How to calculate which employees worked at least one day in a month

I am trying to figure out how to calculate if an employee worked at least one day in a month based on their hire date and termination date (if they have one). I've been using conditional formatting in the past to identify who did not work in the month, but it takes more time to do the calculation using that method. Is there a way to figure out from a list of employees how many of them worked during a specific month/year and have the result total up those employees?