Wednesday 01 Jan New Year's Day
Wednesday 16 Apr Half trading day (Wednesday before Easter)
Thursday 17 Apr Maundy Thursday
Friday 18 Apr Good Friday
Monday 21 Apr Easter Monday
Thursday 01 May Labour Day
Thursday 29 May Ascension Day
Monday 09 Jun Whit Monday
Wednesday 24 Dec Christmas Eve
Thursday 25 Dec Christmas Day
Friday 26 Dec Boxing Day
Wednesday 31 Dec New Year's Eve
Source: http://www.nasdaqomxnordic.com/tradinghours/