Key Difference: The American Bankers Association (ABA) number is an identification number that appears in the upper right corner of the check in the form of a fraction. The number is used to identify the location of the bank and the code bank and the area and bank on which it is drawn. Another code that is present on the check is the ABA Routing Number, also known as the Routing Transit Number (RTN). This is a nine-digit code that is located on the bottom left hand corner of the check and will be preceded by the ‘|:’ transit character.

In order to make it easier to keep track of checks and the flow of money, the American Bankers Association (ABA) came up with a few codes that could easily keep track of the flow of money and the checks that were being circulated in the economy. In absence of this numbering system by the ABA, there would be a mass confusion as to where the money was coming from and going to. These codes also help prevent check frauds. Incomplete numbers or a fault in these numbers cost financial institutions and people a lot of money in loss of transactions or missing transactions. These numbers should always be accurately provided.

The American Bankers Association (ABA) number is an identification number that appears in the upper right corner of the check in the form of a fraction. The number is used to identify the location of the bank and the code bank and the area and bank on which it is drawn. The top half of the fraction identifies the district of the bank, while the bottom half identifies the Federal Bank that services the financial institution that issued the check. The association is responsible for assigning a unique code for each bank and location. The ABA numbers are more commonly becoming obsolete and are being replaced by the Routing Transit Number.

Let’s take an example 11-44545/5794. The first part of the numerator ‘11’ identifies the district that the bank is located in. The second-half ‘44545’ is the unique code that has been assigned to the bank. The denominator ‘5794’ refers to the Federal Bank that is in collaboration with this financial institution and serves it.

Another code that is present on the check is the ABA Routing Number, also known as the Routing Transit Number (RTN). This is a nine-digit code that is located on the bottom left hand corner of the check and will be preceded and followed by the ‘|:’ transit character. Similar to the ABA Number this code identifies the unique number of the financial institution from which the check is drawn and the code of the Federal Reserve Bank that serves this particular financial institution.

The first two digits of the routing number must be in the ranges 00 through 12, 21 through 32, 61 through 72, or 80. The first two digits correspond to the 12 Federal Reserve Banks located in various different states. The third digit corresponds to the Federal Reserve check processing center originally assigned to the bank, while the fourth digit is "0" if the bank is located in the Federal Reserve city proper, and otherwise is 1–9, according to which state in the Federal Reserve district it is. Routing numbers are also more commonly being used for electronic transfers, bill payments, online banking and automated transfers.

Using the same example above, 11-44545/5794; the nine-digit routing number will be 579444545.

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