ITC has an expiry date. Your October pile decides whether you keep it.

₹86,400. That is the ITC sitting inside one ₹4.8 lakh fabrication invoice at 18%. Last October I watched a customer lose almost exactly that on a March bill their supplier never uploaded. The voucher was clean. The GSTIN checksummed. The arithmetic closed to the rupee. None of it mattered, because the credit had expired while the paper sat in a drawer.

I keep returning to that number because it makes the abstract concrete. Section 16(4) is not philosophy. It is a clock, and when it stops, no validator on earth restarts it.

This is not legal advice. Open the CGST Act on CBIC. If a blog (including this one) disagrees with the PDF in your browser, the PDF wins. Our section 16 post is the statutory map. This page is the clock.

₹86,400, gone in one missed date

Let me reconstruct the loss so you can check your own pile for the same shape. March 2026: machined components arrive, ₹4,80,000 plus 18% GST, ₹86,400 of ITC. Invoice enters Tally in April, posted to FY 2025-26 correctly. So far so good. Then nothing. The supplier, a small job shop, never filed that quarter's GSTR-1. No 2B line. Nobody noticed, because the voucher looked finished.

October comes. 2B recon flags the missing line. The customer calls the supplier, who promises to file. November 30 passes with the line still missing. ₹86,400 becomes a cost. Not a dispute, not a penalty. Just money that used to be theirs, converted into scrap value by a calendar.

Multiply that by every supplier who files late and you see why I write about clocks instead of checksums this month. One missed date costs more than a year of typos.

The earlier-of rule

Here is the part people skim, so I will go slowly. For FY 2025-26, invoices from April 2025 to March 2026, you must claim the credit by the earlier of 30 November 2026 and the day you file the annual return for 2025-26. Earlier of. Two dates walk in, the sooner one wins.

The sting most factories miss is the second date. File your annual return in October to close the books neatly, and you have just moved your own deadline forward a month. That is a decision, not an accident. I have seen it made accidentally more than once. Make it with your CA in the room.

And the mirror sting: an invoice that reaches you in December for March goods still belongs to the old year. The old year's clock, the old year's deadline. Late paper does not buy fresh time.

Four ordinary ways it happens

In my experience nobody loses ITC by misreading the Act. They lose it four ways, and I have now seen every one up close.

The silent supplier. Small job shop, files when reminded, and nobody reminded them since June. The ₹86,400 story above. Cure: a monthly 2B check with a chase list, started in July, not October.

The drawer. March photocopies found during Diwali cleaning, never entered, never reconcilable. Same-week entry discipline is the only cure and October entry is triage. See invoice date vs FY for the dating half of this mess.

The wrong year. March invoice dated into April books. Old-year credit never claimed, new-year books carry a stranger. Posting-date control at import catches it. See CSV import.

The eaten October. Three weeks spent fixing GSTIN typos and totals instead of chasing filings. By the time the pile is clean, the supplier has no filing window left. This is the one our gate exists to prevent: every bad document blocked at entry is an October hour spent on filings instead of typos. See the ITC checks.

The gate's part in this

Let me place our product honestly inside this story. The gate checks the document. Timing is not in the document. A voucher can pass checksum, HSN, arithmetic within ₹1, and regime, get AUTO_EXPORTED, post to Tally, and still lose its ITC to the clock. That is not a bug. It is the split between paperwork and the portal, and I would rather you hear it from me than from your CA in December.

What the gate buys is the only currency October accepts: weeks. Clean vouchers mean your 2B recon compares real lines instead of garbage from the first day. It will not tap you on the shoulder as 16(4) approaches. Posting date versus period close is your Tally discipline plus your CA. No software reads the calendar for you.

October, week by week

First week: pull 2B for the full year and diff it against the purchase register. Every missing supplier line is a chase, not a write-off yet. 1 vs 2B vs 3B is the map if your team is new to this.

Second week: chase supplier filings before your own entries. One filed GSTR-1 fixes ten vouchers at once. Call, then put it in writing with invoice numbers and amounts. Largest missing lines first.

Third week: enter every unentered scan for the old year. Drawer photocopies found after the deadline are scrap paper with GSTINs on them.

Fourth week: sit with the CA on the ambiguous ones. Debit notes, RCM, composition, job-work challans. Bring the scan and the 2B line. And freeze the annual return date deliberately, eyes open, CA in the room.