Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 11 Good Friday
April 13 Easter
April 14 Easter Monday
May 22 Feast of the Ascension
June 01 Pentecost
June 02 Pentecost Monday
August 31 Kingsday
December 25 Christmas
December 26 Boxing Day
DateTimeExtensions DateTimeExtensions