Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
March 22 Good Friday
March 24 Easter
March 25 Easter Monday
May 02 Feast of the Ascension
May 12 Pentecost
May 13 Pentecost Monday
August 31 Kingsday
December 25 Christmas
December 26 Boxing Day
DateTimeExtensions DateTimeExtensions