Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 01 Maundy Thursday
April 02 Good Friday
April 04 Easter
April 05 Easter Monday
May 13 Feast of the Ascension
May 23 Pentecost
May 24 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)
DateTimeExtensions DateTimeExtensions