A practical guide for SME owners and finance teams — clean up your books, protect your ITC, and close Q2 without surprises before 30 September 2026.
Q2 of FY 2026-27 (July to September 2026) closes on 30 September. For most SMEs, that date pass quietly — GST returns get filed, books get updated, and the quarter ends without anyone stopping to check whether the two actually match each other.
That mismatch, left unresolved, compounds. ITC that is in your books but missing from GSTR-2B quietly disappears after October 2026 — the last date to claim FY 2025-26 ITC. Supplier invoices with wrong GSTINs go unresolved, permanently blocking credits. Output tax discrepancies between GSTR-1 and your sales register go unnoticed until a GST department notice arrives.
This guide gives you a practical Q2 reconciliation framework — what to check, why it matters, what the new hard-locking rules changed, and exactly how to close the quarter cleanly before 30 September.
What GST-Books Reconciliation Actually Means
Reconciliation is the process of ensuring that what your books show matches what the GST portal shows — for both your sales (output) and your purchases (input tax credit). When these two match, your GST returns are defensible, your ITC is maximized, and your GSTR-9 annual return at year-end becomes straightforward.
When they do not match, the gaps fall into one of three categories:
- Timing differences: Invoices booked in one month, filed in another. Manageable if tracked.
- Supplier errors: Wrong GSTIN, wrong invoice amount, or non-filing. Require vendor follow-up and have a deadline.
- Internal errors: Wrong tax rate applied, ineligible ITC claimed, reverse charge missed. Require correction before year-end.
The Q2 quarter-end is the right moment to catch all three — with enough time left to resolve most supplier issues before the FY 2025-26 ITC lapse deadline in October 2026.
What Changed: The Hard-Locking of GSTR-3B and What It Means for Your Books
From July 2025 onwards, the GST portal implemented a fundamental change in how GSTR-3B works. It is the most significant shift in GST compliance workflow since ITC reconciliation rules were tightened in 2022 — and many SMEs are still not adjusting their processes accordingly.
Phase 1 (July 2025 — now active): Output Liability Locked
Tables 3.1 and 3.2 of GSTR-3B — which report your outward (sales) tax liability — are now non-editable. They are auto-populated from your GSTR-1/IFF filing and locked. You cannot override them.
What this means in practice: If you made an error in GSTR-1 — wrong invoice value, wrong tax rate, missing invoice — you cannot fix it directly in GSTR-3B anymore. The only correction window is GSTR-1A, which must be filed before GSTR-3B for the same period. GSTR-1A can only be filed once per period, so it must be accurate.
IMPORTANT WARNING
The GSTR-1A window closes permanently once GSTR-3B is filed.
If you discover an error in GSTR-1 after filing GSTR-3B for the same period, your only option is an amendment in the next month’s GSTR-1 — which flows into GSTR-3B in that future period, not retroactively. For significant errors, this can mean overpaying tax for a month with no immediate correction. The lesson: GSTR-1 must be filed accurately, and verified before GSTR-3B is submitted.
Phase 2 (July 2026 — targeted): ITC Locking
The Finance Ministry and GSTN have indicated that Table 4 of GSTR-3B — ITC claims — will also be hard-locked in Phase 2, drawing data exclusively from GSTR-2B. Once implemented, you will not be able to manually enter or adjust ITC figures in GSTR-3B. Only what appears in GSTR-2B can be claimed.
What this means for Q2 preparation: If Phase 2 arrives mid-quarter, any ITC mismatch between your purchase register and GSTR-2B that you have not resolved will simply become unclaimed credit — permanently. The time to resolve those mismatches is now, not when the portal blocks you.
CPC INSIGHT
Many SMEs operating in Delhi NCR and Faridabad discovered Phase 1 hard-locking only when the portal returned an error on submission — after GSTR-1 had already been filed with a mistake. CPC Services now runs GSTR-1 verification for clients before submission as a standard step, precisely because the GSTR-1A correction window is too narrow to rely on as a safety net.
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The Q2 Urgency: FY 2025-26 ITC Lapses After October 2026
This is the deadline that makes Q2 reconciliation time-sensitive rather than merely good practice.
Under Section 16(4) of the CGST Act, Input Tax Credit for FY 2025-26 can only be claimed until the earlier of:
- The due date of the September 2026 GSTR-3B return (i.e. 20 October 2026 for monthly filers), or
- The date of filing the GSTR-9 annual return for FY 2025-26
After that date, unclaimed ITC for FY 2025-26 lapses permanently. It cannot be carried forward. It cannot be reclaimed.
KEY TAKEAWAY
Any purchase invoice from FY 2025-26 that has not yet appeared in your GSTR-2B — because the supplier has not filed their GSTR-1, or because a GSTIN mismatch blocked it — must be resolved before your September 2026 GSTR-3B is filed. After that, the credit is gone.
This means Q2 (August–September 2026) is your last window to chase suppliers, fix GSTIN errors, and claim all eligible ITC from the past financial year. Use it.
What to Reconcile: The Four-Point Q2 Checklist
A thorough Q2 reconciliation covers four distinct areas. Work through them in this order — each one builds on the previous.
1. Reconcile Sales Register vs GSTR-1 (Output Reconciliation)
Match your internal sales register or Tally/ERP export against what was filed in GSTR-1 for July and August 2026 (and any outstanding months from Q1).
What to check:
- Total taxable turnover: Does the sum of invoices in your books match the taxable value in GSTR-1 Tables 4 and 5?
- Tax rate application: Were the correct GST rates applied — 5%, 12%, 18%, 28% — to each category of goods or services?
- Credit notes: Is every credit note issued in your books reported in GSTR-1? Missing credit notes mean overstated tax liability.
- B2B vs B2C classification: Were all invoices issued to GST-registered buyers correctly reported as B2B (with GSTIN)? B2C invoices with wrong classification block the buyer’s ITC.
- Advance receipts: Did you receive any advances in Q2 for which supply is pending? These must be reported in GSTR-1 under Table 11.
With hard-locking in effect: Any error found in July or August GSTR-1 that has not yet been corrected via GSTR-1A must be carried as an amendment into the September GSTR-1 (Table 9A). Do not wait — amendments are time-bound and affect the buyer’s ITC in the period they are made.
2. Reconcile Purchase Register vs GSTR-2B (ITC Reconciliation)
This is the most critical — and most time-consuming — reconciliation step. GSTR-2B is the fixed, auto-generated ITC statement on the portal, available after the 14th of each month. Your purchase register is what your books show you paid in GST to vendors.
The matching exercise:
Download GSTR-2B for July 2026 (available from 14 August) and August 2026 (available from 14 September). Export your purchase register for the same period from Tally/Busy/Zoho. Match each invoice using GSTIN + Invoice Number as the primary key.
Every invoice falls into one of five buckets:
| Bucket | Situation | Action Required |
| A — Match | Invoice in books AND in GSTR-2B, amounts agree | Claim ITC. No action needed. |
| B — Amount diff | Invoice in both, but amounts differ | Verify original invoice. If supplier error, request GSTR-1 amendment. If your books are wrong, correct the entry. |
| C — In books, not 2B | Supplier(s) has not filed GSTR-1, or filed with wrong GSTIN | Chase suppliers immediately. FY 2025-26 invoices must appear in September 2026 GSTR-2B or ITC lapses. |
| D — In 2B, not books | Supplier filed an invoice you have not recorded | Verify from the original document. Account for the purchases if legitimate and eligible for ITC. If wrongly uploaded by a supplier, reject in IMS. In case some personal purchases not relating to business has been uploaded, ignore it.ours. |
| E — Ineligible | Invoice in GSTR-2B but ITC not claimable (Section 17(5)) | Do NOT claim ITC. Reverse in Table 4(B) of GSTR-3B. Examples: motor vehicles, food, personal use items. |
IMS action reminder
If you have not acted on invoices in the Invoice Management System (IMS) before GSTR-2B was generated on the 14th, those invoices were auto-accepted. Review the IMS dashboard now — especially for credit notes and high-value invoices — and use the Recompute GSTR-2B function if you take action after the 14th.
3. Check ITC Reversal Obligations
Not all ITC that appears in GSTR-2B can be claimed. Certain rules require you to reverse ITC even when the supplier has correctly filed. Q2 is the time to verify all reversal obligations are correctly applied.
Key reversal rules to check:
- Rule 37 — 180-day payment rule: If you claimed ITC on an invoice but have not paid the supplier within 180 days of the invoice date, that ITC must be reversed. Once you pay the supplier, you can re-avail the credit. Check all invoices from Q4 FY 2025-26 (January–March 2026) — the 180-day window for those invoices closes in Q2 2026.
- Rule 37A — Supplier GSTR-3B non-filing: If your supplier filed GSTR-1 (so the invoice appears in your GSTR-2B) but has not filed their GSTR-3B by 30 September 2026, you must reverse the ITC in your November 2026 GSTR-3B. Monitor supplier filing status — not just GSTR-1, but GSTR-3B.
- Rule 42/43 — Mixed use: If your business has both taxable and exempt supplies, ITC on common inputs must be reversed proportionately. Calculate and apply this reversal monthly — do not let it accumulate.
- Section 17(5) — Blocked credits: Motor vehicles (in most cases), food and beverages, club memberships, health services, construction materials for own building, personal use items — ITC on these is always blocked, even if the invoice is in GSTR-2B. Ensure these are excluded from your Table 4(A) claim and included in Table 4(B) reversals.
REMINDER
Reverse charge mechanism (RCM): Table 3.1(d) of GSTR-3B — inward supplies liable to RCM — is NOT auto-populated from GSTR-2B. It must be manually entered every month. If your business pays for import of services, purchases from unregistered vendors (in notified categories), or uses goods transport agencies, verify this table is filled correctly for each month of Q2.
4. Reconcile Books Revenue vs GST Turnover
The final reconciliation step connects your profit and loss account to your GST returns — the check that auditors, lenders, and the GST department run automatically.
What to compare:
- Revenue in P&L vs Total taxable turnover in GSTR-1 filings: These will almost never match exactly — but you should be able to explain every difference.
Common legitimate differences:
- GST is not revenue — your P&L shows net revenue (excluding GST collected), but if you accidentally booked GST as income, it inflates revenue
- Exempt supplies — sales that are GST-exempt (certain agricultural produce, healthcare, education) appear in books but not in taxable GST turnover
- Advances — GST may have been paid on advances received before supply, which appear in GST returns but not yet in revenue (because revenue recognition follows supply)
- Branch transfers — inter-GSTIN stock transfers between your own branches are taxable under GST but not revenue in consolidated accounts
What is not acceptable: A large, unexplained gap between P&L revenue and GST turnover. This is exactly what the GST department’s automated scrutiny system looks for — and it is the most common trigger for a GST audit for SMEs. Document every difference with a line-by-line reconciliation note.
CPC INSIGHT
CPC Services prepares a formal revenue-GST reconciliation statement for every client at quarter-end. When a GST department inquiry arrives — or when the business applies for a bank loan and the bank requests financials — this document is already ready. It takes two hours to prepare proactively; it takes two weeks to reconstruct under pressure.
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Your Q2 Reconciliation Action Plan: August to September 2026
Here is a sequenced plan for closing Q2 cleanly. Work through this in August — do not leave it to the final week of September.
| When | Action | Why It Cannot Wait |
| 14–20 Aug | Download July GSTR-2B. Begin purchase register vs GSTR-2B match for July. | GSTR-2B is only available from 14th. Start immediately — supplier follow-ups take 2–3 weeks. |
| 20 Aug | File July GSTR-3B with reconciled ITC. Flag all Bucket C invoices for supplier chase. | Any ITC claimed without GSTR-2B backing is exposed to 18% interest notice. |
| 20–31 Aug | Chase all FY 2025-26 Bucket C suppliers. Send written requests to file/amend GSTR-1. | Suppliers need time to file. September GSTR-2B (14 Sep) is the last chance for FY 2025-26 ITC. |
| 1–11 Sep | Verify GSTR-1 for August is accurate before filing. Correct via GSTR-1A if needed, before GSTR-3B. | Hard-locking means GSTR-1A is the only correction window. It closes when GSTR-3B is filed. |
| 11 Sep | File August GSTR-1. Verify all outward invoices, credit notes, advances are accurately reflected. | GSTR-2B for your buyers is generated based on your August GSTR-1. Errors block their ITC. |
| 14 Sep | Download August GSTR-2B. Begin purchase register match for August. Check FY 2025-26 Bucket C invoices. | This is the final GSTR-2B in which FY 2025-26 ITC can appear. Any missing invoice must be chased now. |
| 14–18 Sep | Run full Q2 revenue vs GST turnover reconciliation. Document all differences. | Needed for GSTR-9 later in year and as a clean audit trail if GST department queries arise. |
| 18–19 Sep | Verify all Rule 37 reversal obligations. Check 180-day payment status on Q4 FY 25-26 invoices. | The 180-day clock on January–March 2026 invoices expires in this window. |
| 20 Sep | File September GSTR-3B with all FY 2025-26 ITC claimed. This is the last return for claiming FY25-26 ITC. | After the October 20 deadline, any unclaimed FY 2025-26 ITC lapses permanently. |
How to Chase Non-Filing Suppliers — Without Damaging the Relationship
Supplier non-filing is the most common cause of Bucket C mismatches. The ITC you paid in GST is sitting unclaimed in your books, and it will lapse if the supplier does not file before September 2026 GSTR-2B is generated.
Practical approach:
- Identify the backlog first: Export a vendor-wise summary of Bucket C invoices from your reconciliation. Know which supplier owes you what amount before making contact — having the invoice number and GST amount makes the conversation precise.
- Communicate in writing: Send an email or WhatsApp message with the specific invoice numbers and dates that are missing from GSTR-2B. Ask them to file or amend their GSTR-1 before 10 September 2026 so it appears in your September GSTR-2B.
- Make it easy for them: Many small vendors do not file their own GST returns — their accountant does. Provide the invoice details clearly so the accountant can identify and correct the specific entry quickly.
- For high-value repeat offenders: If a supplier consistently fails to file GSTR-1 on time — blocking your ITC every quarter — factor this into your vendor selection process. Repeated ITC blockage from the same supplier is a direct, quantifiable business cost.
QUICK TIP
A supplier who has not filed their GSTR-3B by 30 September 2026 triggers a Rule 37A reversal for you — even if they correctly filed GSTR-1. You must reverse the ITC in November 2026 GSTR-3B and can only reclaim it once they file. This is why monitoring supplier GSTR-3B compliance alongside GSTR-1 matters in Q2.
5 Reconciliation Mistakes SMEs Make Every Quarter
These are the errors CPC Services corrects most frequently for SME clients who do their own GST filing.
1. Using GSTR-2A instead of GSTR-2B for ITC claims
GSTR-2A is dynamic and keeps updating — it is useful for monitoring during the month. GSTR-2B is static and fixed on the 14th — it is the legal basis for ITC claims. Many businesses download GSTR-2A and use it for reconciliation, then find their ITC claims don’t match what the portal processes during GSTR-3B submission. Always use GSTR-2B as your final reference for filing.
2. Reconciling annually instead of monthly
Quarterly or annual reconciliation means 3–12 months of mismatches to resolve at once — with suppliers who may have closed, changed GSTINs, or simply lost the original records. Monthly reconciliation means a manageable list of 5–10 open items per cycle, resolved before the next filing. The September ITC lapse deadline makes annual reconciliation particularly dangerous.
3. Claiming ITC on ineligible expenses
Section 17(5) blocks ITC on a specific list of expenses — motor vehicles used for personal transport, restaurant meals, club memberships, health insurance (in certain cases), construction of own building, and goods or services for personal use. These invoices appear in GSTR-2B but the ITC cannot be claimed. Claiming them is one of the most common GST notice triggers — the department’s automated system flags ITC claimed that includes Section 17(5) items.
4. Not checking the IMS dashboard before filing GSTR-3B
Inaction in the Invoice Management System is treated as acceptance. If a supplier filed an incorrect invoice — wrong amount, wrong GSTIN, or a transaction that never happened — and you did not explicitly reject it in IMS before GSTR-2B was generated, it flows into your GSTR-2B as accepted ITC. Check the IMS dashboard after every GSTR-2B generation, specifically the ‘Rejected Records’ tab for credit notes.
5. Filing GSTR-3B before GSTR-1A when a correction is needed
Since hard-locking in July 2025, GSTR-1A is the only mechanism to correct outward supply data in the same period. Once GSTR-3B is filed, GSTR-1A for that period closes permanently. Many businesses — particularly those filing close to the due date — submit GSTR-3B without realizing a GSTR-1 error needs correction via GSTR-1A first. The sequence must be: Verify GSTR-1 → File GSTR-1A if correction needed → Then file GSTR-3B.
ADVISORY
If you have never done a formal GST-books reconciliation: Start with the current month’s GSTR-2B and your July purchase register. The first reconciliation always takes longer — typically a full working day for a business with 50–100 monthly purchase invoices. Once the system is in place, monthly reconciliation takes 2–3 hours. The time investment in August saves the investigation time in October when notices arrive.
Does CPC Services handle GST reconciliation for SMEs?
Yes. CPC Services manages complete GST reconciliation for SME clients across Faridabad and Delhi NCR — including monthly GSTR-2B vs purchase register matching, supplier follow-ups for Bucket C invoices, ITC reversal calculations, GSTR-1A corrections, and quarter-end revenue vs GST turnover reconciliation. Since 1987, we have handled GST compliance as an integrated part of accounting — not as a separate exercise.
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Related Reading
→ July 2026 GST & TDS Due Dates: Don’t Miss These Compliance Deadlines
→ 10 Signs Your Growing Business Needs a Virtual CFO Right Now
→ The Simple SME Accounting Checklist for a Better 2026
Don’t Let Mismatches Become Notices.
CPC Services handles GST reconciliation, ITC matching, and quarterly book closure for SMEs across Faridabad and Delhi NCR. Your September deadline is closer than you think.
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