Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 13 Maundy Thursday
April 14 Good Friday
April 16 Easter
April 17 Easter Monday
May 25 Feast of the Ascension
June 04 Pentecost
June 05 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)
DateTimeExtensions DateTimeExtensions