The tradition of Queen's Day as a holiday began before the World War II. Initially it celebrated the birthday of Queen Wilhelmina on 31 August.
Since 1949, the day has celebrated of the birthday of Wilhelmina's daughter, Queen Juliana, on 30 April.
The tradition of changing the holiday to match the birthday of the reigning queen stopped when Queen Beatrix succeeded Juliana in 1980.
Beatrix decided to keep that the Queen's Day on April 30 as a tribute to her mother. Additionally her own birthday is at the end of January 31, so celebrating it outdoors would be difficult.
In January 2013, Queen Beatrix announced that on Queen’s Day in 2013, she would abdicate in favour of her son, Crown Prince Willem-Alexander. Therefore 30 April 2013 will be the last Queen's Birthday day until the next female monarch. As it stands, 30 April will no longer be an official public holiday. Willem-Alexander was born on 27 April, which falls on a Saturday in 2014.
In January 2014, it was announced that King's Day will be celebrated on 27 April, unless it falls on a Sunday, in which case, Saturday 26 April will be observed as a holiday.