File ID Modifier

 

The File ID Modifier is located in the File Header Record, position 34, and can be numeric (0-9) or alphabetic (A-Z).
 

It is used by the financial institution to differentiate between multiple files transmitted on the same day.

 

For example, the first file transmitted on particular day will have the value of '1'.  The second will be '2', the third '3' and so on.

On the next day, the file modifier is automatically reset back to '1' for the first file.

 

While some banks show an example of A, B, C - in their documentation, you can use 1, 2, 3 just the same.