Memorial Day:

=IF(DATE(YEAR(NOW()),5+1,0)-WEEKDAY(DATE(YEAR(NOW()),5+1,0)+5)DATE(YEAR(NOW() ),MONTH(NOW()),DAY(1)),DATE(YEAR(NOW()),5+1,0)-WEEKDAY(DATE(YEAR(NOW()),5+1,0)+5),DATE(YEAR(NOW() )+1,5+1,0)-WEEKDAY(DATE(YEAR(NOW())+1,5+1,0)+5))

Thanksgiving Day:

=IF(DATE(YEAR(NOW()),11,1)+7-WEEKDAY(DATE(YEAR(NOW()),11,1)-DAY(DATE(YEAR(NOW()),11,1))+8-5)+(4-1)*7DATE(YEAR(NOW()),MONTH(NOW()),DAY(1)),DATE(YE AR(NOW()),11,1)+7-WEEKDAY(DATE(YEAR(NOW()),11,1)-DAY(DATE(YEAR(NOW()),11,1))+8-5)+(4-1)*7,DATE(YEAR(NOW())+1,11,1)+7-WEEKDAY(DATE(YEAR(NOW())+1,11,1)-DAY(DATE(YEAR(NOW())+1,11,1))+8-5)+(4-1)*7)

Labor Day:
=IF(DATE(YEAR(NOW()),9,1)+7-WEEKDAY(DATE(YEAR(NOW()),9,1)-DAY(DATE(YEAR(NOW()),9,1))+8-2)+(1-1)*7DATE(YEAR(NOW()),MONTH(NOW()),DAY(1)),DATE(YE AR(NOW()),9,1)+7-WEEKDAY(DATE(YEAR(NOW()),9,1)-DAY(DATE(YEAR(NOW()),9,1))+8-2)+(1-1)*7,DATE(YEAR(NOW())+1,9,1)+7-WEEKDAY(DATE(YEAR(NOW())+1,9,1)-DAY(DATE(YEAR(NOW())+1,9,1))+8-2)+(1-1)*7)