Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
March 22 Maundy Thursday
March 23 Good Friday
March 25 Easter
March 26 Easter Monday
May 03 Feast of the Ascension
May 13 Pentecost
May 14 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)
DateTimeExtensions DateTimeExtensions