Anurag - let us know if you still require assistance on this - there is a very good article here http://community.qlik.com/blogs/qlikviewdesignblog/2012/10/12/accumulative-sums that explains this using QlikView - but you can use these in Sense using expressions with the Load Editor - or within the Master Items to create new measures with these calculations.
If you attach your sample data, we can get a better idea of the structure.
Using rangesum is the correct way to go as krisbalow mentioned.
I created some sample data (on what I best thought met your need and got this calculation:
sum( aggr( rangesum( above( (sum(Exit)/sum(active)),0,12) ),Month))
I am using SUM because my Exit and Active values are either 1 or 0.
Let us know.
In Qlikview I Want to create view like http://community.qlik.com/message/163026#163026
I am attaching EMP.XLS which as DOJ (Date of join) and DOL (date of leaving) and s_active
Can you give guide me how to achieve the same in Qlikview.