Book balance is the cash balance shown in a company's own general ledger Cash account, reflecting every deposit, check, and electronic transaction the company itself has recorded, whether or not those items have yet cleared at the bank. It stands opposite the bank's own figure, the balance per bank, which reflects only the transactions the bank has actually processed as of a given date.
Why book balance and bank balance rarely match exactly
A company typically records a sale and the resulting cash receipt, or writes a check to a supplier, before the bank actually processes that transaction, which means the book balance moves first and the bank's figure catches up a few days later. Outstanding checks the company has already recorded but the bank has not yet paid, and deposits in transit the company has recorded but the bank has not yet posted, are the two most common reasons book balance and bank balance diverge on any given day.
Items the bank knows about before the books do
The reverse timing gap also happens: a bank may deduct a service charge, process a customer's bounced check, or add interest earned to the account before the company has had a chance to record any of those items in its own books. Until the company catches up and records them, its book balance will not yet reflect activity the bank statement already shows.
Reconciling the two figures
A bank reconciliation is the formal process of adjusting both the bank balance and the book balance for these known timing differences until the two arrive at the same adjusted figure, which represents the true cash position of the company at that date. Once reconciled, any remaining unexplained difference signals a genuine error, or in rare cases fraud, that needs to be investigated rather than simply assumed away as a timing issue.
Why book balance matters day to day
Because the book balance already reflects transactions the company knows about but the bank has not yet processed, it is usually the more accurate figure for the company's own internal cash management decisions, such as whether it is safe to write another check or make another payment, even though the bank's own figure is what ultimately determines whether a payment actually clears without triggering an overdraft.
A simple worked example
A company's book balance might show $18,200 after recording a $1,500 deposit and a $900 check written the same week, while the bank statement, not yet having processed either item, still shows $17,600. Once both items clear the bank in the following days, both figures converge on the same true $18,200 balance, illustrating why the book balance is usually the more current of the two figures on any given day.
Why neither balance alone tells the full story
Neither the book balance nor the bank's own statement balance is automatically “wrong” when the two differ; the gap usually just reflects transactions one side knows about that the other has not yet recorded or processed. A bank reconciliation starts from both figures and adjusts each for the items the other side is missing — deposits in transit and outstanding checks on one side, bank fees and interest the company has not yet recorded on the other — until both numbers are brought to the same true, adjusted cash balance that should actually appear on the company's balance sheet.