Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
March 25 Good Friday
March 27 Easter
March 28 Easter Monday
May 05 Feast of the Ascension
May 15 Pentecost
May 16 Pentecost Monday
August 31 Kingsday
December 25 Christmas
December 26 Boxing Day
DateTimeExtensions DateTimeExtensions