Hi
In our company, we have a practice of consolidating organization wide Headcount on monthly basis so that HR dept and all other depts are on same page regarding each dept's current manpower.
We also maintain all the necessary details of all the employees so that every information is available to us in one file.
We maintain separate MIS for attrition calculation and attrition MIS.
I am attaching a sample format of our monthly / master MIS. Hope this is of some use to you.
Regards
Deepak