This QlikView shows how buttons can be used to increment or decrement date variables.
Where expressions call for comparisons to dates these can often be looked up from a date table. Better performance and improved manageability can be obtained by comparing to dates stored in a variable. Variables can be updated from data in the model or via triggers, but I find a better approach is to use buttons and actions.
The QlikView was originally written as a response to the following QlikCommunity thread
Further examples of using Actions can be found in this blog post and Video: http://bit.ly/15PEpQ9