There should still be no need for loops. Amit Lohia's response was closest to what I figured a non-loop solution would be. If the "flaw" he refers to are holidays that fall on weekends, the solution is simple. Have your table contain the holiday's date and weekday, SELECT and COUNT() those entries that don't fall on weekends, then you may count the number of weekends within your time period and voilà, you have your count.

So deadlineDate = dtStart + iBizDays + modified table count + count of weekend days

The only thing you have to be careful about are off-by-one issues that may arise with dtEnd and/or dtStart falling on weekends and/or holidays, but those are logic issues that don't need loops for a resolution.

If there is yet another flaw in that logic, please let me know. I'm sure it can still be resolved functionally instead of procedurally.