Mismatched 2B, blocked credits under 17(5), late reconciliation — the costly ITC errors we see most often and how to stop them this quarter.
Input Tax Credit is the single biggest lever in your GST margin. Most businesses lose 3–8% of their eligible ITC every year — not to fraud, but to small, fixable mistakes. Over a ₹5 Cr business, that's ₹15–40 lakh quietly walking out the door. Here are the five mistakes we see most often, and the workflow that plugs each one. Monthly 2B reconciliation is part of our GST return filing service.
Since Section 16(2)(aa) was inserted, ITC is only allowed if the invoice appears in your GSTR-2B. Claiming on the basis of a supplier-issued invoice that hasn't been filed yet is the single fastest way to attract an ASMT-10 mismatch notice. The fix is non-negotiable: reconcile every month between the 14th (when 2B drops) and the 20th (when 3B is due).
Section 17(5) is a long list of expenses where ITC is permanently blocked, no matter how legitimately incurred:
Claiming blocked ITC and reversing it later still attracts 24% p.a. interest under Section 50(3) — not 18%. Auditors zoom in on this.
ITC for a financial year must be claimed by the earlier of: 30th November of the next financial year, or the date of filing the annual return GSTR-9. Miss the window and the credit is permanently lost. We routinely see late-arriving supplier invoices (especially from MSME vendors) that businesses simply forget to chase past March.
Run a quarterly 'ITC chase list' — every supplier whose invoice you booked but who hasn't reflected it in their GSTR-1. Email a polite reminder. Most fix it within a week to keep your business.
Three trigger events demand ITC reversal that businesses regularly miss:
If you have both taxable and exempt supplies, common-use ITC (rent, audit fees, marketing) must be apportioned under Rule 42 / 43. Most growing businesses with a mix of GST-charged services and exempt activities (e.g., healthcare + retail) silently over-claim every month. A quarterly Rule 42 computation kept on file is the audit-proof fix.
| Tool | Use it for |
|---|---|
| Tally / Zoho Books / Custom ERP | Source of truth for purchase register |
| ClearTax / IRIS / Avalara | Automated 2B vs books reconciliation |
| Excel pivot tables | Quick monthly variance dashboard |
| GST portal | Final ground truth — always cross-check |
If you've received an ASMT-10, DRC-01A or DRC-01, don't panic. The standard response sequence:
Pick one month. Run a full ITC reconciliation, identify your top ten missing suppliers, chase them in writing, build a Rule 42 working if applicable, and document everything in a single PDF you can hand to any auditor. Repeat for two more cycles. By month four, ITC leakage is no longer the question — margin is.
Senior contributor at Taxpex Consultancy. Reviewed by a practising Chartered Accountant. Published on 22 January 2026 · Updated on 22 January 2026.
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