Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
March 29 Maundy Thursday
March 30 Good Friday
April 01 Easter
April 02 Easter Monday
May 10 Feast of the Ascension
May 20 Pentecost
May 21 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)
DateTimeExtensions DateTimeExtensions