Karl (![[info]](http://web.archive.org/web/20070921204935im_/http://stat.livejournal.com/img/userinfo.gif){kind=small} supersat) wrote in supersat_tech,@ 2003-12-05 07:51:00 |
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Inside Check Numbers
As a follow-up to my previous post on credit card account numbers, I decided to document what the funny-looking numbers at the bottom of your checks represent, including how to calculate the check digits.
MICR
First, you might be wondering exactly why the numbers are printed in such a weird font. The reason lies in how these numbers are read. Back in the 70s, when the current routing system was devised, computers were unable to optically recognize characters. A technology called Magnetic Ink Character Recognition (MICR) was created to allow computers to read these characters. As a check goes through a MICR reader, the ink (containing ferrous metals) is magnetized. The ink then passes over a read head, similar to one used in tape players. Each character gives off a unique waveform that can easily and uniquely identify the character being passed over the read head. Therefore, each character was designed in such a way so that it gives off a unique waveform, yet is still human-readable.The Routing Number
The routing number, contained between the two routing/transit start/stop symbols (
), is made up of the following components:
| XXXXYYYYZ | |
| XXXX | Federal Reserve Routing Symbol |
| YYYY | American Bankers Association Institution ID |
| Z | Check digit |
The Federal Reserve Routing Symbol
Usually, the first two digits of the Federal Reserve Routing Symbol indicate which of the twelve federal reserve districts the bank is in. Numbers in the range of 21 to 32, indicate a "thrift institution," although assignment of these numbers was ended in 1985. To get the Federal Reserve district number from one of these numbers, simply subtract 20. For example, if the first two digits is 32, it indicates it is a "thrift institution" in the 12th Federal Reserve district (the western US). Routing symbols that start with 00 indicate the check is issued by the US government (except federal banks). Routing symbols that start with 80 are reserved for travelers checks, and all others are reserved.The third digit of the Federal Reserve Routing Symbol indicates which branch office of the district the check should be routed through. A 1 indicates the main office of the district, with digits 2-5 indicating a branch office. For example, in the 12th Federal Reserve district (the western US), 1 indicates San Francisco, 2 indicates Los Angeles, 3 indicates Portland, 4 indicates Salt Lake City, and 5 indicates Seattle.
The forth digit indicates the availability of funds. A 0 indicates immediate availability, a 1-5 indicates which state in the district the paying bank is located, and a 6-9 indicates a special collection arrangement.
The Federal Reserve Routing Symbol is the denominator in the transit number printed in the top-right corner of a check.
The ABA Institution ID
The full ABA institution ID is actually made up of two parts, separated by a dash. You can find the full ABA institution ID printed in the upper-right hand corner of your checks, as the numerator in the transit number. For example, it may look like: 96-1234. The part before the dash (the prefix) indicates the city or state the bank is located in. Numbers from 1 to 49 represent cities, while numbers from 50 to 99 indicate states. For states, numbers 50-58 represent eastern states, 59 represents Alaska, Hawaii, and US territories, 60-69 represent southeastern states, 70-79 represent central state, 80-88 represent southwestern states, and 90-99 represent western states.A full list of the ABA prefixes:
1 New York, NY 2 Chicago, IL 3 Philadelphia, PA 4 St. Louis, MO 5 Boston, MA 6 Cleveland, OH 7 Baltimore, MD 8 Pittsburgh, PA 9 Detroit, MI 10 Buffalo, NY 11 San Francisco, CA 12 Milwaukee, WI 13 Cincinnati, OH 14 New Orleans, LA 15 Washington D.C. 16 Los Angeles, CA 18 Kansas City, MO 19 Seattle, WA 20 Indianapolis, IN 21 Louisville, KY 22 St. Paul, MN 23 Denver, CO 24 Portland, OR 25 Columbus, OH 26 Memphis, TN 27 Omaha, NE 28 Spokane, WA 29 Albany, NY 30 San Antonio, TX 31 Salt Lake City, UT 32 Dallas, TX 33 Des Moines, IA 34 Tacoma, WA 35 Houston, TX 36 St. Joseph, MO 37 Fort Worth, TX 38 Savannah, GA 39 Oklahoma City, OK 40 Wichita, KS 41 Sioux City, IA 42 Pueblo, CO 43 Lincoln, NE 44 Topeka, KS 45 Dubuque, IA 46 Galveston, TX 47 Cedar Rapids, IA 48 Waco, TX 49 Muskogee, OK 50 New York 51 Connecticut 52 Maine 53 Massachusetts 54 New Hampshire 55 New Jersey 56 Ohio 57 Rhode Island 58 Vermont 59 Alaska, American Samoa, Guam, Hawaii, Puerto Rico, Virgin Islands 60 Pennsylvania 61 Alabama 62 Delaware 63 Florida 64 Georgia 65 Maryland 66 North Carolina 67 South Carolina 68 Virginia 69 West Virginia 70 Illinois 71 Indiana 72 Iowa 73 Kentucky 74 Michigan 75 Minnesota 76 Nebraska 77 North Dakota 78 South Dakota 79 Wisconsin 80 Missouri 81 Arkansas 83 Kansas 84 Louisiana 85 Mississippi 86 Oklahoma 87 Tennessee 88 Texas 90 California 91 Arizona 92 Idaho 93 Montana 94 Nevada 95 New Mexico 96 Oregon 97 Utah 98 Washington 99 Wyoming
The second part of ABA institution ID is limited to 4 digits, and is included in the MICR routing number. Since there are more than 10,000 institutions in the US, this number is obviously not unique to an institution. However, it is assigned so that it is unique inside the ABA prefix and Federal Reserve branch office area. Therefore, its meaning is not ambiguous inside the MICR routing number.
The Check Digit
The check digit ensures the number was read or keyed in without error. The algorithm used to compute the check digit of the routing number is as follows:Take the first, fourth, and seventh digit, multiply them by 7, and add them to the total.
Take the second, fifth, and 8th digit, multiply them by 3, and add them to the total.
Take the third and sixth digit, multiply them by 9, and add them to the total.
The check digit is the 1s digit of the total. Note that if you take the check digit, multiply it by 9, and add it to the total, the sum will be evenly divisible by 10.
The Account Number
The account number precedes the ANSI "on-us" symbol (
). The check digit algorithm is the same as the one used to verify the routing number. However, because account numbers are of variable length, it can be somewhat tricky to determine which multiplier to use with what digit. The best way to go about it is to work backwards from the last digit of the account number, not including the check digit. Working backwards, the pattern of multipliers is 3-7-9. For example, if you have the account number 123456, you would compute the check digit like so:| Account Number | 1 | 2 | 3 | 4 | 5 | 6 |
| Multiplier | 9 | 7 | 3 | 9 | 7 | 3 |
| Product | 9 | 14 | 9 | 36 | 35 | 18 |
Sum of products = 121, which means the check digit is 1.
