GSTR-2B is an auto-generated, read-only statement that tells a buyer how much input tax credit is available for a tax period, compiled from the GSTR-1 (and other) filings of their suppliers. Because it is static for a period, it gives a stable basis for claiming ITC.
Reconciling your purchase records against GSTR-2B — matching what you recorded to what suppliers actually reported — is how you avoid claiming credit you are not entitled to, and chase suppliers who have not filed.
The statement is compiled once the filing window for a month closes, drawing on suppliers' GSTR-1 and IFF submissions along with import data from ICEGATE. Anything a supplier files after the cut-off simply rolls into your next month's statement, which is why credit can appear a period later than the purchase itself. Within the statement, entries are sorted into credit that is available and credit flagged as not available, for instance where the time limit has lapsed or the place of supply rules bar the claim.
Reconciliation is a line-level exercise: each purchase in the books is matched to a statement entry on the supplier's GSTIN, document number, date and tax amount. The output is four buckets — matched, mismatched on value, booked but missing from the statement, and appearing in the statement but never booked. Credit notes reported by suppliers also land here and reduce the credit available, so a reconciliation that only looks at invoices will overstate what can be claimed.
The recurring mistakes are practical ones: claiming credit straight from the purchase register without checking the statement, ignoring the not-available section, and treating GSTR-2A and GSTR-2B as interchangeable when one moves and the other does not. The costliest habit is postponing follow-up — a supplier who never files must be chased while the time limit for claiming that credit, as notified, is still open, not discovered during a year-end clean-up.