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The ABA Bank Routing Number

Background and Development of the Numbering System

Prior to 1910, no uniform system existed to identify and route the growing number of drafts, checks and other payment documents passing among the nation's banks. It was not unusual to have several individual numbering schemes-each devised by a major Correspondent or money center bank-serving the same small region.

To simplify and speed up the increasingly complex payments system, the American Bankers Association developed, with the cooperation of it's members, a master plan for the numerical identification of financial institutions.This plan was adopted in 1911 by ABA's Executive Council, who at that time also authorized publication of a book containing the names of institutions participating in the payments system, and their assigned "identifier" numbers. Rand McNally was named the Association's assigning agent in 1911. Thomson Financial Publishing was appointed assigning agent in April, 1990, following its acquisition of Rand McNally's Financial Publishing Division. The Routing Number Administrative Board of the American Bankers Association governs the assignment, use and retirement of routing numbers.

Originally designed to identify only check processing endpoints (paying institutions) in paper payments processing, the routing number system has evolved today to a more flexible means of designating participants in automated clearing houses, electronic funds transfer and other types of settlement arrangements.

There are two forms of the routing number currently in use: the nine-digit machine readable or MICR (magnetic ink character recognition) form, and the older fractional form that was relied upon when checks were hand-sorted. Both appear on most checks and drafts today, although in automated item processing only the MICR form is used. The fractional version is used when the MICR number is damaged or unreadable.


In 1956, an improvement in check processing speed and efficiency was achieved by the adoption of machine-readable numbering for checks and drafts. By encoding items with a routing number in MICR-magnetic ink character recognition-form, banks could move to automated sorting and handling in their processing operations.

Generally speaking, checks are encoded with three sets of machine-readable numbers, all appearing across the bottom of the document: the routing number; the customer's account number and optional internal bank transaction codes (in what is called the "on-us" field); and the amount of the check. An additional number may be included on commercial or business checks containing the check number or other indicative data (in what is called the "auxiliary on-us field").


The fields identified above are printed at the bottom of the check in a band 5/8" deep. The fractional form of the routing number is still required in the upper right corner of the item to be in compliance with Federal Reserve requirements. The name, city and state of the drawee or originating institution identified by the routing number must also be printed on the document. For "payable through" checks, items must be labeled with the name, location and first four digits of the routing number of the bank at which the check is written and the legend "payable through" followed by the name and location of the payable through bank.

Rigid standards exist for the placement of the MICR number on checks, the location and arrangement of the characters, number of digits allowed within various fields of information, the sequence of these fields, and proper ink density specifications. Check standards are developed by the Accredited Standards Committee X9 and published by the American Bankers Association, 1120 Connecticut Avenue N.W., Washington, DC 20036.

Sample MICR Routing Number:


Federal Reserve

Routing Symbol    


 ABA Institution





A. Federal Reserve Routing Symbol

Because of the increasing volume of checks in use and resulting complications in their collection and processing, the routing symbol was added to the routing number in 1945 by the ABA and the Federal Reserve. Its purpose was to further identify the origin and routing pattern of an item by showing the Federal Reserve district, office and clearing arrangement used by the originating or drawee bank. Routing symbols were only assigned to eligible institutions whose items were collectible through Federal Reserve offices.

By adopting the routing symbol, ABA and Federal Reserve officials were striving for faster check sorting, more efficiency in collections and better (i.e. more specific) identification of originating institutions.

The routing symbol is composed of four digits, each with a special meaning:

The first and second digits designate the Federal Reserve district. The districts are numbered as follows:

01 Boston   07 Chicago
02 New York 08 St. Louis
03 Philadelphia 09 Minneapolis
04 Cleveland 10 Kansas City
05 Richmond   11 Dallas
06 Atlanta 12 San Francisco


In districts 1 through 9, a zero is placed before the number to use two positions in the routing symbol. As an example, in the routing symbol 0670, the 06 indicates that the institution is located in the sixth Federal Reserve district.

Until 1985, if the routing number was assigned to a thrift institution-a savings and loan association or credit union, for instance-a factor of 2 was added to the first position, e.g. 0 + 2 in Federal Reserve districts 1-9, 1 + 2 in districts 10, 11 and 12. To use the example above, then, the routing symbol would become 2670, indicating that it belonged to a thrift in the sixth Federal Reserve district. In 1985, the ABA Routing Number Administrative Board discontinued this requirement.

The third digit represents the particular office of a Federal Reserve Bank serving the presentment point identified by the routing number. The numbers 1 to 6 are used to identify offices of a Federal Reserve Bank. Occasionally, numbers 7 through 9 are used to denote special collection arrangements within a Federal Reserve District.

The fourth digit originally indicated when a collecting institution could expect to receive credit for an item collected through the Fed. The fourth digit identified geographic areas within the territory served by a Federal Reserve office. Since items could be presented faster to institutions in an area close to a Federal Reserve office, collecting banks received earlier credit for those items. Slower credit was granted on items that had to be presented in more distant areas. Thus a collecting institution could use the value of this fourth digit to estimate when it would receive credit for an item based on how quickly that item could be delivered to a paying institution's presentment point by the Fed office serving that territory.

In the current environment many other factors, besides proximity, can effect the timing of the presentment of items and when a bank will receive credit for an item collected through the Fed. To determine when it will receive credit for that item, a collecting bank must now use all four digits of the Federal Reserve Routing Symbol and refer to the published availability schedule for the Federal Reserve check processing region in which the item will be presented. Keybook readers should contact their local Federal Reserve Bank for information on how to obtain and use copies of these availability schedules.

A complete list of routing symbols by Federal Reserve district, branch, city and regional check processing center (RCPC) locations appears following this explanatory section.

See also:

B. ABA Institution Identifier

Working through Thomson Financial Publishing the American Bankers Association controls the master list and the assignment of the institution identifier. Each eligible financial institution receives a unique identifier comprising one to four digits. Because it rnust take four positions, the identifier is shown with zeroes added before the number (i.e. a one digit institution identifier would have three zeroes appearing before it). Some repetition in identifiers has been necessary in recent years, but overlap is seldom permitted within the same Federal Reserve district.

As originally assigned, the identifiers of reserve city banks were their clearing house numbers. Outside of reserve cities, institution identifiers were given in the relative order of the population of the cities in each state. Multiple banks in a city were numbered according to seniority of organization.

Certain ranges of institution identifiers are reserved for use by special classes of organizations. For instance, in Puerto Rico, only identifiers 200-299 are used; in Guam, only 500-599, etc. The identifier numbering range 7000-9999 is reserved for thrift institutions regardless of location.

C. The Check Digit

The check digit is the result of mathematical calculations that are used to verify the accuracy of the routing number. It is critical to the integrity of electronic and telecommunications transactions, and must also appear in print with the rest of the digits.

To calculate the check digit, a routine called "Modules 10, Straight Summation" is used. The formula for calculation is as follows:

Routing Symbol

ABA  Institution

by x

























(add)= 123

To 123, add the number that takes it to the next highest number ending in zero.

123 + 7 = 130, so 7 is the check digit.

Here is JavaScript code to calculate and validate the checksum.

function calc_ABA_routeno_sum(r) {
	var s=0,m=0,n=new Array(3,7,1); // here is the array of magic numbers
	for (var i=0; i<r.length; i++) {
		s += parseInt(r.charAt(i))*n[m];
//pick off the next digit, multiply it by the magic number and add it to the total
//		document.write('<BR>m='+m+' (n[m]='+n[m]+') * (r='+r.charAt(i)+') : (s='+s+')');
		m=(++m<3?m:0); //There are only three magic numbers
	return s

function check_ABA_routeno(r) {
	var s='';
	for (var i=0; i<r.length; i++) {
		if ( !isNaN( r.charAt(i) ) ) s+= r.charAt(i)
	if (s.length!=9) return false;
	var c = calc_ABA_routeno_sum(s);
	return c && c%10==0 ? true : false;
	// checksum has to be a number (not zero) and a multiple of 10.

When printed on a check or draft, the MICR number appears as a full nine-digit number with no intervening spaces, dashes or other symbols.

Fractional Form

The fractional form of the routing number is shown most commonly as a multi-digit fraction with a hyphenated numerator and a three or four-digit denominator. Each part is labeled in the number below.

City Prefix 1 2 - 3 4 5 ABA Institution Identifier

6 7 8

Federal Reserve Routing Symbol

The geographical base for the ABA's original numbering system was the network of reserve cities in existence at that time. The city prefix served to identify the source of the document by city (or by state). Numbers 1 through 49 belonged to reserve cities and major banking centers, who were assigned the numbers in order of their populations.

Numbers 50 through 99 designated the states and were assigned in east-to-west order. The numbers 50, 60, 70, 80 and 90 were given to states containing the principal collecting centers - New York, Pennsylvania, Illinois, Missouri and California, respectively. Succeeding numbers in each group were assigned to the states surrounding these collecting centers; exceptions were Hawaii and Alaska, whose prefixes were assigned long after those of the older states. Prefix number 101 was designated for use by territories and dependencies. The complete list of city and state prefix numbers appears following this explanatory section.

The fractional form of the routing number, like the MICR, also includes the Federal Reserve routing symbol and the institution identifier but with these differences:

1.  The institution identifier appears as part of the hyphenated numerator and significant zeroes are dropped (a one digit institution identifier would be printed without three zeroes preceding it).

2.  The Federal Reserve routing symbol appears as the three or four digit denominator and in districts 1 through 9, the zero is dropped from the first position of the symbol.

Other Types of Routing Numbers

0000 Series. United States Treasury Checks and Postal Money Orders: acceptable for immediate credit at any Federal Reserve office. (Note: Savings Bonds must be processed through the EZ Clear program as of February, 1991.)

4000 Series. Reserved for future use: these numbers may be used only with permission from the American Bankers Association.

5000 Series. Internal Processing Numbers: reserved for use by depository financial institutions and the Federal Reserve in connection with their internal process control procedures. Under no circumstances should "5000" series numbers be encoded on items which go into the check collection system.

6000 - 7000 Series. Electronic Transaction Identifiers: Reserved for use as electronic addresses of non-financial institutions which process payment transactions on behalf of financial institutions. (See Routing Number Policy Section III.B and IV).

8000 Series. Reserved for use by issuers of travelers checks. (See Routing Number Policy Section III).

9000 Series. Non-Par Numbers: historically used to allow the routing of checks drawn on non-par banks (90), and banks that paid at par but, as a matter of choice, did not wish to receive their items through the Federal Reserve System (91 or 92). The use of these numbers is now considered obsolete and is under review by the American Bankers Association. To distinguish checks not collectible for face value through the Federal Reserve, a change was made in the structure of the routing symbol. The first two digits of the symbol are 90, instead of the Federal Reserve district number. And in place of the usual last two digits, the old city (or state) prefix number is used. In the sample routing number used throughout this section, then, the non-par version would appear as 9012 0345 6, with the 12 being the city prefix, the institution identifier remaining the same and the check digit recalculated.

Note: Special series of routing numbers in use are listed on page xxxv.

Routing Number Administrative Board

The administration of routing number policy and all procedures developed pursuant to the policy will be the responsibility of the Routing Number Administrative Board. See the Routing Number Policy Section V.A for a complete description of the responsibilities of the Board.

Obtaining a Routing Number

A routing number will only be issued to a Federal or State chartered financial institution which is eligible to maintain an account at a Federal Reserve Bank. The authority of an institution to provide financial or payment services is governed by the charter granted by the national or state chartering agency. The assignment of a routing number does not expand or change in any way the powers of the institution as specified in that charter.

Routing numbers will not be issued to non-financial institutions or bank holding companies. In addition, routing numbers will not be issued to third-party processors, processing centers, or operations subsidiaries of bank or bank holding companies. However, these organizations may be eligible for assignment of special purpose electronic transaction identifiers. (See Routing Number Policy Section II).

A. Rules for Assignment

In general, an institution is entitled to a single routing number that identifies the place presentment for its checks and other payment transactions. More than one number may be assigned if the institution has at least one office and a presentment point in more than one Federal Reserve Territory or state within a Federal Reserve Territory. (See Routing Number Policy Section III).

B. Retirement of Numbers

Routing numbers are officially "retired", i.e., withdrawn from the institution to whom assigned, for a variety of reasons: closing of the institution, merger with another institution; relocation to a new Federal Reserve district; or simply lack of use of the number, as in the case of some thrift institutions who have never issued draft or checking accounts.

In the case of a merger or consolidation between two or more institutions, the Routing Number Policy prescribes the retirement procedures.

The official retirement of a routing number is done to protect the integrity and intent of the numbering system. However, retirement does not necessarily mean that items bearing the retired number will no longer appear in the check collection system. These items must be handled as exceptions after the permissible grace period in each Federal Reserve district; Keybook users should contact the Federal Reserve System (FRS) Routing Number Administrator in their own Federal Reserve district for clarification of local rules. (See Routing Number Policy Section V).

The complete Routing Number Policy approved in November, 1996 begins on page ix. We strongly encourage you to review the policy.

C. Registrar of Routing Numbers

Thomson Financial Publishing serves as the American Bankers Association's official Registrar in the assigning and administering of routing numbers. Newly-organized financial institutions must apply to Thomson Financial Publishing in writing for their routing numbers, and institutions undergoing mergers or other structural changes must also notify the company to obtain clarification on continuing use of affected numbers. Changes that can impact routing number eligibility include relocation of principal office, branch purchases, opening or closing of branches or presentment points, etc.

In addition to its assigning duties, Thomson Financial Publishing is responsible for publishing the American Bankers Association Key to Routing Numbers. Thomson Financial Publishing also updates and produces a magnetic tape file called the Thomson Routing and Transit Number File, which contains all financial institutions that use routing numbers in payment processing in machine-readable form.

Applications and questions may be addressed to: Thomson Financial Publishing, Routing Number Registrar, P.O. Box 916, Skokie, IL 60076-0916.




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