get last 24 months data from user response webi 4.1

Hi Guys

I need to display last 2 years of data based on the what date the user enters:

If the user enters 01/01/2015, I need to see data from 01/01/2013 to 01/01/2015

The date will be entered in dd/mm/yyyy (datetime) format.

How do I achieve this in Webi?

cheers