Every batch, the same five mistakes show up in the first reconciliation a fresher prepares. None of them are about knowing the law — they are about habits. Fix the habits early and the rest follows.
1. Reconciling against GSTR-2A instead of 2B
Input tax credit is claimed on the basis of GSTR-2B, the static statement. 2A keeps changing as suppliers file late. Always freeze your working on 2B for the period, and treat 2A only as an early warning.
2. Forgetting credit and debit notes
A purchase register that matches 2B on invoices can still be wrong once supplier credit notes are applied. Pull notes into the same sheet, net them per supplier, then compare.
3. Matching on invoice number alone
"INV/023", "023" and "INV-23" are the same invoice to a human and three different ones to a lookup. Match on supplier GSTIN plus a cleaned invoice number plus taxable value, in that order.
Build one helper column that strips spaces, slashes and leading zeros from invoice numbers. It removes most false mismatches before you start.
4. Ignoring place of supply
An intra-state purchase billed with IGST will not sit in the right bucket, and the credit can be questioned. Check the tax head against the supplier's state code on every exception line.
5. Not writing down the follow-up
A reconciliation is only useful if someone chases the mismatches. End every working with a short list: supplier, amount, issue, who is following up, and by when.
These are the exact checks our Job Oriented Course students run on live files from week one — so by the time they join a firm, reconciliation is routine rather than a risk.