Six Input Tax Credit mistakes that trigger GSTR-3B notices

Input Tax Credit (ITC) is the working-capital backbone of any GST-registered business. It is also the most-scrutinised number on your GSTR-3B. The GSTN's auto-matching engine reconciles your claimed ITC against your suppliers' GSTR-1 every month, and mismatches trigger notices that take quarters to resolve.

Most ITC notices come from a small set of patterns. Fix the process and you stop the notices.

Mistake 1: claiming on GSTR-2A instead of GSTR-2B

Until 2021, you could claim ITC based on GSTR-2A — a dynamic, real-time view of what your suppliers had uploaded. Then came Rule 36(4) and Section 16(2)(aa): ITC is now restricted to invoices appearing in GSTR-2B, the static monthly statement generated on the 14th of the following month.

If you claim based on 2A and a supplier amends their GSTR-1 mid-month, your 3B and the GSTN view will diverge. The notice will say "ITC claimed but not reflected in 2B."

Fix: change your monthly close process. Wait for GSTR-2B (generated on the 14th) before locking 3B. Reconcile every invoice in 2B against your purchase register. Only claim what matches.

Mistake 2: ignoring blocked credits under Section 17(5)

Section 17(5) lists ITC that is permanently blocked, regardless of business use:

• Motor vehicles for seating up to 13 persons (with exceptions for transport-of-passengers business, driving schools, sale-of-vehicles business);
• Food and beverages, outdoor catering, beauty treatment, health services (unless used to make an outward taxable supply of the same category);
• Club, health, fitness centre memberships;
• Travel benefits to employees on vacation (LTC);
• Works contracts for construction of immovable property (except plant and machinery);
• Goods and services received for personal consumption;
• Goods lost, stolen, destroyed, written off, or given as gifts or free samples.

Common trap: claiming ITC on staff lunch invoices, gym memberships, or office construction. All blocked. Build a chart-of-accounts mapping: every expense category tagged as "ITC-eligible" or "blocked" at the time of voucher entry.

Mistake 3: not reversing ITC under Rule 42/43

If you make both taxable and exempt supplies, you must reverse a proportionate amount of common-input ITC. Rule 42 covers inputs and input services; Rule 43 covers capital goods (across 60 months).

Most businesses miss this because they think "we're only into taxable supplies." Then they earn interest on a savings account, or get rental income from a residential property — both exempt — and the proportionate reversal becomes due.

The formula isn't complex; the discipline of monthly application is. Build the Rule 42 calculation into your monthly close, even if the exempt turnover is currently zero.

Mistake 4: claiming ITC on RCM invoices before paying tax

Reverse Charge Mechanism (RCM) flips the GST liability — the recipient pays tax instead of the supplier. Common RCM scenarios: legal services from an advocate, GTA freight, import of services.

You can claim ITC on the RCM tax paid — but only after you have paid it. Claiming in the same month as accruing the liability, before the cash actually moves, breaks the matching. Worse, if you forget to pay RCM altogether, you owe both the tax and interest at 18%, plus you can't claim ITC.

Fix: have a separate RCM ledger. Every RCM accrual triggers a payment task. Only claim ITC after the bank confirmation.

Mistake 5: missing the November-of-next-FY deadline

ITC for an invoice must be claimed by the earlier of:

• 30 November of the financial year following the year of invoice; or
• The date of filing the annual return (GSTR-9).

A FY 2024-25 invoice you forgot must be claimed by 30 November 2025. After that, the ITC is lost — no way to claim, no carry-forward.

Reconcile your purchase register against your claimed ITC every quarter. Catch missed invoices early, before the deadline.

Mistake 6: claiming on supplier's cancelled or non-existent GSTIN

The GSTN flags ITC claimed against suppliers whose GSTIN is:

• Cancelled (effective date precedes invoice date);
• Suspended;
• Non-existent (validation fails).

This often happens with one-time vendors or small suppliers whose registration lapses. The ITC is denied; you also become a target for fake-invoice scrutiny.

Build a vendor onboarding check: validate GSTIN format, then verify active status on the GST portal, then re-verify quarterly for active suppliers. Block new transactions when a supplier's status changes.

A monthly close process that prevents notices

1. Day 1-10: Receive supplier invoices, post to purchase register, validate GSTINs. 2. Day 11-13: Reverse-charge tax payment for the month. 3. Day 14: Pull GSTR-2B. Reconcile against purchase register. Flag mismatches. 4. Day 15-18: Chase suppliers on mismatches. Get them to amend their GSTR-1. 5. Day 19: Apply Rule 42/43 reversals. 6. Day 20: File GSTR-3B with reconciled ITC.

Run this every month. The discipline pays for itself the first time you don't get a notice.