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Q: ABA routing algorithm ( Answered ,   1 Comment )
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 Subject: ABA routing algorithm Category: Computers > Algorithms Asked by: willgreenhalgh-ga List Price: \$2.00 Posted: 21 Jul 2002 23:01 PDT Expires: 20 Aug 2002 23:01 PDT Question ID: 43619
 ```What is the algorithm used to create ABA routing numbers.? How do they check/create the nine numbers between the |:'s on checks?```
 ```Greetings! What an interesting question - I did not even know they had a checksum until I began researching this question. The algorithm to check the ABA Routing Number is as follows: We'll start with a routing number like 789456124. Here's how the algorithm works. First, strip out any non-numeric characters (like dashes or spaces) and makes sure the resulting string's length is nine digits, 7 8 9 4 5 6 1 2 4 Then we multiply the first digit by 3, the second by 7, the third by 1, the fourth by 3, the fifth by 7, the sixth by 1, etc., and add them all up. (7 x 3) + (8 x 7) + (9 x 1) + (4 x 3) + (5 x 7) + (6 x 1) + (1 x 3) + (2 x 7) + (4 x 1) = 160 If the resulting number is an integer multiple of 10, then the number is valid. To calculate what the checksum digit should be, follow the above algorithm for the first 8 digits. In the case above, you would come up with 156. Thus, to make the total number an integer multiple of 10, the final check digit must be 4. From BrainJar.com: Validation Algorithms http://www.brainjar.com/js/validation/ The above page also gives a JavaScript code sample for validating the numbers. The numbers are acutally created by the ABA, and in general, the first four digits are a Federal Reserve routing symbol, identifying which of the twelve Federal Reserve districts the check was printed in (and a city within that district). The next four digits are an ABA institution identifier which designates the bank on which the check is drawn, and the last number is a check digit. From Urban Legends Reference Pages: Business (Check and Double Check) http://www.snopes2.com/business/bank/number.htm You can read further about the ABA routing numbers and their background at the ABA website: http://www.aba.com/Products/PS98_Routing.htm The complete Routing Number Policy is found in this PDF file: http://www.tfp.com/text/ABApolcy.pdf If you would like the complete key to all ABA Routing Numbers, you can order it for \$169.00 from Thomson Financial Publishing at this page: http://www.tfp.com/order_US.shtml Additionally, you can find banks via their routing number at the Federal Reseve website: http://www.fedwiredirectory.frb.org/search.cfm I also found a Cold Fusion code snippet that validates ABA Routing Numbers at the Common Function Library Project http://www.cflib.org/udf.cfm?ID=552 Search Strategies: ABA routing number algorithm ://www.google.com/search?q=ABA+routing+number+algorithm```
 willgreenhalgh-ga rated this answer: ```Very thorough, well explained. I spent an hour and couldnt find a damb thing. I figured it was top secret or something.```
 ```Additionally, the first two digits of the routing number must fall within the range "01" through "12", or "21" through "32". These digits indicate the Federal Reserve District (there are twelve), with the latter set indicating that the bank is a "thrift institution". See FRB Regulation CC, Appendix A, which available online here: ```