Hello,
I am new to using MS Projects and I am trying to create a 3 Week Look ahead. I have done some research and it seems the best option is to create a Custom Field and then a Custom View Flag. I have used the below formula but when I go to use the filter all my activities go away. Any help would be greatly appreciated. I am using 2013 Projects.

([Start]<([Current Date]+21) Or [Finish]<([Current Date]+21)) And [% Work Complete]<100

Thanks