Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 03 Maundy Thursday
April 04 Good Friday
April 06 Easter
April 07 Easter Monday
May 15 Feast of the Ascension
May 25 Pentecost
May 26 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)
DateTimeExtensions DateTimeExtensions