2B.
Data maintained across two separate systems - software and spreadsheets - is the root cause behind most mismatches.
A single missed reconciliation between your sales register and GSTR-1 can set off a chain of compliance issues.
CA Pramod Singhal runs a monthly reconciliation check across all client filings, catching GSTR-1 and GSTR-3B gaps well before portal scrutiny begins.
Fix: Reconcile your sales register with GSTR-1 before filing GSTR-3B every month without exception. If you handle multiple GST registrations or operate across branches, invest in a consolidated view that reduces the chance of data being entered twice in different formats.
2. Claiming ITC Without Reconciling GSTR-2B
ITC is valuable - but claiming it without checking GSTR-2B is where businesses get hurt. GSTR-2B is the static monthly statement the portal generates based only on what your suppliers have actually filed. If a vendor skips their GSTR-1 or uploads an invoice with a wrong GSTIN, that credit simply does not show up in your GSTR-2B. Claiming it anyway means claiming something the system has not validated - and it gets reversed with interest. From October 2025, the Invoice Management System tightened this further, making unaccepted invoices invalid for ITC entirely.
Supplier non-filing blocks your credit: if your vendor has not filed GSTR-1 that month, the ITC does not appear in your GSTR-2B at all.
Wrong GSTIN on an invoice means the credit never reaches your GSTR-2B, even if the purchase is completely legitimate and genuine.
Claiming unvalidated ITC gets reversed with interest, turning a working capital benefit into a direct and avoidable financial liability.
Post-October 2025 IMS rules treat unaccepted invoices as invalid, so any credit claimed on them is automatically disallowed by the portal.
The verification burden now sits with the recipient, meaning you must confirm supplier compliance before claiming any input credit each month.
CA Pramod Singhal matches every client's purchase register against GSTR-2B each month, so only validated credits get claimed and reversals stay at zero.
Fix: Always use GSTR-2B - not GSTR-2A - as your base document when finalising ITC for the month. Match your purchase register against it, and claim only what is reflected. For high-volume businesses with multiple vendors, monthly reconciliation is not optional; it is a protection against working capital disruption.
3. Late Filing of Returns - and Why "Just a Few Days" Adds Up
Late filing of GSTR-1, GSTR-3B, or GSTR-9 is one of the most common mistakes across businesses of every size. The late fee on GSTR-3B starts at ₹50 per day and runs until the return is filed - nil returns are capped at ₹500, but anything with liability keeps accumulating. What makes this worse is that GST return timelines are sequential. A pending return from one month blocks the next, and backlogs compound fast. A two-week slip in April can quietly turn into a multi-month problem by June.
GSTR-3B late fee runs daily: ₹50 per day with no upper cap for returns that carry an actual tax liability.
Nil return cap at ₹500: even with no liability, delayed filing still attracts a fee that adds up across registrations.
Pending GSTR-3B blocks e-way bills: businesses that move goods regularly can face a full operational halt until the return clears.
Repeated late filings build a scrutiny trail: authorities treat consistent defaulters very differently from businesses that missed one deadline.
Sequential return timelines mean backlogs compound: you cannot file a later period without clearing all earlier pending returns first.
CA Pramod Singhal manages the full return calendar for every client, making sure no deadline is missed and no backlog gets a chance to build.
Fix: Maintain a GST compliance calendar with all due dates marked well in advance. Close your books monthly - not quarterly. A firm like CA Pramod Singhal manages the full return lifecycle for clients to ensure zero missed filings, which reflects in the firm's 100% compliance record over two decades of practice.
4. Incorrect or Missing HSN/SAC Codes
Every good and service under GST must carry the right HSN or SAC code - these codes determine the tax rate that applies. Using a wrong code, even if the rate itself is correct, gets flagged in automated scrutiny and disrupts your buyer's ITC reconciliation. The GST Council revises HSN classifications periodically, so a code that worked in 2021 may not be valid today. For businesses above ₹5 crore turnover, e-invoicing has been mandatory since April 2025 - and an invalid HSN code causes the IRP to reject the invoice outright, with no IRN generated and no ITC for the buyer.
Wrong HSN despite correct tax rate: automated scrutiny flags the code mismatch regardless, and your recipient's ITC reconciliation gets affected directly.
Outdated codes from older systems: manually generated invoices or un-updated software often carry HSN codes that no longer reflect current GST Council classifications.
Periodic GST Council revisions change classifications: a code accurate in 2021 may map to a different rate or category under today's schedule.
E-invoice rejection at IRP: an invalid HSN on an e-invoice means no IRN is generated and the entire document is treated as invalid.
Buyer loses ITC on rejected invoices: when your e-invoice fails at the portal, your buyer cannot claim input credit on that purchase at all.
CA Pramod Singhal reviews HSN and SAC codes across all client invoices each year, ensuring every code reflects the latest CBIC classifications before filing begins.
Fix: Build a master list of HSN/SAC codes for all your goods and services. Review it at the start of each financial year after checking the latest CBIC rate notifications. If your business spans multiple product categories, this is an area where a periodic review with your tax advisor can prevent significant downstream problems.
5. Non-Compliance with Reverse Charge Mechanism (RCM)
Under RCM, the recipient pays GST directly to the government - not the supplier. Legal services, GTA services, imported services, and commercial rent from unregistered landlords all fall under this. Missing an RCM transaction means you owe the tax plus 18% interest per annum from the date it was due. On top of that, RCM liability must be paid in cash through the cash ledger - ITC cannot be used to discharge it. There is also a self-invoicing requirement when buying from unregistered suppliers, which most businesses either miss entirely or handle incorrectly.
Not knowing RCM applies: many businesses process legal, transport, or import transactions without realising GST liability sits with them, not the supplier.
Unreported RCM in GSTR-3B: knowing RCM applies but skipping the disclosure in GSTR-3B is treated as non-payment and attracts immediate interest.
Interest at 18% per annum: the moment RCM goes unpaid, interest starts running from the original due date with no grace period whatsoever.
Cash ledger mandatory for RCM: input tax credit cannot be used to settle reverse charge liability - it must be paid in cash only.
Missing self-invoice for unregistered suppliers: buying under RCM requires a self-invoice on the supplier's behalf, correctly tagged and disclosed in GSTR-3B separately.
CA Pramod Singhal maintains a transaction-level RCM register for every client, making sure every liability is identified, self-invoiced, and discharged correctly each month.
Fix: Maintain a register of all transactions that fall under RCM. If you use GTA services, legal consultants, or have any cross-border service imports, verify applicability each time. The list of notified RCM categories changes periodically - the most recent updates from January 2025 removed sponsorship services from RCM, which means businesses that were paying under RCM for that category needed to update their process.
6. Claiming Blocked Credits Under Section 17(5)
Section 17(5) blocks ITC on motor vehicles, construction, food, beauty treatments, and club memberships - even when the invoice exists and tax was paid. Without a category filter in your purchase process, these slip into your ITC claim. Erroneous claims attract 18% interest; fraudulent ones reach 24%.
Motor vehicles for personal use: GST paid on cars or two-wheelers used outside business purposes is fully blocked under Section 17(5).
Construction of immovable property: input credit on building or civil work is not available, even when the property is used for business operations.
Food, beverages, and beauty treatments: GST on staff meals, canteen expenses, or salon services cannot be claimed as input credit under any circumstance.
Club memberships and personal consumption: any purchase that serves personal use rather than business operations falls squarely under the blocked credit list.
No ITC filter in accounts payable: without a dedicated check, blocked category purchases pass through the purchase register and enter ITC claims undetected.
CA Pramod Singhal runs a category-level blocked credit check across every client's purchase data, making sure Section 17(5) items never make it into an ITC claim.
Fix: Create a category-level filter in your accounts payable process that flags any purchase falling under Section 17(5). This is particularly important when your business has employee-related expenses, transportation, or construction activity running simultaneously with regular GST operations.
7. Failing to Update the GST Profile After Business Changes
A GSTIN must reflect your business as it actually runs - not just at registration. Address shifts, new branches, partner additions, and signatory changes all need portal updates. An outdated registration causes problems during audits, refund claims, and e-invoice generation. Dormant GSTINs without cancellation keep attracting late fees.
New branch not added to registration: opening an additional place of business without updating the GST portal creates a compliance gap during audits.
Address change not amended on portal: operating from a different location than what the registration certificate shows flags discrepancies during refund processing.
Authorised signatory not updated: an outdated signatory on record creates authentication issues with return filing, e-invoicing, and official GST correspondence.
Partner or director addition skipped: core amendments like adding partners or directors must go through the prescribed portal process, not just internal business records.
Inactive GSTIN without cancellation: a dormant registration with no filed returns keeps accumulating late fees and can attract demand notices despite zero actual liability.
CA Pramod Singhal conducts an annual GST registration review for every client, making sure the profile on record matches the business as it actually stands today.
Fix: Review your GST registration certificate at least once a year. Any change in business structure, location, or key personnel should trigger an immediate update on the portal. If the business is winding down or going dormant, apply for cancellation promptly rather than allowing returns to lapse.
8. Skipping the Annual Return (GSTR-9) or Filing It Without Reconciliation
GSTR-9 pulls together every GSTR-1 and GSTR-3B filed through the year and confirms ITC was claimed, reversed, and discharged correctly. Mandatory above ₹2 crore turnover, with GSTR-9C required above ₹5 crore. Errors carried forward from monthly returns - wrong HSN codes, missed RCM, unreconciled ITC - surface here. Missing the December 31 deadline costs ₹200 per day.
Treating GSTR-9 as a formality: carrying monthly figures forward without verification means accumulated errors land directly in the annual return unaddressed.
Wrong HSN codes across monthly returns: incorrect classifications filed month after month show up consolidated in GSTR-9 and create a much larger correction burden.
Unreconciled ITC in annual return: any input credit claimed but not properly matched through the year gets flagged during GSTR-9 reconciliation without exception.
Missed RCM liabilities surface in GSTR-9: reverse charge obligations skipped during monthly filings become visible and undeniable when the full year is reviewed together.
Late filing penalty at ₹200 per day: missing the December 31 deadline accumulates fees daily, capped at 0.25% of your total annual turnover.
CA Pramod Singhal treats GSTR-9 as a full-year compliance audit for every client, catching errors before they become a problem the portal flags first.
Fix: Treat the GSTR-9 filing cycle as a full-year audit of your GST compliance, not just another form. Use it as a structured opportunity to identify discrepancies, correct ITC reversals under Rules 42 and 43, and address any vendor mismatches. If your volumes are significant, this is not a process that should be handled without professional support.
Is Your GST House in Order?
GST compliance in 2026 is not forgiving of process gaps. The portal's AI-driven scrutiny means that errors which once took months to surface now generate notices within weeks. For a business that is scaling, this is not a back-office concern - it directly affects working capital, vendor relationships, and the ability to raise capital.
At CA Pramod Singhal, GST compliance is not a once-a-month task we complete before the deadline. It is a continuous, month-long process of reconciliation, verification, and structured review. Our team works with founders, CFOs, and finance managers to build compliance systems that prevent these mistakes from occurring - not just catch them after the fact.
If you would like a structured review of your current GST filing practices, schedule a consultation with our team. We are available Monday to Saturday, 10 AM - 7 PM, and respond to email enquiries within one working day.
Avoid costly GST mistakes with CA Pramod Singhal - reach out today for expert GST compliance support that protects your business.
FAQs
What is the most common GST compliance mistake businesses make in India?
The most common GST compliance mistake is a mismatch between GSTR-1 and GSTR-3B. When outward supply figures in both returns do not match, the GSTN portal flags the account automatically and issues demand notices without any manual intervention.
What happens if you claim ITC without reconciling GSTR-2B?
Claiming ITC without reconciling GSTR-2B means claiming credit the portal has not validated. If your supplier has not filed their GSTR-1, the credit does not appear in your GSTR-2B. Any credit claimed beyond this gets reversed with interest.
What is the late fee for not filing GSTR-3B on time?
The late fee for GSTR-3B is ₹50 per day for returns with tax liability. For nil returns, it is capped at ₹500. A pending GSTR-3B also blocks e-way bill generation, which can stall business operations entirely until the return is filed.
Which expenses are blocked from ITC claims under Section 17(5)?
Section 17(5) of the CGST Act blocks ITC on motor vehicles for personal use, construction of immovable property, food and beverages, beauty treatments, club memberships, and goods used for personal consumption — even when GST was paid on the purchase.
Who is liable to pay GST under the Reverse Charge Mechanism?
Under RCM, the recipient of goods or services pays GST directly to the government, not the supplier. It applies to legal services, GTA services, import of services, and commercial rent from unregistered landlords. Liability must be discharged in cash, not through ITC.
Is GSTR-9 mandatory for all businesses?
GSTR-9 is mandatory for businesses with an annual turnover above ₹2 crore. Businesses above ₹5 crore must also file GSTR-9C, the reconciliation statement. The filing deadline is December 31, and missing it attracts a late fee of ₹200 per day.