BANK ROUTING NUMBERS - THE ANATOMY OF

The routing number is a number used by financial institutions to designate the physical bank for which a negotiable instrument has been drawn from. The routing number does not indicate an individual.

United States Bank Routing Numbers

The routing number is derived from the bank's transit number originated by the American Bankers Association. The terms used in the industry are routing transit number (RTN), or routing number. The routing number is a nine digit number, used in the United States, which appears on the bottom of negotiable instruments, such as checks, that identifies which financial institution it is drawn upon. This code is also used by the Automated Clearing House (ACH) to process direct deposits and other automated transfers.

The American Bankers Association has assigned transit numbers through registrars, currently Accuity is the company responsible for assigning new ABA numbers. Accuity publishes the ABA Number Directory in the American Bankers Association Key to Routing Numbers semi-annually.

There are approximately 28,000 active routing and transit numbers currently in use. Every financial institution in the United States has one of these.

The ABA transit number generally appears in the upper right part of a check near the date. It looks like a fraction, with a numerator and a denominator. The denominator is identical to the first four digits of the routing number. The numerator consists of two parts. The prefix is a one to three digit code indicating the region where the bank is located. The numbers 1 to 49 are cities. The numbers 50 to 99 are states. They are used for banks located outside one of the 49 numbered cities. There might be a fourth element to the ABA number, a branch number, at either the end of the transit number or to the right of it.

The routing number consists of 9 digits: XXXXYYYYC

where XXXX is Federal Reserve Routing Symbol, YYYY is ABA 

Institution Identifier, and C is the Check Digit

The first two digits of the nine digit ABA number must be in the ranges 00 through 12, 21 through 32, 61 through 72, or 80.

The digits are assigned as follows:

• 00 is used by the United States Government

• 01 through 12 are the "normal" routing numbers

• 21 through 32 were assigned only to thrift institutions (e.g. credit unions and savings banks) through 1985; currently are still used by the thrift institutions or their successors

• 61 through 72 are used for electronic transactions

• 80 is used for traveler's cheques

The number must pass a checksum test using a position-weighted sum of each of the digits.

The following condition must hold: (3(d1 + d4 + d7) + 7(d2 + d5 + d8) + 1(d3 + d6 + d9))mod 10 = 0. (Mod or modulo is the remainder of a division operation.)

The following formula can be used to generate the 9th digit in the checksum:

(10 − (3(d1 + d4 + d7) + 7(d2 + d5 + d8) + 1(d3 + d6))mod 10)mod 10 = d9

Canadian Routing Numbers

Canadian transit numbers are regulated by the Canadian Payments Association. A number has the following form: XXXXX-YYY

Where XXXXX is a Branch Number, and YYY is an Institution Number. The dash between the branch number and the institution number is an integral part of the transit number.

As a general rule, Bank institution numbers start with 0, 2, 3, or 6, Credit Union and Caisse Populaire Institution numbers start with 8, and Trust Company institutions numbers with 5.

In a Canadian bank transit number the last digit of the branch number, with few exceptions, indicates the geographical location of the branch.

International Bank Routing Numbers

Australia has a six-digit prefix to a bank account number that indicates the bank and branch of the account. The prefix is known as the "Bank State Branch" or BSB code.

The UK uses a six digit "sort code".