# ABA Routing Number Key: `finance.banking.aba_routing` US ABA (American Bankers Association) routing transit number. 9-digit identifier for financial institutions in the US Federal Reserve system. First two digits are a valid Federal Reserve prefix (01-12, 21-32, 61-72, 80). The 9th digit is a weighted checksum (weights 3,7,1 repeating, sum mod 10 = 0). Page: Samples: `021000021`, `111000025`, `021200025`, `071000013`, `011401533`, `121000358` ## Background ### Origin The routing number was devised by the American Bankers Association (ABA) in 1910 and adopted by the industry in 1911.[[1]](https://risk.lexisnexis.com/global/-/media/files/financial%20services/articles/lnrs-routing_number_policy-v2.pdf) The ABA developed the system to facilitate the sorting, bundling and delivering of paper cheques to the drawer's bank for debit to the drawer's account.[[2]](https://en.wikipedia.org/wiki/Routing_transit_number) Before the numbers existed, banks had been disagreeing on identification.[[2]](https://en.wikipedia.org/wiki/Routing_transit_number) The ABA arranged a meeting of clearing house managers in Chicago in December 1910.[[2]](https://en.wikipedia.org/wiki/Routing_transit_number) The ABA released the codes in May 1911.[[2]](https://en.wikipedia.org/wiki/Routing_transit_number) In the original ABA numbering, lower prefixes were used for higher populations, based first on the 1910 US Census.[[2]](https://en.wikipedia.org/wiki/Routing_transit_number) In 1973 a joint task force of the American Bankers Association and the Federal Reserve System was formed to formally define the purpose of the routing number and the eligibility criteria for obtaining one.[[1]](https://risk.lexisnexis.com/global/-/media/files/financial%20services/articles/lnrs-routing_number_policy-v2.pdf) The 1973 task force's work culminated in 1976 in a policy statement and a set of guidelines for assigning and administering routing numbers.[[1]](https://risk.lexisnexis.com/global/-/media/files/financial%20services/articles/lnrs-routing_number_policy-v2.pdf) The Routing Number Administrative Board was created in June 1985 to administer the policy and procedures associated with routing numbers.[[1]](https://risk.lexisnexis.com/global/-/media/files/financial%20services/articles/lnrs-routing_number_policy-v2.pdf) The ABA's Routing Number Policy names LexisNexis Risk Solutions as the current Official Registrar of Routing Numbers.[[1]](https://risk.lexisnexis.com/global/-/media/files/financial%20services/articles/lnrs-routing_number_policy-v2.pdf) The ABA's Routing Number Policy states that the primary purpose of the routing number is to identify the bank which is responsible to either pay or give credit, or is entitled to receive payment or credit, for a check or electronic transaction.[[1]](https://risk.lexisnexis.com/global/-/media/files/financial%20services/articles/lnrs-routing_number_policy-v2.pdf) The ABA's Routing Number Policy allocates the 01-12 series of first two digits to the checks and electronic transactions of banks, Federal Home Loan Banks, Farm Credit Banks and state government units, among others.[[1]](https://risk.lexisnexis.com/global/-/media/files/financial%20services/articles/lnrs-routing_number_policy-v2.pdf) Routing numbers beginning 01 through 12 correspond to the 12 Federal Reserve Banks.[[2]](https://en.wikipedia.org/wiki/Routing_transit_number) The ABA's Routing Number Policy allocates the 21-32 series to the checks, drafts and electronic transactions of thrift institutions.[[1]](https://risk.lexisnexis.com/global/-/media/files/financial%20services/articles/lnrs-routing_number_policy-v2.pdf) The ABA discontinued assignment of 21-32 series numbers in 1985, and thrift institutions have since been assigned numbers in the 01-12 series.[[1]](https://risk.lexisnexis.com/global/-/media/files/financial%20services/articles/lnrs-routing_number_policy-v2.pdf) A thrift prefix corresponds to the normal Federal Reserve prefix plus 20.[[2]](https://en.wikipedia.org/wiki/Routing_transit_number) The ABA's Routing Number Policy allocates the 61-72 series to Electronic Transaction Identifiers.[[1]](https://risk.lexisnexis.com/global/-/media/files/financial%20services/articles/lnrs-routing_number_policy-v2.pdf) The ABA's Routing Number Policy says Electronic Transaction Identifiers may not appear on checks or drafts.[[1]](https://risk.lexisnexis.com/global/-/media/files/financial%20services/articles/lnrs-routing_number_policy-v2.pdf) The ABA's Routing Number Policy allocates the 80 series to traveler's checks.[[1]](https://risk.lexisnexis.com/global/-/media/files/financial%20services/articles/lnrs-routing_number_policy-v2.pdf) The ninth digit of a routing number is a check digit: 3 times the sum of digits 1, 4 and 7, plus 7 times the sum of digits 2, 5 and 8, plus the sum of digits 3, 6 and 9, must leave no remainder when divided by 10.[[2]](https://en.wikipedia.org/wiki/Routing_transit_number) The 3-7-1 weighting catches any single-digit error together with most transposition errors.[[2]](https://en.wikipedia.org/wiki/Routing_transit_number) The 3-7-1 weighting does not catch transpositions of two digits that differ by 5, such as 0 and 5.[[2]](https://en.wikipedia.org/wiki/Routing_transit_number) High-speed cheque-sorting equipment will typically verify the checksum and route an item that fails to a reject pocket for manual examination.[[2]](https://en.wikipedia.org/wiki/Routing_transit_number) ### Use On a cheque, the routing number is printed in magnetic ink as part of the machine-readable MICR line along the bottom.[[2]](https://en.wikipedia.org/wiki/Routing_transit_number) Newer electronic payment methods continue to rely on ABA routing numbers to identify the paying bank or other financial institution.[[2]](https://en.wikipedia.org/wiki/Routing_transit_number) Federal Reserve payment services use routing numbers to identify participants in the Fedwire Funds Service, Fedwire Securities Service and FedACH transactions.[[2]](https://en.wikipedia.org/wiki/Routing_transit_number) ABA routing numbers are only for use in payment transactions within the United States.[[2]](https://en.wikipedia.org/wiki/Routing_transit_number) Incoming international wire transfers also use a BIC, also known as a SWIFT code, defined by ISO 9362.[[2]](https://en.wikipedia.org/wiki/Routing_transit_number) The same bank may use different routing numbers for cheques and for wire transfers.[[2]](https://en.wikipedia.org/wiki/Routing_transit_number) The ABA's Routing Number Policy allows a bank up to nine additional routing numbers beyond its principal office number.[[1]](https://risk.lexisnexis.com/global/-/media/files/financial%20services/articles/lnrs-routing_number_policy-v2.pdf) The IRS's Form 1040 instructions tell filers to ask their financial institution for the correct routing number if the routing number on a deposit slip is different from the routing number on their cheques.[[3]](https://www.irs.gov/instructions/i1040gi) Expect one institution to appear under several routing numbers in a file, and match routing numbers to institutions through a directory rather than assuming one number per bank. (Meridian's view) Following consolidation in the banking industry and of the Federal Reserve's check processing, the routing number a financial institution uses may not reflect the Federal Reserve district where its place of business is located.[[2]](https://en.wikipedia.org/wiki/Routing_transit_number) Treat the first two digits as a numbering series rather than a reliable clue to where a bank is. (Meridian's view) Thomson Reuters' documentation of the ACH entry detail record places the first 8 digits of the 9-digit routing number in positions 04-11 and the last digit in position 12.[[4]](https://www.thomsonreuters.com/en-us/help/accounting-cs-client-access/direct-deposit/ach-structure-and-contents/ach-structure-and-content-1) When you take a routing number from a fixed-width ACH file, rejoin the eight-digit field with its check digit before you validate it. (Meridian's view) Bank of America's routing number for incoming wires in New York, 0260-0959-3, begins with 02 for the Federal Reserve Bank of New York.[[2]](https://en.wikipedia.org/wiki/Routing_transit_number) Keep routing numbers as nine-character text, never as integers, so that a leading zero survives every load and export. (Meridian's view) Validate in two steps: check the first two digits against the allocated series, then check the 3-7-1 checksum. (Meridian's view) The ABA's Routing Number Policy says an item bearing a retired routing number is subject to being rejected or returned.[[1]](https://risk.lexisnexis.com/global/-/media/files/financial%20services/articles/lnrs-routing_number_policy-v2.pdf) A value that passes both checks is well formed, not proof that the number is assigned and in use today. (Meridian's view) ### Where you'll meet it The IRS's Form 1040 instructions require a routing number of nine digits whose first two digits are 01 through 12 or 21 through 32 for direct deposit of a refund.[[3]](https://www.irs.gov/instructions/i1040gi) ## Sources 1. [American Bankers Association Routing Number Policy \& Procedures](https://risk.lexisnexis.com/global/-/media/files/financial%20services/articles/lnrs-routing_number_policy-v2.pdf) — standard 2. [Routing transit number](https://en.wikipedia.org/wiki/Routing_transit_number) — secondary source 3. [1040 (2025)](https://www.irs.gov/instructions/i1040gi) — organisation 4. [ACH file - entry detail record](https://www.thomsonreuters.com/en-us/help/accounting-cs-client-access/direct-deposit/ach-structure-and-contents/ach-structure-and-content-1) — documentation