Previous Friday
=B1-CHOOSE(WEEKDAY(B1,1),2,3,4,5,6,7,1)
Last Friday of Month
=DATE(YEAR(B1),MONTH(B1)+1,0)-CHOOSE(WEEKDAY(DATE(YEAR(B1),MONTH(B1)+1,0),1),2,3,4,5,6,0,1)
or Friday previous to last day of month
=DATE(YEAR(B1),MONTH(B1)+1,0)-CHOOSE(WEEKDAY(DATE(YEAR(B1),MONTH(B1)+1,0),1),2,3,4,5,6,7,1)
2005-10-27 Thu 2005-10-21 Fri 2005-10-28 Fri 2005-10-28
2005-10-28 Fri 2005-10-21 Fri 2005-10-28 Fri 2005-10-28
2005-10-29 Sat 2005-10-28 Fri 2005-10-28 Fri 2005-10-28
2005-10-30 Sun 2005-10-28 Fri 2005-10-28 Fri 2005-10-28
2005-10-31 Mon 2005-10-28 Fri 2005-10-28 Fri 2005-10-28
2005-11-01 Tue 2005-10-28 Fri 2005-11-25 Fri 2005-11-25
2005-11-02 Wed 2005-10-28 Fri 2005-11-25 Fri 2005-11-25
2005-11-03 Thu 2005-10-28 Fri 2005-11-25 Fri 2005-11-25
2005-11-04 Fri 2005-10-28 Fri 2005-11-25 Fri 2005-11-25
2005-11-05 Sat 2005-11-04 Fri 2005-11-25 Fri 2005-11-25
2005-11-06 Sun 2005-11-04 Fri 2005-11-25 Fri 2005-11-25
2005-11-07 Mon 2005-11-04 Fri 2005-11-25 Fri 2005-11-25
2005-11-08 Tue 2005-11-04 Fri 2005-11-25 Fri 2005-11-25
2005-11-09 Wed 2005-11-04 Fri 2005-11-25 Fri 2005-11-25
2005-11-10 Thu 2005-11-04 Fri 2005-11-25 Fri 2005-11-25
2005-11-11 Fri 2005-11-04 Fri 2005-11-25 Fri 2005-11-25
2005-11-12 Sat 2005-11-11 Fri 2005-11-25 Fri 2005-11-25
2005-11-13 Sun 2005-11-11 Fri 2005-11-25 Fri 2005-11-25
2004-04-30 Fri 2004-04-23 Fri 2004-04-30 Fri 2004-04-23