I'm almost embarrassed to post this because its sheer length leads me to believe something more efficient is possible. In case it helps you, however, I'll post it anyway.
I'm assuming your list begins in A1
with the manually-entered date.
In A2
, I have the following formula:
=IF(MONTH(A1+14)=MONTH(A1),A1+14,EOMONTH(A1,0)-IF(WEEKDAY(EOMONTH(A1,0),16)<=2,WEEKDAY(EOMONTH(A1,0),16),0))
Then in A3
, I have the following formula (which you can drag down as far as you need):
=IF(A2=EOMONTH(A2,0)-IF(WEEKDAY(EOMONTH(A2,0),16)<=2,WEEKDAY(EOMONTH(A2,0),16),0),A1+14,IF(MONTH(A2+14)=MONTH(A2),A2+14,EOMONTH(A2,0)-IF(WEEKDAY(EOMONTH(A2,0),16)<=2,WEEKDAY(EOMONTH(A2,0),16),0)))
Good luck!
EDIT: I'm also assuming that non-working days are defined as Saturdays and Sundays (with no regard for holidays). Holidays will add some more complexity.