Most input tax credit (ITC) is not lost because of a complicated legal position. It is lost because an invoice never reached the books, or a supplier never reported it, and nobody compared the two in time.
Since the law now allows ITC only on invoices that appear in your GSTR-2B (Section 16(2)(aa) of the CGST Act, read with Rule 36(4)), reconciling your purchase register against GSTR-2B is no longer a year-end clean-up job. It is a monthly control. This article sets out the checklist we follow every month, a worked example with real numbers, and the mistakes that cost small businesses the most.
Why GSTR-2B decides your ITC
GSTR-2B is a static monthly statement of the inward supplies your suppliers have reported in their GSTR-1 or IFF. It is generated on the 14th of the following month. If an invoice is not in your GSTR-2B, you cannot claim credit for it in that month's GSTR-3B, however genuine the purchase.
Three other rules make timing important:
- Invoice Management System (IMS): every supplier invoice now appears in IMS, where you can accept, reject or keep it pending. Records you do not act on are treated as accepted when GSTR-2B is generated. Rejecting a wrong invoice before the 14th keeps it out of your credit.
- The time limit under Section 16(4): ITC for a financial year must be claimed by 30 November of the following year (or the date you file the annual return, if earlier). An invoice you discover in December is usually lost.
- The 180-day payment rule (Rule 37): if you do not pay a supplier within 180 days of the invoice date, the credit already taken must be reversed with interest.
The GST portal is also steadily moving GSTR-3B towards auto-populated, locked figures. The practical conclusion is simple: your books must agree with GSTR-2B and IMS before you file, not after.
The monthly calendar
For a monthly filer, the month runs like this:
| Date | What happens | Your action |
|---|---|---|
| 1st–5th | Previous month closes | Finish entering every purchase bill; freeze the purchase register |
| By the 11th | Suppliers file GSTR-1 | Remind key suppliers who file late |
| 11th–13th | Invoices appear in IMS | Review IMS: accept, reject wrong invoices, keep genuinely doubtful ones pending |
| 14th | GSTR-2B is generated | Download GSTR-2B and run the reconciliation |
| 15th–18th | Exceptions are handled | Chase suppliers, correct your own entries |
| By the 20th | GSTR-3B is due | Claim only what the reconciliation supports |
Quarterly (QRMP) filers follow the same sequence, just on a quarterly cycle.
The checklist
Print this and tick it off every month.
Before you reconcile
- Every purchase bill for the month is entered, including bills sitting with the owner or in the delivery van
- Purchase entries for the month are locked, so figures do not move while you reconcile
- Supplier GSTINs in your ledger have been checked against the GST portal
- IMS has been reviewed and wrong or duplicate invoices rejected before the 14th
- GSTR-2B for the month has been downloaded (Excel or JSON)
While you reconcile
- Match on supplier GSTIN + invoice number + invoice date, not on supplier name
- Normalise invoice numbers before matching (remove spaces, "INV/", leading zeros)
- Put every line into one of the three buckets below
- Check tax values, not just taxable values: a wrong IGST/CGST split is a mismatch
- Flag credit notes separately and confirm they have been reduced from ITC
After you reconcile
- Send one consolidated email or WhatsApp to each supplier with their missing invoices
- Correct your own data-entry errors the same week
- Record which items are carried forward to next month, with the amount
- Check supplier payments against the 180-day rule
- Save the reconciliation file with the GSTR-3B working for that month
The three buckets
Anything that does not match cleanly belongs in one of three buckets. Each has a different owner and a different fix.
| Bucket | What it usually means | What to do |
|---|---|---|
| In books, not in GSTR-2B | Supplier has not filed, filed under the wrong GSTIN, or filed late | Do not claim this month. Ask the supplier to report it; claim once it appears |
| In GSTR-2B, not in books | A bill that never reached accounts, or an invoice that is not yours | Find the bill and book it, or reject it in IMS if it is not yours |
| Matched with a value difference | Typing error, rate difference, or a revised invoice | Check the physical bill. Correct your entry, or ask the supplier to amend |
A worked example
A Coimbatore trading business records 48 purchase invoices in June, with total GST of ₹2,23,200. GSTR-2B for June shows 45 invoices. Here is what the reconciliation finds:
| Result | Invoices | GST in books (₹) | GST in GSTR-2B (₹) |
|---|---|---|---|
| Fully matched | 41 | 1,87,200 | 1,87,200 |
| Value difference | 3 | 14,400 | 12,600 |
| In books, not in GSTR-2B | 4 | 21,600 | — |
| In GSTR-2B, not in books | 1 | — | 3,600 |
| Total | 2,23,200 | 2,03,400 |
What the business does:
- Matched (₹1,87,200): claimed in full.
- Value difference (₹1,800 gap): two of the three bills were entered with a wrong amount in the books. The third was a supplier error. The business claims the ₹12,600 that GSTR-2B supports and asks the supplier to amend the third invoice.
- Missing from GSTR-2B (₹21,600): three invoices are from one supplier who filed GSTR-1 late. The fourth was reported under an old GSTIN. All four are held back and followed up.
- Missing from books (₹3,600): a bill was found in the owner's car. It is booked and claimed.
ITC claimed this month is ₹2,03,400. The ₹23,400 at risk is not written off. It goes onto a follow-up list with a supplier name and an owner. Done every month, most of it comes back within one or two cycles. Left for six months, most of it never does.
Common mistakes
- Reconciling a moving target. If bills are still being entered while you reconcile, the exception list never ends. Freeze first.
- Matching on names. "Sri Murugan Traders", "Sri Murugan Trdrs" and "SMT" are the same supplier. The GSTIN never changes.
- Ignoring IMS. An invoice left unattended is treated as accepted, including a wrong one.
- Chasing suppliers one invoice at a time. One consolidated list per supplier gets a faster response than twenty separate calls.
- Treating reconciliation as annual. A missing invoice raised in the current month is usually recoverable. The same invoice raised after the Section 16(4) deadline rarely is.
Where a tool helps
The checklist above works with Excel. The slow part is the matching: normalising invoice numbers, catching near-matches and preparing supplier-wise follow-up lists. That is the part we automated in TRecon, which reconciles your purchase register with GSTR-2B and produces the three buckets and the follow-up lists in minutes.
This article is general guidance, not legal advice. Check the current GST notifications or speak to your tax consultant for your specific case.
