Bank Routing Numbers are essentially sequences of nine-digit numeric code (eight digits and one check digit) used to facilitate the transfer of funds. These number strings are also called Routing Transit Numbers (RTN), or American Bankers Association (ABA) Number. It was designed in 1910, but continues to be used today. Note that other countries may use different number formats.
A bank routing number – also referred to as Routing Transit Number (RTN) or ABA Routing Number – is a nine-digit numeric code (eight digits and one check digit) printed on the bottom of checks
Originally, these numbers were used by bank personnel to identify check processing endpoints. Today however, these numbers are printed in machine-readable magnetic ink, enabling faster processing and also improved security, benefiting not only those working in banks, but the average Love Money using consumer. The numbers are then used by the Automated Clearing House to verify checks and also record such transfers.
The bank routing number appears twice on a check. The first is the fraction form, found towards the upper-middle-right, or somewhere near the date field. It looks something like AA-BBBB/CCCC, and so it is called the fraction form. There may also be a branch number underneath it. The AA part is a prefix of two numbers that denote a location, though it is no longer used in processing. The BBBB part is the ABA Institution Identifier, or the ID number of the institution as assigned by the ABA. The CCCC section is the Federal Reserve Routing Symbol, which identifies both geographical location and also the type of institution.
At the bottom of the check, there is a series of numbers and other symbols. These are printed in a special ink that makes it possible for machines to read them, thus it is called the Magnetic Ink Character Recognition or MICR form of the bank routing number. The first 9-digit string is the Bank Routing Number, with the form CCCCBBBBD. The CCCC and BBBB are the same as in the fraction form. The single digit at the end, D, is a check digit. The check digit is used to verify the other numbers mathematically.
The check digit reduces the chances of money being sent to the wrong bank, and also works to provide some countermeasure against check fraud. Typically, a check where the MICR form is evaluated as “wrong” as per calculations using the numbers is automatically set aside for inspection and repair or further investigation.
Every six months, the ABA via Accuity publishes a codex containing all the routing numbers for banks and other financial institutions across the country. These codices contain all 22,000-plus active bank routing numbers in the Automated Clearing House database. Every financial institution in America has at least one of these numbers to their name.
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