When you set a parameter based on a date field and allow any value, you can allow users to choose relative dates in both viewing and scheduling reports. This allows you to set up scheduling that always updates automatically, with no need to go in and set the dates each time.
When you show the report in the viewer and it requests parameter values, you can drop down the date parameter and select either Specific Date or Relative Date. Specific Date shows you the calendar picker that you would normally see for a date, but Relative Date offers the following options.
These dates are relative to the date that the report runs, and the week range values are determined based on the report's culture rather than the server's culture.
Images of Specific Date and Relative Date options
When you schedule the report and specify report parameters, you are given the same choice of Specific or Relative Date.