ABA Routing Number has 9 digits. The first 8 digits represent a specific bank or organization. And the last digit is Check Digit.

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: http://www.bankersonline.com/regs/229/a229a.html

The Check Digit is computed using Modulus 10 as follows:

Step 1: Multiply each digit in the Transit Routing Number by a weighting factor. The weighting factors for each digit are:

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Position: 1 2 3 4 5 6 7 8 
Weights: 3 7 1 3 7 1 3 7 </font>

Step 2: Add the results of the eight multiplications.

Step 3: Subtract the sum from the next highest multiple of 10. The result is the Check Digit.

Example:

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Transit/ABA    0 7 6 4 0 1 2 5 
Multiply by    <u>3 7 1 3 7 1 3 7</u> 
Add:        0 49 6 12 0 1 6 35 

Sum = 109 
Check Digit = 1 (110 minus 109)
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