Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 15 Good Friday
April 17 Easter
April 18 Easter Monday
May 26 Feast of the Ascension
June 05 Pentecost
June 06 Pentecost Monday
August 31 Kingsday
December 25 Christmas
December 26 Boxing Day
DateTimeExtensions DateTimeExtensions