Editing ABA routing transit number (section)

===Fraction format===
The fraction form looks like a [[fraction (mathematics)|fraction]], with a [[numerator]] and a [[denominator]].

The numerator consists of two parts separated by a dash. The prefix (no longer used in check processing, yet still printed on most checks) is a 1 or 2 digit code (P or PP) indicating the region where the bank is located. The numbers 1 to 49 are cities, assigned by size of the cities in 1910. The numbers 50 to 99 are states, assigned in a rough spatial geographic order, and are used for banks located outside one of the 49 numbered cities.

The second part of the numerator (after the dash) is the bank's ABA Institution Identifier, which also forms digits 5 to 8 of the nine digit routing number (YYYY).

The denominator is also part of the routing number; by adding leading zeroes to make up four digits where necessary (e.g. 212 is written as 0212, 31 is written as 0031, etc.), it forms the first four digits of the routing number (XXXX).

There might also be a fourth element printed to the right of the fraction: this is the bank's branch number. It is not included in the MICR line. It would only be used internally by the bank, e.g. to show where the signature card is located, where to contact the responsible officer in case of an overdraft, etc.

For example, a check from Wachovia Bank in Yardley, PA, has a fraction of 55-2/212 and a routing number of 021200025. The prefix (55) no longer has any relevance, but from the remainder of the fraction, the first 8 digits of the routing number (02120002) can be determined, and the check digit (the last digit, 5 in this example) can be calculated by using the [[#Internal checksums|check digit formula]] (thus giving 021200025).

====ABA prefix table====
This table is up to date as of 2020. One weakness of the current routing table arrangement is that various territories like American Samoa, Guam, Puerto Rico and the US Virgin Islands share the same routing code.

{| class="wikitable"
|-
! Prefix
! Location
|-
| 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
|-
| 17
|  Minneapolis, MN
|-
| 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
| Hawaii
|-
| 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
|-
| 82
| Colorado
|-
| 83
| Kansas
|-
| 84
| Louisiana
|-
| 85
| Mississippi
|-
| 86
| Oklahoma
|-
| 87
| Tennessee
|-
| 88
| Texas
|-
| 89
| Alaska
|-
| 90
| California
|-
| 91
| Arizona
|-
| 92
| Idaho
|-
| 93
| Montana
|-
| 94
| Nevada
|-
| 95
| New Mexico
|-
| 96
| Oregon
|-
| 97
| Utah
|-
| 98
| Washington
|-
| 99
| Wyoming
|-
|101
|American Samoa, Guam, Puerto Rico, Virgin Islands
|}