The Queen celebrates two birthdays each year: her actual birthday on 21 April and her official birthday on a Saturday in June. Official celebrations to mark Sovereigns' birthday have often been held on a day other than the actual birthday, particularly when the actual birthday has not been in the summer.
To mark the real birthday of the Queen, a 41-gun royal salute it is fired by the King's Troop Royal Artillery in Hyde Park at 12.00 noon and a 62-gun royal salute at 13.00 at the Tower of London.
No other particular ceremony is carried out on this day.
The official Sovereign's birthday on the other hand has been marked since 1805 by the Trooping of the Colour ceremony normally held on the second saturday in june.
This year is a "special" birthday and 90th birthday celebrations will be one of the highlights of 2016 with events taking place in April, May and June, some of which are free and some of which require tickets, but the key is to plan ahead if you want to participate.
List of Events:
May 12-15: 90 minutes extravaganza with 900 horses and more than 1500 riders and performers each evening with the Queen attending the last evening
June 10: Service of Thanksgiving at St Paul's Cathedral
June 11: Trooping the Colour
June 12: The Patron's Lunch
Happy Birthday Ma'am and thank you for your service.