Anomaly check
Rate mismatch, keyed to the date of supply
The slab structure changed with effect from 22 September 2025. A financial year now spans two regimes, so a rate that was correct in June can be wrong in November.
Sec. 9 r/w Sec. 15, CGST Act 2017 and the rate notifications in force
Law current as of 21 September 2026
Why a fixed slab table is now wrong
- Any check that compares a charged rate against one fixed list of slabs will either flag correct invoices or pass incorrect ones, depending on which side of 22 September 2025 the supply falls.
- The two-rate structure of 5% and 18%, with a 40% rate on select goods, applies from that date. Supplies before it are tested against the earlier slabs, which included 12% and 28%.
- A rate check therefore has to read the invoice date first and only then decide what a valid rate is. Our engine does exactly that, and every finding carries the date the statutory position was reviewed.
What a rate error actually costs
- Charge too little and the shortfall is recoverable from the client with interest, often after the client has already been paid by their customer.
- Charge too much and the recipient's credit is questioned, and the excess has to be refunded or a credit note issued.
- Either way the classification, not the arithmetic, is what has to be defended.
How to correct it
- Confirm the HSN or SAC classification against the notification in force on the invoice date.
- Issue a debit or credit note under Sec. 34 for the differential tax and report it in the return for the period.
- Fix the item master so the same classification does not repeat.
Test this on a real register
Upload a sales or purchase file in the free simulator — no sign-up — and see every finding with the clause it breaches and the rupee impact. In the signed-in workspace, firm owners and admins can reconcile the books and use the approved figures to prepare and file GSTR-1 or GSTR-3B by EVC.