Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 23 Good Friday
April 25 Easter
April 26 Easter Monday
June 03 Feast of the Ascension
June 13 Pentecost
June 14 Pentecost Monday
August 31 Kingsday
December 25 Christmas
December 26 Boxing Day
DateTimeExtensions DateTimeExtensions