Variable/Field in BEx to get from user input

Is there a way in BEx where I can create a variable/field that gets its value from user input in Webi?

Here's my scenario:

User inputs date in the prompts in Webi (MM/DD/YYYY), I want Bex to have a field that gets the MM.YYYY from the user's input and increment it by 1.

I have used a solution for this but only applies for the tables in my webi report, but it's not working for the category axis in my line chart.