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Deciphering Bank Routing Numbers

What Your Bank Account's ABA Number Means


Origin of Bank Routing Numbers

The American Bankers Association established ABA numbers in 1910. Each bank was assigned its own unique ABA number. Today ABA numbers are often referred to as RTN or Routing Transit Numbers. Most people outside the banking industry refer to them simply as the bank routing numbers. 


Common Use

Bank routing numbers can be found on the bottom of checks and deposit slips. In the lower left side or center of a check, there are 9 digits printed in magnetic ink. They are usually followed by the bank account account number. Banking institutions use online databases to identify a specific bank by entering the ABA number. The ABA number can also be identified by knowing which bank branch the account was opened at. All of the digits in the bank routing number have unique importance. Occasionally, banks may have seperate routing numbers for wire transfers and ACH transfers.


What Each of the Nine Digits Mean

  • The first four digits were initially assigned by the Federal Reserve Routing System and represent the bank's physical location. Because of acquisitions and mergers, these numbers frequently have no correlation to the banks geographic location today. 
  • The fifth and sixth digits designate which Federal Reserve bank the institution's electronic and wire transfers will route through. 
  • The seventh digit denotes which Federal Reserve check processing center was originally assigned to the bank. 
  • The eighth digit designates which Federal Reserve district the bank is in. 
  • The ninth digit provides a check sum. The check sum is a complicated mathematical expression using the first 8 digits. If the end result does not equal the check sum number, the transaction is flagged and rerouted for manual processing.
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