Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
March 20 Maundy Thursday
March 21 Good Friday
March 23 Easter
March 24 Easter Monday
May 01 Feast of the Ascension
May 11 Pentecost
May 12 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)
DateTimeExtensions DateTimeExtensions