Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 01 Good Friday
April 03 Easter
April 04 Easter Monday
May 12 Feast of the Ascension
May 22 Pentecost
May 23 Pentecost Monday
August 31 Kingsday
December 25 Christmas
December 26 Boxing Day
DateTimeExtensions DateTimeExtensions