Unrecorded Fees, Interest, and Auto-Charges
The single most common reason an account fails to reconcile is a bank-originated transaction that was never entered in the books. Monthly service fees, transaction charges, interest, and automatic payments appear on the statement but are easy to overlook because you did not initiate them yourself. The fix is straightforward: scan the statement for any charge or credit not already in your records and enter it. Because these tend to recur, a rule that automatically records the predictable ones prevents the same small discrepancy from appearing every month.
Duplicates and Double-Entry
Recording the same transaction twice throws off the balance by exactly that amount. Duplicates creep in when a transaction is entered manually and then also imported by a bank feed, or when an import runs twice. They are among the easier errors to spot because the discrepancy equals the duplicated amount, and the duplicate usually sits right next to its twin. Good software flags likely duplicates automatically. When reconciling by hand, sorting by amount makes pairs of identical figures stand out so you can remove the extra entry.
Transposed and Mistyped Numbers
A classic manual error is transposing digits, entering 54 as 45, or mistyping an amount entirely. A useful clue for transposition is that the resulting discrepancy is divisible by nine, a quirk of how transposed digits affect the total. Mistyped amounts simply create a mismatch on the affected transaction. The defense against these errors is reducing manual entry in the first place: when transactions import directly from the bank, the amounts are correct by definition, and the opportunity to fat-finger a figure largely disappears.
Confusing Timing Differences With Errors
Not every difference is a mistake. Outstanding payments and deposits in transit cause legitimate, temporary gaps between your books and the statement. A common error is to treat these timing differences as problems and start adjusting entries that were actually correct, which creates new errors. The discipline is to maintain a clear list of outstanding and in-transit items and confirm they clear in the following period. If an item never clears, that is worth investigating, but until then it is simply a timing difference, not an error to fix.
Wrong Starting Balance and Missing Entries
Two structural errors derail a reconciliation before it begins. Reconciling against the wrong opening balance, often because the prior period was not properly closed, means the math can never tie out no matter how carefully you match. The fix is to confirm the previous reconciliation was completed and locked. The other is a transaction entirely missing from the books, which matching cannot reveal because there is nothing to match against. Reviewing the statement for any cleared item with no counterpart in your records catches these, and frequent reconciliation keeps the search small.