Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 21 Maundy Thursday
April 22 Good Friday
April 24 Easter
April 25 Easter Monday
June 02 Feast of the Ascension
June 12 Pentecost
June 13 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)
DateTimeExtensions DateTimeExtensions