Content authored by practitioners with experience at Amazon India, Intuit QuickBooks, and the Tata Group. Meet the team →
Finance teams operating under pre-IMS assumptions treat GSTR-2B as a passive feed that auto-populates from supplier GSTR-1. Since October 2024, GSTR-2B is the output of an IMS decision pipeline. The structural shift changes who acts, when, what happens to mismatches, Rule 36(4) compliance burden, and the cash flow timing on ITC realisation — none of which are visible to teams that have not updated their workflow.
A side-by-side comparison maps the two models across six dimensions: who acts, when action happens, mismatch handling, Rule 36(4) evidence chain, cash flow timing, and audit trail composition. The IMS model is strictly the more rigorous of the two; the legacy model is functionally closed for current-period invoices.
Six-dimension comparison matrix, transition checklist for teams moving from legacy to IMS workflow, cash flow impact modelling for the deferred ITC scenarios, and Rule 36(4) audit-trail upgrade specification.
Operational gap analysis between current workflow and IMS-compliant workflow, cash flow impact projection per period, audit-trail upgrade plan, and implementation roadmap for transition to active in-cycle decision model.
Before October 2024, the monthly ITC workflow had three actors: the supplier, the GST portal, and the buyer. The supplier filed GSTR-1, the portal aggregated entries into GSTR-2B, and the buyer reconciled GSTR-2B against the purchase register to claim ITC in GSTR-3B. The buyer was passive throughout the upstream — the portal made decisions, the buyer accepted the output. Since October 2024, the buyer is the central decision-maker. Each inward invoice requires an explicit Accept, Reject, or Pending action before flowing into GSTR-2B. This is not a minor procedural update. It is a structural shift in how ITC reconciliation works.
The Two Models Side By Side
| Dimension | Traditional Model (Before Oct 2024) | IMS Model (Oct 2024 Onwards) |
|---|---|---|
| Who acts | Portal (auto-populates) | Buyer (explicit decisions) |
| When action happens | None — passive | 12th to 20th of each month |
| Source data | Supplier GSTR-1 | Supplier GSTR-1 + buyer IMS decisions |
| Mismatch handling | Discovered after GSTR-2B, resolved next month | Surfaced in IMS before GSTR-2B, resolvable in same cycle |
| Rule 36(4) evidence | Purchase register + GSTR-2B + GSTR-3B | Above + IMS Accept timestamp |
| Cash flow timing | Same-month ITC for filed invoices | Same-month ITC only for IMS-Accepted invoices |
| Audit trail artefacts | Three (invoice, GSTR-2B, GSTR-3B) | Four (above + IMS timestamp) |
| Control type | Corrective (after the fact) | Preventive (in cycle) |
| Decision authority | None — system-driven | Buyer-driven |
| ITC realisation latency | Day of GSTR-3B filing | Day of GSTR-3B filing for Accepted; one month later for Pending |
The shift is not partial. Every dimension changes.
Who Acts: Portal vs Buyer
In the traditional model, the buyer was a passive recipient. The portal generated GSTR-2B on the 14th by aggregating supplier GSTR-1 filings. The buyer downloaded the resulting document, reconciled it against the purchase register, and claimed ITC up to that amount.
In the IMS model, the buyer is the central decision-maker. The portal populates the IMS dashboard with supplier filings, but each invoice requires explicit buyer action. The portal does not pre-decide. GSTR-2B is generated as the output of buyer decisions, not as the input to buyer reconciliation.
The operational consequence: pre-IMS, a buyer with poor IMS hygiene still got a complete GSTR-2B (the portal made all decisions). Post-IMS, a buyer with poor IMS hygiene gets an incomplete GSTR-2B (Pending invoices are excluded) plus a tail of deemed-Accepted invoices the buyer never actively reviewed.
When Action Happens: Passive vs Nine-Day Window
The traditional model required no in-cycle action. The buyer’s only deadline was the 20th GSTR-3B filing date, by which time GSTR-2B had been generated and reconciled.
The IMS model requires action across a nine-day window from the 12th (IMS dashboard populated) to the 20th (GSTR-3B filing). Within this window:
- Day 12 to Day 14: review fresh IMS entries and post initial decisions before GSTR-2B generation.
- Day 14 to Day 20: post follow-up decisions on items that resolved in the latter half of the cycle.
For high-volume buyers, daily IMS pulls starting from Day 1 of the month spread the work across 20 working days. The 9-day window is the hard backstop, not the operating cadence.
Mismatch Handling: Corrective vs Preventive
Under the traditional model, a mismatch — say a supplier filing under the wrong GSTIN — surfaced after GSTR-2B was generated. The buyer’s options were: claim ITC anyway and risk DRC-01C notice, defer ITC and wait for supplier to file an amendment, or contest the entry in next month’s reconciliation. All options were corrective — fixing something that had already gone wrong.
Under the IMS model, the same mismatch surfaces in the IMS dashboard before GSTR-2B locks. The buyer can Reject the wrong-GSTIN entry preventively. The bad entry never reaches GSTR-2B. The supplier can correct via Type 9 amendment in the same cycle.
The IMS model is the more powerful control — it prevents bad ITC entries from reaching the GSTR-3B claim in the first place. The traditional model could only correct after the fact, with one-month delays and interest exposure.
Cash Flow Timing: Working Capital Impact
This is the dimension with the largest practical consequence for finance functions.
Under the traditional model, a buyer with ₹5 crore monthly inward purchases at 18 percent GST had ₹90 lakh of monthly ITC. The full ₹90 lakh was claimable in the same month’s GSTR-3B as long as suppliers filed GSTR-1 by the 11th. Cash flow timing was predictable: GST cash outflow was net of ITC, with the ITC available in-cycle.
Under the IMS model, the same ₹90 lakh ITC has three possible timings:
- Accepted before Day 20: Full ₹90 lakh ITC claimed in same-month GSTR-3B. Same as traditional.
- Pending past Day 20: Deferred to next month’s GSTR-2B (if Accepted before next cycle’s deadline). One-month working-capital lock on the deferred amount.
- Rejected: ITC permanently unavailable. Direct ITC loss equal to the rejected amount’s tax value.
For a buyer with a 10 percent Pending rate, that is ₹9 lakh of monthly working-capital lock — sustained over time if the Pending rate doesn’t reduce. A worked example for a ₹5 crore inward purchase company:
| Scenario | Pending Rate | Monthly ITC Deferred | Annual Cash Flow Impact |
|---|---|---|---|
| Best case (disciplined IMS) | 2% | ₹1.8 lakh | ₹21.6 lakh deferred ITC peak |
| Average case | 8% | ₹7.2 lakh | ₹86.4 lakh deferred ITC peak |
| Poor case (manual workflow) | 15% | ₹13.5 lakh | ₹1.62 crore deferred ITC peak |
The IMS model has redirected ITC realisation from a guaranteed in-cycle outcome to a workflow-dependent outcome. Teams with disciplined IMS workflows match traditional-model timing. Teams with poor workflows lock significant working capital.
Rule 36(4) Compliance: Three Artefacts vs Four
The traditional audit defence chain for an ITC claim had three artefacts: tax invoice, GSTR-2B presence, GSTR-3B Table 4 line. The auditor traced from purchase register entry to GSTR-2B presence to GSTR-3B claim.
The IMS audit defence chain has four artefacts: the three above plus the IMS Accept timestamp from the GST portal. The Accept timestamp evidences the buyer’s positive action on the invoice — the new evidentiary requirement under Rule 36(4) in the IMS-era interpretation.
Spreadsheet-based workflows rarely capture the IMS Accept timestamp. The timestamp is generated by the portal when the buyer clicks Accept; capturing it requires either manual logging at the moment of action (error-prone) or automated capture via a reconciliation tool that posts the Accept on the buyer’s behalf and records the timestamp.
For the broader Rule 36(4) and Section 16 audit defence framework, see IMS vs GSTR-2B reconciliation.
Decision Authority Distribution
Traditional model: no decision authority needed beyond the GSTR-3B filer (typically a finance manager or controller). The system made all upstream decisions.
IMS model: decision authority is distributed across the AP team (analyst, manager, controller). A role-based authority split prevents single-actor risk:
- AP analyst: Accept on auto-recommended matches.
- AP manager: Reject and review escalated Pending.
- Controller: Override authority on disputed items.
The audit trail captures actor identity per decision, supporting internal-control requirements under ICFR for listed entities.
Transitioning Workflows From Traditional to IMS
Teams that have not updated their workflow since October 2024 typically exhibit three symptoms:
- Rising Pending count — invoices accumulate in IMS without action because the team is operating the old reconciliation cadence (after-the-fact rather than in-cycle).
- Unexplained ITC discrepancies in GSTR-3B Table 4 — claimed ITC exceeds GSTR-2B ITC because the team is reading from the purchase register rather than the post-decision GSTR-2B.
- DRC-01C notices — the portal flags the discrepancy between claimed ITC and IMS-decided GSTR-2B.
The transition checklist:
- Set up daily or twice-monthly IMS dashboard pull.
- Implement purchase-register-to-IMS match logic with action recommendations.
- Establish role-based authority split (analyst, manager, controller).
- Add 30-day Pending aging tracker with day-25 alerts.
- Capture IMS Accept timestamps in the audit trail.
- Reconcile GSTR-3B Table 4 against post-decision GSTR-2B, not purchase register.
Each step is mechanical. The total transition for a mid-market team takes 4 to 6 weeks if done with a purpose-built tool. Manual transition on spreadsheets is possible but typically does not survive a quarter — the Pending queue grows beyond manageable size.
A purpose-built GST reconciliation software handles the six steps as a native workflow. For multi-process integration with TDS, NACH, and bank reconciliation, a unified reconciliation software India maintains the audit trail across processes that share supplier master data.
For the foundational mechanics, see GSTR-2A versus GSTR-2B for the upstream context and the GSTR-2B reconciliation guide for the downstream reconciliation against GSTR-3B. The authoritative portal specification for IMS lives on the GST portal under the GSTR-2B services menu.