Add Bussiness Days Methods

I need to draw a line from DateStart to DateStart.AddDays(5)( I mean I didnt know EndDate but can calculate it Incrementally like Start+5). Everything works well until there is a weekend between these points, then the line turns out to be cut.

There are many suggestions on how to calculate for weekends here https://stackoverflow.com/questions/1044688/addbusinessdays-and-getbusinessdays. But I would like to have built-in functionality.