How to set cell 00/1-20/000 to move to another cell
 

How do I set one cell (logical if question) to enter a date range example
(00/1-20/0000 to automatically show payperiod date. This is a simple
commission with completion dates so that excell will automatically calculate
the correct totals based on competion dates to pay-period??? Example (if you
get paid commission on completed sales from the 21st of any month through the
20th of the following month) How would I show a date range logical if
question to move this automatically into the correct pay-period????