Alix Axel Weblog

Yesterday I got my hands on my very first Lincoln (five dollars) bill, they seem much more older and used than Euro banknotes. As I had already made a Euro note serial number validation algorithm in PHP I thought: “why don’t I do the same for dollar bills?”.

I started by doing some research on Google for validation algorithms but nothing useful came up, so I asked a friend to give me the serial numbers of all the dollar bills he had (pre-1995 ones) and I started doing some math, using modulo operations and comparisons… I found some interesting things, but still no luck regarding a working validation algorithm…

I googled a couple of different expressions (by the way have you noticed that .cn domains are starting to bomb Google SERP’s really hard lately?) and found some cool stuff:

• There are more dollar banknotes other than $1, $2, $5, $10, $20, $50 and $100, such as $1/3 and the large denominations bills of $500, $1000, $5000, $10000 and $100000.
• Bills that were printed before 1996 have in the serial number 10 digits (1 letter, 8 digits and one more letter), all the following have 11 digits (2 letters, 8 digits and one more letter).
• The last letter in the serial number is sometimes a star (*), this means that the bill is a replacement for another which didn’t met the US Federal Reserve printing standards.

The first letter of post-1996 bills identifies the the currency series, you can also find the series on the bottom-right of the presidential portrait.

The second letter (or first if you are looking at a pre-1996 bill) represents the district (A to L) of the Federal Reserve Bank the bill was issued from.

• A - Boston
• B - New York
• C - Philadelphia
• D - Cleveland
• E - Richmond
• F - Atlanta
• G - Chicago
• H - St. Louis
• I - Minneapolis
• J - Kansas City
• K - Dallas
• L - San Francisco

The eight following digits are sequential and, as far as I’m aware of, don’t need to meet any specific format or mathematical formula. The last letter is also sequential however it cannot contain the value of “O” and, as referred above, can contain “*” if the bill is a replacement for another.

Based on this info I’ve coded a simple Dollar serial number validator in PHP, you can also try it online. Here are some tests:

• CB47511319A
• BE51693641C
• AK50403409A
• CB51139287A
• L11180916C
• DL88031383B
• C45752368C

Dollar bills can be digitalized and printed because they don’t have the EURion Constellation security measure. There is also an interesting pattern: the first letter of the short serial number (located under the serial number) is the same as the second (or first on a pre-1996 bill) letter of the serial number. I still haven’t been able to figure out what is the short serial used for.

I hope you like this function, if you know the check digit algorithm for dollar bills please let me know.

PS: If you live in a country with another currency and want a serial number validation algorithm please send me a sample note and I’ll code it for you.

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