I always balance my and my husband's checkbook monthly. Banks do make mistakes. (I worked in one for 20 year) I find it easiest if I balance the book the same day I get the statement (I get my statement online - no paper). I print out the statement so I can take a pen and mark each transaction off the statement and my checkbook. Then I add any deposits/credits that the bank has not yet processed to the statement, substract any checks/debits that have not yet processed. If I do not balance it is usually one amount which can be found pretty easily. Usually takes about 10 minutes.