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What is a TRANSIT/ABA Routing Number ?

TRANSIT/ABA Routing Number – 9-digit number assigned to a financial institution. Consists of the 4-digit Federal Reserve Routing Number followed by the 4-digit ABA Member Bank number followed by a check digit.

The ABA RTN appears in two forms on a standard check – the fraction form and the MICR (magnetic ink character recognition) form.  Both forms give essentially the same information, though there are slight differences.

The MICR forms are the main form – it is printed in magnetic ink, and is machine-readable; it appears at the bottom left of a check, and consists of nine digits.

The fraction form was used for manual processing before the invention of the MICR line, and still serves as a backup in check processing should the MICR line become illegible or torn; it generally appears in the upper right part of a check near the date.

The MICR number is of the form

XXXXYYYYC

where XXXX is Federal Reserve Routing Symbol, YYYY is ABA Institution Identifier, and C is the Check Digit, while the fraction is of the form:

PP-YYYY/XXXX

where PP is a 1 or 2 digit Prefix, no longer used in processing, but still printed, representing the bank’s check processing center location, with 1 through 49 for processing centers located in a major city, and 50 through 99 representing processing is done at a non-major city in a particular state. Sometimes a branch number or the account number are printed below the fraction form; branch number is not used in processing, while the account number is listed in MICR form at the bottom. Further, the Federal Reserve Routing Symbol and ABA Institution Identifier may have fewer than 4 digits in the fraction form. The essential data, shared by both forms, is the Federal Reserve Routing Symbol (XXXX), and the ABA Institution Identifier (YYYY), and these are usually the same in both the fraction form and the MICR, with only the order and format switched (and left-padded with 0s to ensure that they are 4 digits long).

The prefix and the Federal Reserve Routing Symbol (XXXX) are determined by the bank’s geographical location and treatment by the Federal Reserve type, while the remaining data (YYYY, and Branch number, if present) depends on the specific bank, and are unique within a Federal Reserve district.

In the check depicted above right, the fraction form is 11-3167/1210 (with 01 below it) and MICR form is 129131673 which are analyzed as follows:

  • the prefix 11 corresponds to San Francisco,
  • 3167 (common to both) is the ABA Institution Identifier,
  • 1210 and 1291 are the Federal Reserve Routing Symbols (generally equal, here different probably due to obfuscation, see image file history for more information), with the initial “12” corresponding to the Federal Reserve Bank of San Francisco, the third digits (“1” and “9”) corresponding to check processing centers, and the fourth digits (“0” and “1”) corresponding to where the bank is located – “0” indicates “in the Federal Reserve city of San Francisco”, while “1” indicates “in the state of California”.
  • the final “3” in the MICR is the check digit, and
  • the “01” below the fraction form is the branch number.

In the case of a MICR line that is illegible or torn, the check can still be processed without the check digit. Typically, a repair strip or sleeve is attached to the check, then a new MICR line is imprinted. Either 021200025 or 0212-0002 (with a hyphen, but no check digit) may be printed, and both are 9 digits. The former (with check digit) is preferred to ensure better accuracy, but requires computing the check digit, while the latter is easily determined by inspection of the fraction, with minimal clerical handling.

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