History

• The routing number system was created by the American Bankers Association in 1910 to help sort, bundle and ship paper checks to the correct banks. As of October 2010, the routing number covers a system of around 28,000 financial institutions, plus automated clearinghouses, electronic funds transfers and online banking systems.
  
  

Format

• The routing number follows a specific, standardized format. The routing number on the top left of a check is a multi-digit fraction with a hyphenated numerator and a three- or four-digit denominator (e.g., 50-113/310). The number is also encoded in the magnetic ink character recognition (MICR) number at the bottom of a check. A MICR number allows computers to read account numbers from checks. The nine-digit number includes a check digit and has a machine-readable bar code beneath it.
  
  

Meaning of First Eight Digits

• The first two digits in the fractional routing number are a city or state prefix. For example, "59" stands for Hawaii; "90" through "99" represent California and surrounding states. The next three digits identify the banking institution, while the three digits after that make up the Federal Reserve Routing Symbol, which identifies the Federal Reserve bank. For example, the numbers "1291" identify the Federal Reserve Bank of San Francisco.
  
  

Meaning of Final "Check" Digit

• The final number in the nine-number sequence is a check digit, which a computer uses to make sure the previous eight digits have been read correctly and are valid. The first, fourth and seventh numbers in the bank routing number are multiplied by 3; then the third and sixth numbers are multiplied by 1. All eight products are added and then subtracted from the next multiple of 10. For example, if the multiplied check digits all add up to 99, then 100--99 = 1.
  
  

Caution

• Historically, numbers were assigned to banks and the Federal Reserve banks on a consistent and logical basis. However, you may not be able to trace all numbers back to their origins. For example, thrift banks (banks that took deposits and originated home mortgages) used to be assigned a unique number. That's no longer the case, so while many numbers can be traced to the correct thrift bank, others may now lead to Federal Reserve check-processing centers.