Trace the Transaction Behind an Incorrect Balance
Begin with the last period that reconciled correctly and work forward until the difference first appears. Comparing statement activity with the account register narrows the search. The difference may come from one entry, several smaller entries or a starting balance, so avoid assuming a single transaction caused it.
Use the difference as a clue
A discrepancy equal to a known payment may suggest a missing or repeated entry. A difference that is twice a transaction amount can suggest a sign or direction problem. These are investigation clues, not proof. Search the actual records and verify dates, amounts and account assignments before making a correction.
Check connections between accounts
Transfers, credit card payments and loan payments affect more than one part of the books. A transfer entered as an expense may leave both a misleading profit report and an unreconciled receiving account. Review the paired activity rather than fixing only the account where the difference was noticed.
Avoid the unexplained balancing entry
Suppose your books are $900 below the statement because a supplier payment was entered twice. Adding $900 of miscellaneous income would make the cash number match but distort revenue and leave the underlying duplicate in place. Correct the supported cause, preserve a note and rerun the relevant reports. The finished reconciliation should explain the difference, not merely conceal it.