Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
March 30 Maundy Thursday
March 31 Good Friday
April 02 Easter
April 03 Easter Monday
May 11 Feast of the Ascension
May 21 Pentecost
May 22 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)
DateTimeExtensions DateTimeExtensions