Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 11 Maundy Thursday
April 12 Good Friday
April 14 Easter
April 15 Easter Monday
May 23 Feast of the Ascension
June 02 Pentecost
June 03 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)
DateTimeExtensions DateTimeExtensions