Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 05 Maundy Thursday
April 06 Good Friday
April 08 Easter
April 09 Easter Monday
May 17 Feast of the Ascension
May 27 Pentecost
May 28 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)
DateTimeExtensions DateTimeExtensions