Your checking account has several numbers associated with it that are critical to ensuring your deposits are credited to your account, but you can easily mix them up. The most important numbers you need to know are your account number, and bank or routing number. You can find these on your checks, and in the case of your routing number, on the web.
Your account number refers to the string of digits identifying your account within an institution. The length of your account number can vary by institution and the type of account you have. If you have a checking account, the bank prints your account number on the bottom of your checks as the second number after your routing number. You can have the same account number at different institutions, but not the same account and routing number.
The first number listed on the bottom of your checks is a routing number, also called a bank number or transit number. A bank/transit number identifies your bank so when an institution receives a check it knows the institution to which it belongs. Routing numbers are always nine digits and assigned by the American Banking Association. A bank might have one transit number for all accounts, or a different transit number for each type of transaction, such as one for paper checks and one for electronic transfers.
Large, national banks usually segregate their accounts by region and have transit numbers assigned to customers in those locales. For example, Bank of America has separate routing numbers for customers in the northern and southern parts of Texas. If you enter an invalid routing number for a transaction, the bank or merchant will not be able to process it. If the routing number is for an existing bank, it will go through if the account number is valid too.
If you need your routing number, call your bank's customer service line or you can look it up at the RoutingNumbers.org database. Any zeros placed at the beginning or end of your account number are part of it, so include zeroes when you need to give out your account information. Shred any canceled checks. A thief can skim your routing and account number to create counterfeit checks and pass them off under your name.