Thank you for your response. After creating those reference dates I used them as my dimension axes in the chart.
For my expression, I did what you mentioned.
By doing that, it only took 'Active' contracts and didnt take any contracts which were 'Active' before but are 'Expired' now. I would like to show those contracts too which were 'Active' before and are 'Expired' now with in their time range.
I guess, if I dont provide this condition in the expression; than I get what I want?