Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
March 31 Easter
April 01 Easter Monday
May 01 LabourDay
May 09 Feast of the Ascension
May 19 Pentecost
May 20 Pentecost Monday
July 21 Belgium_NationalHoliday
August 15 Assumption
November 01 All Saints
November 11 Armistice
December 25 Christmas
DateTimeExtensions DateTimeExtensions