Online, my bank shows that I have two balances, one is what has cleared, the other what is pending.
When I balance my account, I only look at what has cleared, this is the same balance that would appear on the paper copy. I then add/subtract outstanding checks/debit card purchases and deposits.
The pending balance may not always be accurate. For example, if you go out to eat and the bill is $29.99 and you pay with your debit card, and add a tip of $5, for a total of $34.99. The pending balance at first may only show the debit as $29.99. When you sign the charge slip? They have only submitted the cost of the meal...you are adding the tip afterwards. So they usually submit the tips at the end of the servers shift. Some places do it the next day. So, that could be where a few dollars go missing. There may be other instances that this happens,but this is probably the most common.