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Buyer loses ITC when supplier hasn't been paid within 180 days (Rule 37) or hasn't filed GSTR-3B by September 30 (Rule 37A). 18% interest applies on utilized ITC.
Monitor payment aging per supplier invoice for Rule 37 (180-day trigger) and supplier GSTR-3B filing status for Rule 37A (September 30 trigger). Re-availment tracked separately — not subject to Section 16(4) time bar.
Rule 37: 180-day window from invoice date, proportionate reversal, 18% interest under Section 50. Rule 37A: reversal by November 30, re-availment when supplier files.
Automated reversal alerts at 150-day mark, GSTR-3B reversal entries, re-availment tracker when payment made or supplier files, and interest liability calculation.
Rule 37 and Rule 37A ITC reversal provisions create two independent tracking obligations for every invoice in the purchase register. Finance teams at enterprises with 500 or more vendor invoices per month must monitor both the 180-day payment clock and the supplier filing status simultaneously. Missing either trigger results in interest liability under Section 50, and the reconciliation complexity scales linearly with vendor count.
What Rule 37 Requires: The 180-Day Payment Reversal
Rule 37 of the CGST Rules mandates that if the buyer has not paid the supplier the full invoice value (including GST) within 180 days of the invoice date, the ITC claimed on that invoice must be reversed proportionately. The reversal must happen in the GSTR-3B for the period immediately following the 180-day expiry.
A worked example: an invoice dated January 10, 2024 for ₹11,80,000 (₹10,00,000 + ₹1,80,000 GST at 18%) has a 180-day expiry on July 8, 2024. If the buyer has paid ₹7,08,000 (60% of the invoice) by July 8 and ₹4,72,000 remains unpaid, the ITC to be reversed is ₹72,000 (40% of ₹1,80,000 GST). This reversal must appear in the July 2024 GSTR-3B, due August 20, 2024.
Interest under Section 50 at 18% per annum applies from the date of utilisation of the ITC until the date of reversal, but only if the credit was actually utilised to offset tax liability. Credit that was availed but sitting unused in the electronic credit ledger does not attract interest on reversal.
What Rule 37A Requires: The Supplier Non-Filing Reversal
Rule 37A, introduced by CGST Notification 26/2022 effective January 1, 2023, addresses a different default. If the supplier has not filed their GSTR-3B by September 30 of the financial year following the year in which the ITC was availed, the buyer must reverse the ITC in the GSTR-3B filed on or before November 30 of that year.
The supplier’s filing status is verifiable through GSTR-2B. If an invoice appeared in GSTR-2B because the supplier filed GSTR-1 but subsequently did not file GSTR-3B, the buyer must still reverse.
Rule 37 vs Rule 37A vs Rule 42/43 Reference Table
| Provision | Trigger | Reversal Deadline | Interest Applicable | Re-availment Permitted | Time Limit on Re-claim |
|---|---|---|---|---|---|
| Rule 37 | Buyer non-payment within 180 days | GSTR-3B for period after 180-day expiry | 18% p.a. if ITC was utilised | Yes, upon payment | No time limit |
| Rule 37A | Supplier non-filing of GSTR-3B | By November 30 of following FY | 18% p.a. if ITC was utilised | Yes, upon supplier filing | No time limit |
| Rule 42/43 | Common credit on exempt supplies | Monthly/annual apportionment | Not applicable (apportionment, not default) | Adjusted annually | Within same FY |
| Section 16(4) | Time bar on initial ITC claim | November 30 of following FY | Not applicable | No recovery possible | Permanent |
The Critical Distinction: Re-availment Has No Time Bar
Both Rule 37 and Rule 37A permit re-availment of reversed ITC once the underlying default is cured. For Rule 37, this means payment to the supplier. For Rule 37A, this means the supplier files the pending GSTR-3B. The re-availment is not subject to the Section 16(4) time limit. This distinction is operationally significant: an enterprise that reversed ₹15 lakh in ITC under Rule 37A in November 2024 because a supplier had not filed GSTR-3B can re-avail the full amount in April 2026 when the supplier eventually files, with no penalty and no additional tax.
DRC-01C and the Aggregate Mismatch Problem
DRC-01C auto-notices, introduced in 2024, trigger when a buyer’s ITC in GSTR-3B exceeds the GSTR-2B amount for any period. The buyer has 7 days to respond, either accepting the difference and paying the tax with interest, or providing an explanation. Rule 37A reversals that have not been reflected in GSTR-3B will compound the DRC-01C mismatch, creating a cascading compliance burden.
GST reconciliation software that tracks both payment ageing (for Rule 37) and supplier filing status (for Rule 37A) against each invoice converts these compliance obligations from quarterly fire drills into automated exception workflows. The system flags invoices approaching the 180-day mark 30 days in advance and monitors GSTR-2B for supplier filing gaps weekly.
For enterprises operating across multiple GSTINs, reconciliation software India-wide deployments consolidate Rule 37 and Rule 37A exposure across all registrations, preventing the common failure mode where one GSTIN reverses correctly while another misses the deadline entirely.
Supplier filing status, GSTR-2B data, and the ITC reversal filing interface are available on the GST portal.