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“Fascinating” ABA Routing Number Facts
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So I was trying to figure out how long ABA Routing Numbers are valid for and accidentally unearthed a whole slew of facts I never knew about the little digits identifying your bank on your checks:
ABA stands for American Bankers Association and they come up with the ABA Routing Numbers, here’s a boring and long PDF file all about it.
What do the numbers stand for?
The first four numbers are the Federal Reserve routing symbol, which specifies which of the twelve Federal Reserve banks (including city) that the check was printed at. The next four digits specify your bank and the last digit is the checksum digit, a calculation I explain next.
Did you know that there is a checksum validity test?
For the non-nerds out there, a checksum just means you basically add the numbers together after doing some other mathy stuff and the result is a checksum. It’s a way to figure out if something was corrupted in the communication. To calculate the checksum for the ABA Routing Number, multiply the first digit by 3, the next by 7, the next by 1, and then repeat in that order. A valid ABA Routing Number’s checksum will be evenly divisible by 10.
So if you take Emigrant Direct’s ABA Routing number of 226070319:
Looking for a Bank With Its Routing Number?
Ta da! You can look it up at a Federal Reserve Financial Services website. I wonder if they give better rates at ABA#: 2839-7842-5.
I’m sure there are other great ABA facts but those are some to get you started.
{ 8 comments, please add your thoughts now! }
Checksum, nice.
Neat! I guess that’s how websites know if you’ve keyed in something valid?
Credit cards also use checksums:
http://www.beachnet.com/~hstiles/cardtype.html
hey wow, i didnt know about this checksum thing.
i dont know why but I just calculated my checking account’s routing number, just to see if it’s true. talk about productivity.
nice link Jay.
I hadn’t done that, but I have had to manually multiply out the individual characters of auto VINs to see if they’re actually valid or if our checksum routine was off.
A little more precise info about the checksum…
The 9th (last) digit of the 9-digit routing number is actually the “check digit”.
1. Take the first 8 digits and run the formula just as described in the article:
226070319:
(2 x 3) + (2 x 7) + (6 x 1) + (0 x 3) + (7 x 7) + (0 x 1) + (3 x 3) + (1 x 7) = 91
2. Divide that number by 10 and take the remainder (91 modulus 10, for math geeks) = 1
3. Subtract that remainder from 10. 10 – 1 = 9.
4. That should always equal the last digit, aka the check digit.
Checksums are used in other cases when it is critical to have accuracy. The 10 digit ISBNs (International Standard Book Number) identifying book titles use this. As I recall the general facts, the first group is the language (0=English); the next group is the publisher (I’m looking at a Penguin book=525); the third group is the individual unique title (Al Franken’s ‘Lies’ = 94764); the last group and single digit is the checksum (7). Sometines the groups are separated by hyphens, sometimes not. Ironically, I do not remember the formula for achieving the checksum! Perhaps someone can provide this?
Cool but does anyone know how to calculate the fraction form? Where do you get the city or state prefixes?