Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 06 Maundy Thursday
April 07 Good Friday
April 09 Easter
April 10 Easter Monday
May 18 Feast of the Ascension
May 28 Pentecost
May 29 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)
DateTimeExtensions DateTimeExtensions