How can i get count the days employee must work in any month ?

Hi all,
i hope that to find help and found how to do that 
i have creat table in my database and i add days as bit and save the days that employee must work in week and i can get the count of work days at week for each employee

i need that to get how many days must employee work in any month becouse i have many employee each one of them his work days in week not the same for all 
some employee work (3 days in week) , other work (4 days in week), other work (6 days work) so i need to get how many days employss must ...