In the MICR line, the draft number is generally in positions 17-14, but can occupy positions 17-13.  The ANSI standards do not dictate that position 13 must remain vacant. 

If your credit union uses a 14-digit MICR, there is usually only room for up to a four-digit check number on the bottom of the checks. There is a risk of overwriting the check number if you use a five-digit check number. 
  • If you use anything less than a 14-digit MICR, there is no problem with a five-digit check number.