Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 12 Maundy Thursday
April 13 Good Friday
April 15 Easter
April 16 Easter Monday
May 24 Feast of the Ascension
June 03 Pentecost
June 04 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)
DateTimeExtensions DateTimeExtensions