Why not break it down into simple steps so that it is easier to understand, and then when you do understand condense it into a single expression.
1) Set a variable as a date
2) Subtract your choice of value from said variable
3) Convert said variable into a date format
So basically, exactly as Enrico has said above
![Mr. Green :mrgreen:](https://www.ibmmainframeforum.com/images/smilies/icon_mrgreen.gif)