Traditionally, routing numbers appear in the bottom left corner of every check a customer writes. Because this account information doesn't change, it's printed on checks during manufacturing. A check's routing number is the first string of nine digits in the numbers that identify the account. The remaining numbers identify the account internally in the payor bank. The first four digits in routing numbers identify the bank's reserve district and identify the type of institution -- bank or thrift -- that issued the check. The other digits are assigned by the American Banker's Association to identify individual financial institutions.
Check Card Numbers
Because debit and check cards use systems developed by credit card companies rather than check-cashing technology, they don't incorporate routing numbers into the card. This system provides each holder with a unique account number and uses the first six digits of the number to identify the industry that issued the card -- typical industries are banking, airlines and telecommunications companies -- as well as identify the card's issuer, such as Visa or MasterCard. Most of the remaining digits serve as the check card's unique account number, with the final digit serving as a key for checking the account numbers against a verification algorithm. In many cases, the card account number is different from the checking or savings account number from which it draws funds.
Determining Routing Numbers
In some cases, such as when requesting funds to be deposited directly into an account from which an check card draws, customers must provide routing number information. Rather than refer to a check card, they should seek the information from the face of one of their checks. If the account holder only uses ATM withdrawals and electronic transfers and doesn't write checks, he should contact his bank to obtain the routing number and account number for the account associated with the card.
In addition to using a numbering system that makes check cards compatible with the existing credit-card numbering and identification system, maintaining a number different from a checking account's routing and account information adds a layer of security to the card. If the card is lost or stolen, the issuer can simply issue a new card with a different number to the cardholder. If the number were unique with the account number -- which is checked against individual check numbers when checks are written -- an account holder would need an entirely new account if his number became compromised.