Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 07 Maundy Thursday
April 08 Good Friday
April 10 Easter
April 11 Easter Monday
May 19 Feast of the Ascension
May 29 Pentecost
May 30 Pentecost Monday
December 25 Christmas
December 26 Christmas (2nd Day)
DateTimeExtensions DateTimeExtensions